CPCWiki forum

Hello!

I'm new to this forum, based in Norway, and have recently pulled my old Amstrad CPC 6128 out of storage (very poor storage).

I am having the grey screen, black frame issue, and have been reading up on it on this forum, and watching some videos by Noel's retro on Youtube. BTW, no beep when holding "DEL" button.

I have checked the following:

I tried the trick with removing PAL/FAL chip and forcing second RAM bank, as described in this forum, with no change.
Is it possible that I'm having issues with both banks?

I've tested the clocks with a multimeter, finding the clocks to the CRTC to be 1Mhz, the Z80 to be 4Mhz and the Gate Array (40010) to be 16Mhz as described in another thread in the forum. All seem to be correct.

I checked voltages on all chips, and they are currently at 4,6V, maybe a little low? I am using the original monitor as power supply, and tested the plug and found approx 5,1V.
However, while testing the voltages on IC114, IC115 and IC116 (gate array) I found the voltage to be only approx 2,6V. I'm not sure if i tested the correct pins on these though.

I also used a thermal camera on the board. With the camera, I could see that the temperatures were quite even on almost all chips, approx 30 degrees C. However, the Z80 showed a temperature of up to 60 degrees C (maybe over, depending on my camera), the PAL/FAL and the CRTC showed approx 40 degrees C.

I've ordered a new Z80 as these were quite cheap on Ebay, and found it "nice to have". Considering buying 16 new RAM chips with slots.

Today I fiddled a bit with the power supply plug from the monitor (5V), due to bad contact, maybe due to a bit corrosion in the plug, and sometimes the the grey field in the screen turned to small blue and yellow squares. This made me a bit suspicious towards the power supply also. Maybe I should buy an external one?

As far as I know, the computer has never been subject to over voltage. It as only been used with power supply from the monitor. However, it has been stored in a pretty rough enviroment, but there arent any visual corrosion.

I am hoping for tips on things I can check while waiting for my new Z80?

I've also seen that some of you have this "component" you plug in on the back of the computer (M4??) with a program to test the RAM banks. Is this unit with the program for sale somewhere? In that case I would appreciate a link.

I apologize for a messy post, and maybe some bad english.

I have some education and experience in soldering and house/ship electrics, but my experience in electronics is somewhat limited. However, I'm a fast learner.

I would really like to get this repaired, as it was a christmas present from my parents in 1988/89, and now I want to show it to my step-children.

Any tips would be appreciated, thank you!

Try to bypass the CPC6128 Power Switch (just jumper it on the PCB) - I suspect the reason for your low voltages...

Quote from: RetroCPC on 13:18, 13 February 23Try to bypass the CPC6128 Power Switch (just jumper it on the PCB) - I suspect the reason for your low voltages...

Thank you for your answer, I tried that now, but sadly the same result. After removing the connector for the on/off swictch, I also measured the connector on the circuit board, and it read 5,1V, so the voltage issue seems to be "later" in the circuit.

blue pixels on gray screen suggests one or more 74LS153 MUX chips is bad...

the "component" youre looking for is Bryces Lower ROM board..with diagnostics loaded into the rom...
it wont help with gray screen!.. it may show the memory as all bad even tho its fine and its the MUX chips causing the problem.. 

Quote from: WacKEDmaN on 15:52, 13 February 23blue pixels on gray screen suggests one or more 74LS153 MUX chips is bad...

the "component" youre looking for is Bryces Lower ROM board..with diagnostics loaded into the rom...
it wont help with gray screen!.. it may show the memory as all bad even tho its fine and its the MUX chips causing the problem..

Thanks, I located those chips. Are there any way to test these chips, by voltage, frequency (hz) or temperature?

The blue and yellow squares appeared only once by fiddling with the power supply plug, so the issue seems to be the grey screen with black border.

even without the blue pixels.. just the gray screen... id still say one of the MUX chips...
theres no way to test them on board (unless you have an oscilloscope to actually check each line to make sure they are all outputing and the signal levels are correct)...

i forgot to mention, you can burn the diagnostics rom to a new eeprom, and replace the CPCs original ROM with it to test, instead of using the lower rom board..

Quote from: WacKEDmaN on 16:08, 13 February 23even without the blue pixels.. just the gray screen... id still say one of the MUX chips...
theres no way to test them on board (unless you have an oscilloscope to actually check each line to make sure they are all outputing and the signal levels are correct)...

i forgot to mention, you can burn the diagnostics rom to a new eeprom, and replace the CPCs original ROM with it to test, instead of using the lower rom board..

Ok, thanks, I will have to look into that then!

Quote from: oyshals on 13:27, 13 February 23

Quote from: RetroCPC on 13:18, 13 February 23Try to bypass the CPC6128 Power Switch (just jumper it on the PCB) - I suspect the reason for your low voltages...

Thank you for your answer, I tried that now, but sadly the same result. After removing the connector for the on/off swictch, I also measured the connector on the circuit board, and it read 5,1V, so the voltage issue seems to be "later" in the circuit.

Have you found the drop in voltage? When I use a new CPC for the first time, I use a current limiting bench power supply just incase there are any shorts. I find the service manual and the circuit diagram very useful.

Not yet, off to work now, will continue tomorrow. Is 4,6v to low for the computer to run? I'm also curious about the IC114, 115 and 116 which I measured to 2,6v, there might be something there. I just hope it isn't IC116, the gateway arrey, i understand that one is irreplacable!

I have a lot of reading to do in the manual, but correct voltages has been difficult to find...

Quote from: oyshals on 17:58, 13 February 23Not yet, off to work now, will continue tomorrow. Is 4,6v to low for the computer to run? I'm also curious about the IC114, 115 and 116 which I measured to 2,6v, there might be something there. I just hope it isn't IC116, the gateway arrey, i understand that one is irreplacable!

I have a lot of reading to do in the manual, but correct voltages has been difficult to find...

I guess 4.6V is ok and the fact that you have measured a clock from the GateArray indicates it at least is running. I Think VDD pins are 6 and 25 on the GA. ICs 114 and 115 are standard 74 series so should be pin 20 for Vcc and 2.6v sounds too low but check your connection onto the pin just incase.

Quote from: Rabs on 18:17, 13 February 23

Quote from: oyshals on 17:58, 13 February 23Not yet, off to work now, will continue tomorrow. Is 4,6v to low for the computer to run? I'm also curious about the IC114, 115 and 116 which I measured to 2,6v, there might be something there. I just hope it isn't IC116, the gateway arrey, i understand that one is irreplacable!

I have a lot of reading to do in the manual, but correct voltages has been difficult to find...

I guess 4.6V is ok and the fact that you have measured a clock from the GateArray indicates it at least is running. I Think VDD pins are 6 and 25 on the GA. ICs 114 and 115 are standard 74 series so should be pin 20 for Vcc and 2.6v sounds too low but check your connection onto the pin just incase.

Thanks, I'll focus on that area tomorrow while waiting for parts. I will also be ordering som MUX chips as @WacKEDmaN suggested, as they were very cheap. Thanks for the help so far everyone!

I found something. One of the capacitators for one of the ram chips looks damaged. Som of the insulation on top of it looks like it has snapped off. Could it be blown, and could it be that simple?  :doh:

Quote from: oyshals on 21:28, 13 February 23I found something. One of the capacitators for one of the ram chips looks damaged. Som of the insulation on top of it looks like it has snapped off. Could it be blown, and could it be that simple?  :doh:

possibly...if its shorted... remove it and see if ya voltage drop changes... ya should be able to test it fine without the capacitor.. its just for smoothing power...

Quote from: WacKEDmaN on 21:47, 13 February 23

Quote from: oyshals on 21:28, 13 February 23I found something. One of the capacitators for one of the ram chips looks damaged. Som of the insulation on top of it looks like it has snapped off. Could it be blown, and could it be that simple?  :doh:

possibly...if its shorted... remove it and see if ya voltage drop changes... ya should be able to test it fine without the capacitor.. its just for smoothing power...

Thanks! I'll give it a try tomorrow!

This might be a stupid question, it's been over 20 years since i had electronics at school; is it possible to measure of there is a shortage in a capacitator with a multimeter? It would be nice if I could check all of them if there's an issue with the one...

you can check for shorts with multimeter.. continuity mode.. and probe both legs.. 
you cant test capacitors in circuit (to check its capacitance is correct)..you need to remove it and then test it ...if your multimeter can measure capacitance!
if you try to check capacitance with caps on the board, you are actually measuring the total capacitance of the board...eg all the caps and any other parasitic capacitance

No luck, no shorts on the capacitators. I watched a troubleshooting video by Noel's Retro last night, he had 4,8 volts and said that was a bit low. I only have 4,6 volts, so I'll keep looking.

Quote from: oyshals on 12:43, 14 February 23No luck, no shorts on the capacitators. I watched a troubleshooting video by Noel's Retro last night, he had 4,8 volts and said that was a bit low. I only have 4,6 volts, so I'll keep looking.

It is a little low but you indicated you have a clock out of the GA. The 2.6V is more of a concern. Are you still sering this? I recently had a grey screen (total RAM failure). Turned out to be a dry joint on the power header connector on the PCB.

As a rule with any new CPC  I always check for a stable voltage across the PCB. Also I clean the power switch and reflow power connectors to eliminate any dry joints both external and the internal PCB header connector.

Quote from: Rabs on 13:36, 14 February 23As a rule with any new CPC  I always check for a stable voltage across the PCB. Also I clean the power switch and reflow power connectors to eliminate any dry joints both external and the internal PCB header connector.

The 2,6v is no longer a concern, turns out i measured the wrong pins. So the voltage is now the same all over, 4,6-4,7 volts. I will find my soldering gear to try reflowing, I didn't think of that. I started to suspect that the old power supply in the monitor was starting to fail, and couldn't handle the load anymore (sometimes happens on larger electrical plants).

My Z80 is a bit hot though, approx 60 degrees C, but I'm thinking thats not abnormal for a CPU?

Still seeing clock signal from GA.

60°C is too high for a Z80.

Bryce.

Quote from: Bryce on 14:46, 14 February 2360°C is too high for a Z80.

Bryce.

Thanks! I have a new one in order, also waiting for my paycheck to order new RAM, MUX, CRTC and GA, just in case. Better safe than sorry. Hopefully it's the Z80...

Quote from: oyshals on 14:31, 14 February 23My Z80 is a bit hot though, approx 60 degrees C, but I'm thinking thats not abnormal for a CPU?

Check if the Z80 is alive. I would check for clock input, pin 6, and then for activity on M1, pin 27.

Quote from: Rabs on 19:00, 14 February 23

Quote from: oyshals on 14:31, 14 February 23My Z80 is a bit hot though, approx 60 degrees C, but I'm thinking thats not abnormal for a CPU?

Check if the Z80 is alive. I would check for clock input, pin 6, and then for activity on M1, pin 27.

Thanks! I'll look into that, last I checked, I found the clock to be correct, the M1 I will check tomorrow.

Another stupid question: Can I do the "piggyback" thing on all kinds of chips, or is this only for the RAM?

Quote from: oyshals on 19:19, 14 February 23Another stupid question: Can I do the "piggyback" thing on all kinds of chips, or is this only for the RAM?

Sorry, not something I have experience of. I would always check the signal data when attempting to make a diagnosis as to whether an IC is faulty.

Quote from: oyshals on 19:19, 14 February 23Another stupid question: Can I do the "piggyback" thing on all kinds of chips, or is this only for the RAM?

As far as I understood, it depends on the type of defect. If the defect results in a short, piggyback will probably not work. 

Thanks for all answers so far!

I thought I had found RAM chips with sockets on eBay, but looking more closely, it was for the 6128 plus.

Noe I've googles "MN4164P-15", and found several different ones with this spec. But does the writing on the bottom matter? I have two different kinds: "Japan 52535" and three that says "4D3-15"

I've decided to order all the chips I can, either for use or for spare, as I'm not giving this CPC up!

MN4164P is just a 4164 manufactured by Panasonic. There were many manufacturers, so you want to search for "4164 DRAM" not just a specific part number. All the other markings are dates/batch codes/manufacturer internal markings that you don't need to worry about.

Quote from: oyshals on 09:56, 15 February 23Thanks for all answers so far!

I thought I had found RAM chips with sockets on eBay, but looking more closely, it was for the 6128 plus.

Noe I've googles "MN4164P-15", and found several different ones with this spec. But does the writing on the bottom matter? I have two different kinds: "Japan 52535" and three that says "4D3-15"

I've decided to order all the chips I can, either for use or for spare, as I'm not giving this CPC up!

Keep going, they are all fixable. Easier to check RAM failures with the Diagnostic ROM, but you could check for activity on the RAM data out pin. Was there activity on the Z80 M1 pin?

Quote from: Rabs on 10:29, 15 February 23

Quote from: oyshals on 09:56, 15 February 23Thanks for all answers so far!

I thought I had found RAM chips with sockets on eBay, but looking more closely, it was for the 6128 plus.

Noe I've googles "MN4164P-15", and found several different ones with this spec. But does the writing on the bottom matter? I have two different kinds: "Japan 52535" and three that says "4D3-15"

I've decided to order all the chips I can, either for use or for spare, as I'm not giving this CPC up!

Keep going, they are all fixable. Easier to check RAM failures with the Diagnostic ROM, but you could check for activity on the RAM data out pin. Was there activity on the Z80 M1 pin?

It's hard to say, I havent aquired an oscilloscope yet, but I'm getting som activity using the multimeter on Hz, approx 0,8MhZ (not constant). Voltage on this Pin i 2,2V. Edit: This is on the M1 port.

I am not familiar with the diagnostics rom, would an external on work? like this one: https://www.ebay.com/itm/265807524689?hash=item3de35cf351:g:768AAOSwKz5i55lw&amdata=enc%3AAQAHAAAAsN9%2Bcp7MiyicgOLUBvKfgCncDqycx4h1JQkXrlZ%2Bg8hht4gwR5J7oDHi2tfOHoXRBKbv%2Bpp392LLulmuKKqW5l7troLAARmPpKVKMl8Aib6eQ7z4IVv%2FjrP6sfWFu1yckU6ZmlbxBMmT8sMHQkixqTQlzqeUi7imkl4hZLX7g7HhSgpMTgQINv4y1Bxacyt04C6oRa6dRqh%2B1SSDtySSEILRiQnN9o6rbtVHJHezTr%2Fr%7Ctkp%3ABk9SR47UwsnKYQ

I have not used the Dandinator so can't really advise but believe so. I use a ROM board which allows it to act as the lower ROM.

I'm sorry that I'm a bit messy, just trying to check everything.

When studying the back side of the mother board, i noticed that the color of the solderings for IC112 is a bit yellow-ish. It looks more like heat than corrosion. From the schematics, the IC112 seems to be connected to the 16MhZ clock signal, and this signal is good. Is this something to look into?

Quote from: oyshals on 12:12, 15 February 23I'm sorry that I'm a bit messy, just trying to check everything.

When studying the back side of the mother board, i noticed that the color of the solderings for IC112 is a bit yellow-ish. It looks more like heat than corrosion. From the schematics, the IC112 seems to be connected to the 16MhZ clock signal, and this signal is good. Is this something to look into?

Is it flux residue?

I think I'll give you all a break until I get the new Z80 and gate array now :)

Right now I'm leaning a bit towards the Z80 as it is very hot, and the voltage seems to drop a bit with that installed 0,1-0,2V, and I haven't found anything else out of order with my limited tools and experience.

Thanks for all the help so far, I've already learnt alot  :)

Quote from: Rabs on 12:07, 15 February 23I have not used the Dandinator so can't really advise but believe so. I use a ROM board which allows it to act as the lower ROM.

Is there a way for me to get my hands on the rom board with a working diagnostic rom? I've searched on eBay, but the only tool I can find is the Dandinator.

Think the Dandinator is your best option, just I have never used one. I am sure someone else can advise. Don't know if all ROM boards allow a ROM to act as the lower ROM and then you will need to program the ROMS, so a bit more involved.

Quote from: oyshals on 19:19, 14 February 23

Quote from: Rabs on 19:00, 14 February 23

Quote from: oyshals on 14:31, 14 February 23My Z80 is a bit hot though, approx 60 degrees C, but I'm thinking thats not abnormal for a CPU?

Check if the Z80 is alive. I would check for clock input, pin 6, and then for activity on M1, pin 27.

Thanks! I'll look into that, last I checked, I found the clock to be correct, the M1 I will check tomorrow.

Another stupid question: Can I do the "piggyback" thing on all kinds of chips, or is this only for the RAM?

Even for RAM I would not recommend piggyback. I doesn't really tell you anything, because it's not always guaranteed to work and it definitely
won't work on a CPU.

Bryce.

So I got my new Z80 today, and that didn't help. So now I'll just wait for my new Gate Array to arrive from Spain. Then I will order 16 new RAM chips. I will probably spend more money on repairing my 6128 than I would buying one from eBay, but where's the fun in that? Half of this process for me is about the learning 😊

When I finally get it fixed, I will probably have enough spare parts to buy another one and fix it too. 😊

I'm thinking of finally buying an oscilloscope, and learn how to use it (again).
Is it necessary to go for an expensive "industrial" one, or would a cheap one for "hobbies" be sufficient? Anything i should be looking for?

Not giving up!

One question. Is there a specific name for the sockets which fits the RAM chips? I want to be sure i order the correct sockets so they fit.

Quote from: oyshals on 14:24, 17 February 23One question. Is there a specific name for the sockets which fits the RAM chips? I want to be sure i order the correct sockets so they fit.

Standard DIP 16 Sockets should do. I get mine from DigiKey.

DILB16P-223TLF (https://www.digikey.co.uk/en/products/detail/amphenol-cs-fci/DILB16P-223TLF/4292068?s=N4IgTCBcDaIGwAYCcBaALAdgIwGYUDkAREAXQF8g)

20230218_150939.jpg

Below you can see I replaced two failed ICs in the upper RAM bank.

20221027_140035.jpg

I identified the failed ICs using the Diagnostics ROM and I would always try and identify failed ICs before removing as there is always a risk of damaging the PCB.

Quote from: oyshals on 12:59, 17 February 23So I got my new Z80 today, and that didn't help. So now I'll just wait for my new Gate Array to arrive from Spain. Then I will order 16 new RAM chips. I will probably spend more money on repairing my 6128 than I would buying one from eBay, but where's the fun in that? Half of this process for me is about the learning 😊

When I finally get it fixed, I will probably have enough spare parts to buy another one and fix it too. 😊

I'm thinking of finally buying an oscilloscope, and learn how to use it (again).
Is it necessary to go for an expensive "industrial" one, or would a cheap one for "hobbies" be sufficient? Anything i should be looking for?

Not giving up!

As you are seeing a clock from the GA, I would suspect it is ok and all indications are you have a RAM failure. The Diagnostics ROM would help you identify this.

I use a Hantek DSO5102P Digital Storage Oscilloscope and I love it.

Below you can see a trace from the Z80 Clock PIN 6.

Z80 pin 6 Clock.jpg

Quote from: pelrun on 10:09, 15 February 23MN4164P is just a 4164 manufactured by Panasonic. There were many manufacturers, so you want to search for "4164 DRAM" not just a specific part number. All the other markings are dates/batch codes/manufacturer internal markings that you don't need to worry about.

Do the access times matter or are they all going to be fast enough? My 6128s have -12 (120ms) and I replaced with -10 (100ms).

Quote from: Rabs on 16:37, 18 February 23

Quote from: oyshals on 12:59, 17 February 23So I got my new Z80 today, and that didn't help. So now I'll just wait for my new Gate Array to arrive from Spain. Then I will order 16 new RAM chips. I will probably spend more money on repairing my 6128 than I would buying one from eBay, but where's the fun in that? Half of this process for me is about the learning 😊

When I finally get it fixed, I will probably have enough spare parts to buy another one and fix it too. 😊

I'm thinking of finally buying an oscilloscope, and learn how to use it (again).
Is it necessary to go for an expensive "industrial" one, or would a cheap one for "hobbies" be sufficient? Anything i should be looking for?

Not giving up!

As you are seeing a clock from the GA, I would suspect it is ok and all indications are you have a RAM failure. The Diagnostics ROM would help you identify this.

I use a Hantek DSO5102P Digital Storage Oscilloscope and I love it.

Below you can see a trace from the Z80 Clock PIN 6.

Z80 pin 6 Clock.jpg

Thanks! Found some now 👍

After some reading on the forum i checked out the icompplus.com site and ordered some chips. Also ordered the dandanator.

Quote from: oyshals on 17:59, 18 February 23

Quote from: Rabs on 16:37, 18 February 23

Quote from: oyshals on 12:59, 17 February 23So I got my new Z80 today, and that didn't help. So now I'll just wait for my new Gate Array to arrive from Spain. Then I will order 16 new RAM chips. I will probably spend more money on repairing my 6128 than I would buying one from eBay, but where's the fun in that? Half of this process for me is about the learning 😊

When I finally get it fixed, I will probably have enough spare parts to buy another one and fix it too. 😊

I'm thinking of finally buying an oscilloscope, and learn how to use it (again).
Is it necessary to go for an expensive "industrial" one, or would a cheap one for "hobbies" be sufficient? Anything i should be looking for?

Not giving up!

As you are seeing a clock from the GA, I would suspect it is ok and all indications are you have a RAM failure. The Diagnostics ROM would help you identify this.

I use a Hantek DSO5102P Digital Storage Oscilloscope and I love it.

Below you can see a trace from the Z80 Clock PIN 6.

Z80 pin 6 Clock.jpg

Thanks! Found some now 👍

After some reading on the forum i checked out the icompplus.com site and ordered some chips. Also ordered the dandanator.

Don't forget to clean the expansion port before using the Dandanator. I use an old ink eraser and then some  isopropanol cleaning fluid.

Quote from: Rabs on 18:33, 20 February 23

Quote from: oyshals on 17:59, 18 February 23

Quote from: Rabs on 16:37, 18 February 23

Quote from: oyshals on 12:59, 17 February 23So I got my new Z80 today, and that didn't help. So now I'll just wait for my new Gate Array to arrive from Spain. Then I will order 16 new RAM chips. I will probably spend more money on repairing my 6128 than I would buying one from eBay, but where's the fun in that? Half of this process for me is about the learning 😊

When I finally get it fixed, I will probably have enough spare parts to buy another one and fix it too. 😊

I'm thinking of finally buying an oscilloscope, and learn how to use it (again).
Is it necessary to go for an expensive "industrial" one, or would a cheap one for "hobbies" be sufficient? Anything i should be looking for?

Not giving up!

As you are seeing a clock from the GA, I would suspect it is ok and all indications are you have a RAM failure. The Diagnostics ROM would help you identify this.

I use a Hantek DSO5102P Digital Storage Oscilloscope and I love it.

Below you can see a trace from the Z80 Clock PIN 6.

Z80 pin 6 Clock.jpg

Thanks! Found some now 👍

After some reading on the forum i checked out the icompplus.com site and ordered some chips. Also ordered the dandanator.

Don't forget to clean the expansion port before using the Dandanator. I use an old ink eraser and then some  isopropanol cleaning fluid.

Thanks! Looks like I'll have to wait a few weeks now, mail is very slow these days.

Any experience with the icompplus site for Amstrad parts?

No sorry never used icompplus.

Quote from: oyshals on 18:42, 20 February 23Any experience with the icompplus site for Amstrad parts?

I remember that someone on this forum bought some ICs from them and confirmed they are legit. Try a search on the forum or maybe better with Google as the search does not find all posts at the moment. 

Quote from: eto on 09:54, 24 February 23

Quote from: oyshals on 18:42, 20 February 23Any experience with the icompplus site for Amstrad parts?

I remember that someone on this forum bought some ICs from them and confirmed they are legit. Try a search on the forum or maybe better with Google as the search does not find all posts at the moment.

Thanks, I actually found the thread on the forum, but I couldn't find any conclusion on wether they worked or not, he seemed to stop posting. I've recieved the gate array, and it looks legit, with Amstrad part number and everything. I'm still waiting for some parts and the Dandinator I ordered for diagnostics before I can test it. I will let you know how it turns out. I reckon if this actually is legit, it will save alot of Amstrads, as they seem to have just about everything. :) 

This is the thread I meant including the conclusion that they are legit: 
https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/gate-array-decapped!/msg219511/#msg219511

Quote from: eto on 10:12, 24 February 23This is the thread I meant including the conclusion that they are legit:
https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/gate-array-decapped!/msg219511/#msg219511

Thanks! That's a relief! I've also ordered the FAL chip on that site, as I managed to break some pins, will try to fix the old one too though.

Hi,

Regarding icompplus , I've just ordered a couple of chips and some capacitors form them. I'm based in Barcelona, they are located in Madrid, so I expect to have these goods early next week. I don't exepct to have any issues, they look dependable.
If you are interested I'll post my experience.

i grabbed some 40007 gate arrays from icompplus... they arrived within 2 weeks to australia... and the chips are genuine new old stock..

Received my Dandanator Mini Dual today, but sadly it won't boot either, same grey screen, so I'm not able to test the ram Banks.

Any ideas?

Edit: Still no reaction (beeps) while using keyboard.

I have never used a Dandanator so can't help much but user manual says

The CPC Dandanator! Mini has three buttons.

• Right button : Performs a CPC reset.

• Central button : With the button pressed during boot or reset, the cartridge is deactivated and the CPC Basic starts.

• Left button : With the button pressed during the boot or reset, an alternative software is started, by default a test rom.

Quote from: oyshals on 15:14, 02 March 23Received my Dandanator Mini Dual today, but sadly it won't boot either, same grey screen, so I'm not able to test the ram Banks.

Any ideas?

Edit: Still no reaction (beeps) while using keyboard.

The CPC beeps? So it is alive? Just the display is an issue?

Quote from: Rabs on 18:50, 02 March 23

Quote from: oyshals on 15:14, 02 March 23Received my Dandanator Mini Dual today, but sadly it won't boot either, same grey screen, so I'm not able to test the ram Banks.

Any ideas?

Edit: Still no reaction (beeps) while using keyboard.

The CPC beeps? So it is alive? Just the display is an issue?

Sadly, no beeps.

is Amstrad diagnostics installed as lower ROM and do you press the button to boot into lower ROM when you turn on the Dandanator?

Quote from: eto on 21:14, 02 March 23is Amstrad diagnostics installed as lower ROM and do you press the button to boot into lower ROM when you turn on the Dandanator?

According to the description of the Dandanator it should be installed. When I press the button while turning the computer on, the whole screen actually turns dark gray, almost black (no frame), but nothing else happens.

Is the edge connector clean?

Quote from: Rabs on 21:48, 02 March 23Is the edge connector clean?

I've cleaned it with contact cleaner and a paper towel, so it looks clean, but I'll give it another try tomorrow. Watched a video with Noel's retrolab, and he used an eraser. Will try that tomorrow.

Yes, I use an old ink eraser. I often have problems with the top of the edge connector and even when I think it is clean, I clean it again.

Cleaned the connector again with a pen eraser, but no change.

Started checking voltages again and noticed that the voltage is unstable, it varies between 4,6v and 4,9v. I guess this would give me boot problems.
Replaced the power on switch with a jumper, with no change. I suspect there might be a problem with the mother board 5v female socket, as there are some visual corrosion, and some noise from the speaker and flickering on the screen, when moving the power supply plug.
I find it very hard to clean it properly, so I searched for a new one online. I only found it on "serve-retro.co.uk", but they don't ship to Norway. Anywhere else I can get my hands on one?

Quote from: oyshals on 13:08, 03 March 23Cleaned the connector again with a pen eraser, but no change.

Started checking voltages again and noticed that the voltage is unstable, it varies between 4,6v and 4,9v. I guess this would give me boot problems.
Replaced the power on switch with a jumper, with no change. I suspect there might be a problem with the mother board 5v female socket, as there are some visual corrosion, and some noise from the speaker and flickering on the screen, when moving the power supply plug.
I find it very hard to clean it properly, so I searched for a new one online. I only found it on "serve-retro.co.uk", but they don't ship to Norway. Anywhere else I can get my hands on one?

Indeed I have had power connection problems which manifest as a grey screen, but this was on the internal header posts. Similarly, if I touched the header, I saw an impact. If you struggle to get a power socket message me. I have one sat in my draw unused.

Quote from: oyshals on 13:08, 03 March 23Cleaned the connector again with a pen eraser, but no change.

Started checking voltages again and noticed that the voltage is unstable, it varies between 4,6v and 4,9v. I guess this would give me boot problems.
Replaced the power on switch with a jumper, with no change. I suspect there might be a problem with the mother board 5v female socket, as there are some visual corrosion, and some noise from the speaker and flickering on the screen, when moving the power supply plug.
I find it very hard to clean it properly, so I searched for a new one online. I only found it on "serve-retro.co.uk", but they don't ship to Norway. Anywhere else I can get my hands on one?

My 464 power connector had to be fixed twice (once in the late 80's and another time recently). Those power sockets seem to receive quite stress. Try to reflow socket's solderings. In my case I needed to do a bridge using wire as the pads were ripped off from the PCB. Hope that could help!
I had my 464 fixed d

Quote from: Rabs on 14:43, 03 March 23

Quote from: oyshals on 13:08, 03 March 23Cleaned the connector again with a pen eraser, but no change.

Started checking voltages again and noticed that the voltage is unstable, it varies between 4,6v and 4,9v. I guess this would give me boot problems.
Replaced the power on switch with a jumper, with no change. I suspect there might be a problem with the mother board 5v female socket, as there are some visual corrosion, and some noise from the speaker and flickering on the screen, when moving the power supply plug.
I find it very hard to clean it properly, so I searched for a new one online. I only found it on "serve-retro.co.uk", but they don't ship to Norway. Anywhere else I can get my hands on one?

Indeed I have had power connection problems which manifest as a grey screen, but this was on the internal header posts. Similarly, if I touched the header, I saw an impact. If you struggle to get a power socket message me. I have one sat in my draw unused.

I'm sorry, my English isn't great, could you explain the "internal header posts" please?

Quote from: JupiterJones on 15:39, 03 March 23

Quote from: oyshals on 13:08, 03 March 23Cleaned the connector again with a pen eraser, but no change.

Started checking voltages again and noticed that the voltage is unstable, it varies between 4,6v and 4,9v. I guess this would give me boot problems.
Replaced the power on switch with a jumper, with no change. I suspect there might be a problem with the mother board 5v female socket, as there are some visual corrosion, and some noise from the speaker and flickering on the screen, when moving the power supply plug.
I find it very hard to clean it properly, so I searched for a new one online. I only found it on "serve-retro.co.uk", but they don't ship to Norway. Anywhere else I can get my hands on one?

My 464 power connector had to be fixed twice (once in the late 80's and another time recently). Those power sockets seem to receive quite stress. Try to reflow socket's solderings. In my case I needed to do a bridge using wire as the pads were ripped off from the PCB. Hope that could help!
I had my 464 fixed d

Thanks, I did that earlier today, sadly didn't help. It looks like there's corrosion inside the socket, but it's a bit difficult to reach inside to clean. Will try again later before sending a message to @Rabs

Just a little update; I was playing around with the Dandanator and the CPC, just to see what happened, since i couldn't get it to work.

What happened was that every time I connected the Dandanator, the voltage went from 4,9-4,8V to 4,5-4,6V. This made me a bit hopeful that my issue is as simple as my bad 5V socket (which I've known for a while). I'm expecting the new socket this week, so keeping my fingers crossed!

I've also been studying more posts on this forum, and I see that my symptoms very often are related to bad ram. If so, I think I have bad chips on both banks. I accidentally ordered chips and sockets twice, so I guess 32 of each should be enough 😅

I also have a new Z80, CRTC, FAL, 40010, 40015 and 40025, so I should have most of what I need.

I know, why didn't I just put this money in a tested CPC from eBay? This one is MINE, probably the best Christmas gift ever! Another one just wouldn't be the same.
Also, I'd like to learn.
When i finally make it, I'll probably try to get my hands on a 464 or 664 on eBay 😊

So now I'm just waiting for the socket to arrive, I'll start with that as it is the only issue I've confirmed so far.

Thank you all for your patience and answering all my questions so far, I guess more will come!

@Rabs Thank you for offering a socket, but since I found new sockets on eBay, I didn't want to violate your private stock as you may need it on a later occasion 😊

So I received my new power supply socket. Unfortunately, it didn't resolve the main issue. However I now have stable voltage.

I've eliminated the Z80, the fal chip and the gate array.

So, two questions: If all my ram chips on both banks have died of old age, could this prevent loading the diagnostic tool on my dandanator?

I will now order an oscilloscope. Would one with a range of 5hz be sufficient?

Quote from: oyshals on 09:32, 17 March 23So I received my new power supply socket. Unfortunately, it didn't resolve the main issue. However I now have stable voltage.

I've eliminated the Z80, the fal chip and the gate array.

So, two questions: If all my ram chips on both banks have died of old age, could this prevent loading the diagnostic tool on my dandanator?

I will now order an oscilloscope. Would one with a range of 5hz be sufficient?

First question: I think so. CRT builds image from memory using some multiplexers in between. However I think it is unlikely all chips failing at once unless some really bad power supply has been connected.

Second question: Any two-channel o'scope from 40MHz and 250MSamples should do to check lines. Crystal in CPC is 16MHz, CPU clock 4MHz so going to more than 50MHz will make you pay more (but wel, I've got a cheapo Hantek at 200MHz, but for price it was a bargain).

Quote from: JupiterJones on 11:56, 17 March 23

Quote from: oyshals on 09:32, 17 March 23So I received my new power supply socket. Unfortunately, it didn't resolve the main issue. However I now have stable voltage.

I've eliminated the Z80, the fal chip and the gate array.

So, two questions: If all my ram chips on both banks have died of old age, could this prevent loading the diagnostic tool on my dandanator?

I will now order an oscilloscope. Would one with a range of 5hz be sufficient?

First question: I think so. CRT builds image from memory using some multiplexers in between. However I think it is unlikely all chips failing at once unless some really bad power supply has been connected.

Second question: Any two-channel o'scope from 40MHz and 250MSamples should do to check lines. Crystal in CPC is 16MHz, CPU clock 4MHz so going to more than 50MHz will make you pay more (but wel, I've got a cheapo Hantek at 200MHz, but for price it was a bargain).

Thanks!

Quote from: oyshals on 12:12, 15 February 23I'm sorry that I'm a bit messy, just trying to check everything.

When studying the back side of the mother board, i noticed that the color of the solderings for IC112 is a bit yellow-ish. It looks more like heat than corrosion. From the schematics, the IC112 seems to be connected to the 16MhZ clock signal, and this signal is good. Is this something to look into?

As pointed by Rabs it may be some flux residue. clean it with isopropilic alcohol, or common alcohol if you don't have IPA at hand.
IC112 is an OR gate used to drive reads and writes to PIO (8255). If I'm not wrong it should not have influence in booting the system (at least to get the blue welcome screen).

In the case of the Diagnostics ROM, which you should be booting the Dandator up as, then you don't need working RAM as it is providing diagnostics on the RAM. But you will need a working z80, GateArray and CRTC, and any supporting logic. Oh and a good expansion port connection. @Bryce would be able to confirm.

What are you seeing now with and without the Dandanator, I have lost track.

Quote from: Rabs on 12:20, 17 March 23In the case of the Diagnostics ROM, which you should be booting the Dandator up as, then you don't need working RAM as it is providing diagnostics on the RAM. But you will need a working z80, GateArray and CRTC, and any supporting logic. Oh and a good expansion port connection. @Bryce would be able to confirm.

What are you seeing now with and without the Dandanator, I have lost track.

I still have the grey screen and black frame, with and without the Dandanator connected. With the Dandanator connected, the grey "square" moves rapidly from top to bottom. When I adjust the knob on the back of the monitor, it centers on my screen.
When I push the left button (the one for diagnostics) on the Dandanator while turning the computer on, the whole screen turns dark Grey (no frame). No reaction while pressing "del" on keyboard.

I don't have a Dandator or know about its inner workings, so I can't comment on that. Regarding the RAM, it's not as some may assume, ie: 8 chips with 8k bytes per chip. Each chip stores just 1bit of each of the 64k of bytes. So if just one RAM chip fails, the entire 64k bank has failed.

Regarding scopes: 5MHz is completely pointless for most things other than analogue audio work. The bandwidth should ideally be around 5x the highest frequency you intend to measure. So for the CPC 5x16 = 80MHz, but you can get away with a 50Mhz scope for most retro related work.

Bryce.

Quote from: Rabs on 12:20, 17 March 23In the case of the Diagnostics ROM, which you should be booting the Dandator up as, then you don't need working RAM as it is providing diagnostics on the RAM. But you will need a working z80, GateArray and CRTC, and any supporting logic. Oh and a good expansion port connection. @Bryce would be able to confirm.

What are you seeing now with and without the Dandanator, I have lost track.

Hi @Rabs, you are right. If no RAM chip is healthy Noel's test will show a red pattern and numbers in screen. If this doesn't even show, then either Z80, the VDU or/and the gate array are faulty, or even the glue logic (IC110 and IC112 at least).

Quote from: Bryce on 12:40, 17 March 23I don't have a Dandator or know about its inner workings, so I can't comment on that. Regarding the RAM, it's not as some may assume, ie: 8 chips with 8k bytes per chip. Each chip stores just 1bit of each of the 64k of bytes. So if just one RAM chip fails, the entire 64k bank has failed.

Regarding scopes: 5MHz is completely pointless for most things other than analogue audio work. The bandwidth should ideally be around 5x the highest frequency you intend to measure. So for the CPC 5x16 = 80MHz, but you can get away with a 50Mhz scope for most retro related work.

Bryce.

If you have the chance, Noel explains in this video some inner insight of the diagnostics ROM, besides solving an issue with the disk drive. Maybe that would help: https://www.youtube.com/watch?v=tw0ClciNUDQ

I have been running so tests on my 664. Maybe this will help.

First I measured the 3 signals I have seen people look at to get a general idea of the state of play, clock, M1 and the VSNC on the CRTC (pin 40).

CLCK and M1
Z80 CLK AND M1.jpg

VSNC 
CRTC PIN 40 VSYNC ROM.jpg

Then I took the lower ROM out and I get a black screen and the VSNC is only at 20Hz.

CRTC PIN 40 VSYNC NO ROM.jpg

Then I remove the CRTC, and again as you would expect, a black screen.

Next I removed one of the multiplexers and this time I got a black border and grey screen. Same as you.

20230317_180338.jpg

What I don't know is what happens when I remove one of the RAM ICs and whether you get the same or a grey screen and grey border. That maybe the next test.

Now I now removing ICs may not be the same as a failure but maybe it helps, maybe not.

Quote from: Rabs on 19:36, 17 March 23I have been running so tests on my 664. Maybe this will help.

First I measured the 3 signals I have seen people look at to get a general idea of the state of play, clock, M1 and the VSNC on the CRTC (pin 40).

CLCK and M1
[url="https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39009;type=preview;file"]Z80 CLK AND M1.jpg[/url]

VSNC
[url="https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39011;type=preview;file"]CRTC PIN 40 VSYNC ROM.jpg[/url]

Then I took the lower ROM out and I get a black screen and the VSNC is only at 20Hz.

[url="https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39013;type=preview;file"]CRTC PIN 40 VSYNC NO ROM.jpg[/url]

Then I remove the CRTC, and again as you would expect, a black screen.

Next I removed one of the multiplexers and this time I got a black border and grey screen. Same as you.

[url="https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39015;type=preview;file"]20230317_180338.jpg[/url]

What I don't know is what happens when I remove one of the RAM ICs and whether you get the same or a grey screen and grey border. That maybe the next test.

Now I now removing ICs may not be the same as a failure but maybe it helps, maybe not.

Thank you very much! I will order an oscilloscope on my next paycheck, looks like a long term project 😊 Think I will start measuring traces meanwhile! I guess changing all ram chips would be a waste without more troubleshooting first!

However, after replacing the power supply socket, I still loose a lot of voltage when connecting the Dandanator, approx 0,2v, so I probably have one or more defective IC, guess I'll need the oscilloscope to locate it.

Checking traces is not a bad idea. You may find a faulty track, you never know. I had several on my 664 but the  PCB was in a bad way.

Thanks @Rabs My board appears in good condition but i have read in another thread that damaged traces aren't always visible so no harm in checking.

"Nice" to see a familiar screen, this gives me hope that it's fixable, I think your pictures will help a lot once I get the oscilloscope. The sad thing is shipping time these days😫

BTW, sometimes, it sometimes starts with a yellow or pixeled screen, still with the frame, but I'm pretty sure this comes from me touching/moving the board while working on it.

Your post gave me the urge to recheck everything, so I started with the thermal camera. The Z80 with 60 degrees Celsius, the CRTC with 50 and the fal with 45 degrees stands out, so whatever is wrong is probably causing these chips to work harder. Also noted that all 16 ram chips measures an even 30 degrees, an my 4 MUX chips is barely over room temperature, approx 20 degrees.
The z80 and fal chip are new, and shows the same as the old ones, so my guess is that they are ok. Have a new CRTC, but will wait until I know more before replacing.
@WacKEDmaN also suggested MUX earlier, so I will track down some new ones.

I also checked the clock signals, and followed their traces. Seems to be good. I know that I need an oscilloscope to be sure, but for "fun", I checked the VSync fro the CRTC, and it shows 50hz.

I should probably take a break and clear my head while waiting for proper equipment, but I guess I'll keep tinkering.

I'm really impressed with the effort you people put in to help others, so again, thank you very much!

Edit: When starting with the Dandanator in diagnostics mode (holding left button) I seem to loose the 16Mhz clock on the GA, in addition to the voltage dropping by 0,2v. That would explain the screen turning black/dark grey... I think something is using a lot of power...

In the interest of science and because I wanted to find out, I removed one RAM IC and got the same grey screen black border. So either a multiplexer failure or single RAM IC can give the grey screen.

I also repeated the tests with the Diagnostics ROM. Note, I replaced the lower ROM on the PCB of my 664,  as I do not have a Dandanator.

So with one RAM IC removed I get this.

Ram removed.jpg

And with one multiplexer remove, I get this.

Mux removed.jpg

So I do not know why your Dandanator is not working.

I guess that if you have a grey screen the Gate Array is running, the Z80 is running and reading the ROM  to setup the CRTC, which is also running. If any one of these was not running the screen would be black.

Hope this helps.

Thanks, think that'll be helpful! Just ordered 4 MUX chips from icompplus.

Next step will be re-learning how to use the oscilloscope when it arrives, before I start desoldering.

Has anyone experienced any problems with the 5v power supply on the monitor due to old age?

I tend to use a bench power supply when testing, just in case. So sorry can't comment on the CRT. But the 664 I restored did exhibit a grey screen also but this turned out to be a bad joint on the power header pins (oddly not the power connector). Reflowed the pins on the header and this solved the problem. Guess one symptom can have many root causes  :) .

Quote from: Rabs on 16:50, 18 March 23I tend to use a bench power supply when testing, just in case. So sorry can't comment on the CRT. But the 664 I restored did exhibit a grey screen also but this turned out to be a bad joint on the power header pins (oddly not the power connector). Reflowed the pins on the header and this solved the problem. Guess one symptom can have many root causes  :) .

That's what I've learned lately 😅 I will try to monitor the voltage as I flip the switch next time, to see if I have a drop as it tries to boot 👍

Measured the current it draws from the power supply, came out at 1,08 amps, seems ok according to Noel's Retrolab.

Tested with new power supply, same result, will leave it now until I recieve my oscilloscope. Getting frustrated, but not giving up.

I still don't understand why the Lower Diagnostics ROM is not asserting on your Dandanator. The fact that you get a grey screen still implies to me that the standard Lower ROM on the CPC is still running. Also the fact that you get a grey screen and not a black screen implies to me that the Z80 is running, reading the Lower ROM, initializing the CRTC and hence the GA is running. I know you have cleaned the edge connector but I have had spurious faults with one of my CPCs and even now sometimes the ROMs do not assert and I have to re-attached the ROM Board. I found it difficult (not conclusive) to just check the PCB edge connector continuity and in the end used an actual edge connector and checked from there (i.e. checked what the connecting board would see).

Quote from: Rabs on 08:50, 01 April 23I still don't understand why the Lower Diagnostics ROM is not asserting on your Dandanator. The fact that you get a grey screen still implies to me that the standard Lower ROM on the CPC is still running. Also the fact that you get a grey screen and not a black screen implies to me that the Z80 is running, reading the Lower ROM, initializing the CRTC and hence the GA is running. I know you have cleaned the edge connector but I have had spurious faults with one of my CPCs and even now sometimes the ROMs do not assert and I have to re-attached the ROM Board. I found it difficult (not conclusive) to just check the PCB edge connector continuity and in the end used an actual edge connector and checked from there (i.e. checked what the connecting board would see).

I don't know if this is relevant, but actually when I try to activate the diagnostics rom on the Dandanator the screen turns black. (I think I wrote "dark grey" earlier, but it's close to black, and no frame.) Maybe something is wrong with my Dandanator?

Edit: My voltage also drops by 0,2V when activating the Dandanator.

Screenshot_20230403-150824.png

Recently I've been getting more of this, in different colors, especially after replacing the 5v socket.
Especially when I haven't turned the CPC on for a while. This changes back to grey when touching or moving the board. I suspect some bad soldering when replacing the socket.

Look familiar to anyone?

Quote from: oyshals on 07:54, 03 April 23

Quote from: Rabs on 08:50, 01 April 23I still don't understand why the Lower Diagnostics ROM is not asserting on your Dandanator. The fact that you get a grey screen still implies to me that the standard Lower ROM on the CPC is still running. Also the fact that you get a grey screen and not a black screen implies to me that the Z80 is running, reading the Lower ROM, initializing the CRTC and hence the GA is running. I know you have cleaned the edge connector but I have had spurious faults with one of my CPCs and even now sometimes the ROMs do not assert and I have to re-attached the ROM Board. I found it difficult (not conclusive) to just check the PCB edge connector continuity and in the end used an actual edge connector and checked from there (i.e. checked what the connecting board would see).

I don't know if this is relevant, but actually when I try to activate the diagnostics rom on the Dandanator the screen turns black. (I think I wrote "dark grey" earlier, but it's close to black, and no frame.) Maybe something is wrong with my Dandanator?

Edit: My voltage also drops by 0,2V when activating the Dandanator.

You should hear a beep before the RAM test runs.

Quote from: oyshals on 14:15, 03 April 23[url="https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39149;type=preview;file"]Screenshot_20230403-150824.png[/url]

Recently I've been getting more of this, in different colors, especially after replacing the 5v socket.
Especially when I haven't turned the CPC on for a while. This changes back to grey when touching or moving the board. I suspect some bad soldering when replacing the socket.

Look familiar to anyone?

Sounds like you need to check traces and reflow connections.

Quote from: Rabs on 20:43, 04 April 23

Quote from: oyshals on 14:15, 03 April 23Screenshot_20230403-150824.png (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39149;type=preview;file)

Recently I've been getting more of this, in different colors, especially after replacing the 5v socket.
Especially when I haven't turned the CPC on for a while. This changes back to grey when touching or moving the board. I suspect some bad soldering when replacing the socket.

Look familiar to anyone?

Sounds like you need to check traces and reflow connections.

Started working on that today, also replaced two MUX chips with sockets and new chips, just to practice my soldering skills, not pretty, but seemed to work. Will buy a smaller soldering pen though 😅

I can't seem to leave this alone while waiting for my oscilloscope 😅

I've reflowed most of the 5v connections, also replaced and socketed all four MUX chips.

Still having issues with the voltage (I think), 4,5 to 4,8v. If this was larger electric plant, I would suspect the warmest components, like the z80, FAL, gate array and CRTC for drawing to much current, or maybe most of my capacitators have dried out? (Z80, GA and FAL are brand new)

I think I will have a look at installing Noel's diagnostics on my Dandanator as I'am starting to suspect that the diagnostic tool is not there or something is wrong with it...

I have more or less concluded that the diagnostics rom on my Dandanator is not working, as when I push the diagnostic button when starting, the screen turns blank/black/dark grey with no frame. After reading almost all relevant posts on the forum, this means I am not able to initialize that specific rom.

So yesterday I started desoldering chips on the right ram bank (bank 0). I have new sockets and chips, but seems like the easiest way due to spacing is to remove all of the chips.

Edit: Have been running the board with external power supply, and now have 5v all over, and 1amp. Guess the power supply from the monitor is a bit old and dodgy.

Desoldering one or two a day to not get tired and break something. So patience is key.

Quote from: oyshals on 20:20, 06 April 23I can't seem to leave this alone while waiting for my oscilloscope 😅

I've reflowed most of the 5v connections, also replaced and socketed all four MUX chips.

Still having issues with the voltage (I think), 4,5 to 4,8v. If this was larger electric plant, I would suspect the warmest components, like the z80, FAL, gate array and CRTC for drawing to much current, or maybe most of my capacitators have dried out? (Z80, GA and FAL are brand new)

I think I will have a look at installing Noel's diagnostics on my Dandanator as I'am starting to suspect that the diagnostic tool is not there or something is wrong with it...

I don't have a Dandanator, but have you seen Amstrad Noob's video on loading the diag ROM?

https://www.amstrad-noob.com/2021/03/10/video-loading-amstrad-diagnostics-on-a-dandanator/ (https://www.amstrad-noob.com/2021/03/10/video-loading-amstrad-diagnostics-on-a-dandanator/)

Did you ever check whether any internal ROM pins are shorted to GND or 5V? This is a common problem and would definitely stop the Dandator from working.

Bryce.

@Rabs Have watched the video, but haven't installed Noel's diagnostics yet, as I find it strange that I can't even load the diagnostics rom.

However, things have taken a turn to the worse, as I am getting the black screen more often. This started before replacing the ram chips.

Did some measurements as @Bryce suggested, with a multimeter, and there seems to be shortages between pin 14 and 28 and several other pins on my roms 40015 and 40025.

Edit: These shortages are only present when power is on, not when the computer is turned off.

Quote from: oyshals on 19:00, 11 April 23@Rabs Have watched the video, but haven't installed Noel's diagnostics yet, as I find it strange that I can't even load the diagnostics rom.

However, things have taken a turn to the worse, as I am getting the black screen more often. This started before replacing the ram chips.

Did some measurements as @Bryce suggested, with a multimeter, and there seems to be shortages between pin 14 and 28 and several other pins on my roms 40015 and 40025.

Edit: These shortages are only present when power is on, not when the computer is turned off.

You can't measure a short when a circuit is powered.

Bryce.

Quote from: oyshals on 19:00, 11 April 23However, things have taken a turn to the worse, as I am getting the black screen more often. This started before replacing the ram chips.

Oh dear. A black screen suggests to me the CRTC is not being setup by the lower ROM. When you say "more often", it sounds like an intermittent problem. Guess you will have to re-trace your steps and re-check some basics like clock signal etc. When I socket any ICs, I always continuity check tacks to make sure I have not damaged anything in the process.

Quote from: Rabs on 16:23, 12 April 23

Quote from: oyshals on 19:00, 11 April 23However, things have taken a turn to the worse, as I am getting the black screen more often. This started before replacing the ram chips.

Oh dear. A black screen suggests to me the CRTC is not being setup by the lower ROM. When you say "more often", it sounds like an intermittent problem. Guess you will have to re-trace your steps and re-check some basics like clock signal etc. When I socket any ICs, I always continuity check tacks to make sure I have not damaged anything in the process.

Will do, also think I will receive my oscilloscope tomorrow 👍

Quote from: Rabs on 19:36, 17 March 23I have been running so tests on my 664. Maybe this will help.

First I measured the 3 signals I have seen people look at to get a general idea of the state of play, clock, M1 and the VSNC on the CRTC (pin 40).

CLCK and M1
Z80 CLK AND M1.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39009;type=preview;file)

VSNC
CRTC PIN 40 VSYNC ROM.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39011;type=preview;file)

Then I took the lower ROM out and I get a black screen and the VSNC is only at 20Hz.

CRTC PIN 40 VSYNC NO ROM.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39013;type=preview;file)

Then I remove the CRTC, and again as you would expect, a black screen.

Next I removed one of the multiplexers and this time I got a black border and grey screen. Same as you.

20230317_180338.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39015;type=preview;file)

What I don't know is what happens when I remove one of the RAM ICs and whether you get the same or a grey screen and grey border. That maybe the next test.

Now I now removing ICs may not be the same as a failure but maybe it helps, maybe not.

Received the oscilloscope now, so will start troubleshooting tomorrow, I saw that Noel's retrolab had a video in this. I think your pictures will help alot 😊 Btw, I'm back to grey screen and black frame again now, no black screen anymore (very strange). Any tips on more chips/pins I can check with the oscilloscope would be welcome 😊

Quote from: oyshals on 20:21, 12 April 23

Quote from: Rabs on 19:36, 17 March 23I have been running so tests on my 664. Maybe this will help.

First I measured the 3 signals I have seen people look at to get a general idea of the state of play, clock, M1 and the VSNC on the CRTC (pin 40).

CLCK and M1
Z80 CLK AND M1.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39009;type=preview;file)

VSNC
CRTC PIN 40 VSYNC ROM.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39011;type=preview;file)

Then I took the lower ROM out and I get a black screen and the VSNC is only at 20Hz.

CRTC PIN 40 VSYNC NO ROM.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39013;type=preview;file)

Then I remove the CRTC, and again as you would expect, a black screen.

Next I removed one of the multiplexers and this time I got a black border and grey screen. Same as you.

20230317_180338.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39015;type=preview;file)

What I don't know is what happens when I remove one of the RAM ICs and whether you get the same or a grey screen and grey border. That maybe the next test.

Now I now removing ICs may not be the same as a failure but maybe it helps, maybe not.

Received the oscilloscope now, so will start troubleshooting tomorrow, I saw that Noel's retrolab had a video in this.

Quote from: oyshals on 20:21, 12 April 23

Quote from: Rabs on 19:36, 17 March 23I have been running so tests on my 664. Maybe this will help.

First I measured the 3 signals I have seen people look at to get a general idea of the state of play, clock, M1 and the VSNC on the CRTC (pin 40).

CLCK and M1
Z80 CLK AND M1.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39009;type=preview;file)

VSNC
CRTC PIN 40 VSYNC ROM.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39011;type=preview;file)

Then I took the lower ROM out and I get a black screen and the VSNC is only at 20Hz.

CRTC PIN 40 VSYNC NO ROM.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39013;type=preview;file)

Then I remove the CRTC, and again as you would expect, a black screen.

Next I removed one of the multiplexers and this time I got a black border and grey screen. Same as you.

20230317_180338.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39015;type=preview;file)

What I don't know is what happens when I remove one of the RAM ICs and whether you get the same or a grey screen and grey border. That maybe the next test.

Now I now removing ICs may not be the same as a failure but maybe it helps, maybe not.

Received the oscilloscope now, so will start troubleshooting tomorrow, I saw that Noel's retrolab had a video in this. I think your pictures will help alot 😊 Btw, I'm back to grey screen and black frame again now, no black screen anymore (very strange). Any tips on more chips/pins I can check with the oscilloscope would be welcome 😊

Any tips on more chips/pins I can check with the oscilloscope would be welcome 😊

Noel's video's are good and he gives lots of tips. One idea, worth looking at IC112. This is a simple 7432 quad 2 input OR but it plays a role in the memory and IO.

Quote from: Rabs on 09:21, 13 April 23

Quote from: oyshals on 20:21, 12 April 23

Quote from: Rabs on 19:36, 17 March 23I have been running so tests on my 664. Maybe this will help.

First I measured the 3 signals I have seen people look at to get a general idea of the state of play, clock, M1 and the VSNC on the CRTC (pin 40).

CLCK and M1
Z80 CLK AND M1.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39009;type=preview;file)

VSNC
CRTC PIN 40 VSYNC ROM.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39011;type=preview;file)

Then I took the lower ROM out and I get a black screen and the VSNC is only at 20Hz.

CRTC PIN 40 VSYNC NO ROM.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39013;type=preview;file)

Then I remove the CRTC, and again as you would expect, a black screen.

Next I removed one of the multiplexers and this time I got a black border and grey screen. Same as you.

20230317_180338.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39015;type=preview;file)

What I don't know is what happens when I remove one of the RAM ICs and whether you get the same or a grey screen and grey border. That maybe the next test.

Now I now removing ICs may not be the same as a failure but maybe it helps, maybe not.

Received the oscilloscope now, so will start troubleshooting tomorrow, I saw that Noel's retrolab had a video in this.

Quote from: oyshals on 20:21, 12 April 23

Quote from: Rabs on 19:36, 17 March 23I have been running so tests on my 664. Maybe this will help.

First I measured the 3 signals I have seen people look at to get a general idea of the state of play, clock, M1 and the VSNC on the CRTC (pin 40).

CLCK and M1
Z80 CLK AND M1.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39009;type=preview;file)

VSNC
CRTC PIN 40 VSYNC ROM.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39011;type=preview;file)

Then I took the lower ROM out and I get a black screen and the VSNC is only at 20Hz.

CRTC PIN 40 VSYNC NO ROM.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39013;type=preview;file)

Then I remove the CRTC, and again as you would expect, a black screen.

Next I removed one of the multiplexers and this time I got a black border and grey screen. Same as you.

20230317_180338.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39015;type=preview;file)

What I don't know is what happens when I remove one of the RAM ICs and whether you get the same or a grey screen and grey border. That maybe the next test.

Now I now removing ICs may not be the same as a failure but maybe it helps, maybe not.

Received the oscilloscope now, so will start troubleshooting tomorrow, I saw that Noel's retrolab had a video in this. I think your pictures will help alot 😊 Btw, I'm back to grey screen and black frame again now, no black screen anymore (very strange). Any tips on more chips/pins I can check with the oscilloscope would be welcome 😊

Any tips on more chips/pins I can check with the oscilloscope would be welcome 😊

Noel's video's are good and he gives lots of tips. One idea, worth looking at IC112. This is a simple 7432 quad 2 input OR but it plays a role in the memory and IO.

Thanks!
After trying my oscilloscope for the first time, my VSync and clck on the z80 seems to be fine, working like your pictures. However, the M1 on the z80 seems to be dead 🤔 This could of course be due to my limited experience with the oscilloscope. Will investigate.

As long as the VSync is at 50Hz, then I suspect it is being initialized by the lower ROM. When I removed the ROM it was only 20Hz. There is some debate on whether any VSync would be generated if not initialized but guess it may depend on the type of CRTC, mine was type 2.

I did not show you this previously but when I removed one of the multiplexers, on one occasion, I got this screen. This looks like one you posted but yours was green.

20230218_115919.jpg

Quote from: Rabs on 17:26, 13 April 23As long as the VSync is at 50Hz, then I suspect it is being initialized by the lower ROM. When I removed the ROM it was only 20Hz. There is some debate on whether any VSync would be generated if not initialized but guess it may depend on the type of CRTC, mine was type 2.

I did not show you this previously but when I removed one of the multiplexers, on one occasion, I got this screen. This looks like one you posted but yours was green.

[url="https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39206;type=preview;file"]20230218_115919.jpg[/url]

Thanks! At last I found a signal at the M1 on my Z80, but it was only at 300mV, and didn't look at all like yours, so I'm guessing it's dead.

Might change back to my old Z80 now that I've replaced the MUX and RAM chips.

Haven't had the time to follow the troubleshooting video from Noel's Retrolab yet, hoping to do that today.

Could be just a bad contact with your probe. Make sure the pin is clean where you make contact. Or check some of the other signals like MREQ for activity.  Because if you are getting 50Hz on the VSync then I guess the Z80 is running and is reading the lower ROM.

Quote from: oyshals on 20:21, 12 April 23

Quote from: Rabs on 19:36, 17 March 23I have been running so tests on my 664. Maybe this will help.

First I measured the 3 signals I have seen people look at to get a general idea of the state of play, clock, M1 and the VSNC on the CRTC (pin 40).

CLCK and M1
Z80 CLK AND M1.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39009;type=preview;file)

VSNC
CRTC PIN 40 VSYNC ROM.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39011;type=preview;file)

Then I took the lower ROM out and I get a black screen and the VSNC is only at 20Hz.

CRTC PIN 40 VSYNC NO ROM.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39013;type=preview;file)

Then I remove the CRTC, and again as you would expect, a black screen.

Next I removed one of the multiplexers and this time I got a black border and grey screen. Same as you.

20230317_180338.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39015;type=preview;file)

What I don't know is what happens when I remove one of the RAM ICs and whether you get the same or a grey screen and grey border. That maybe the next test.

Now I now removing ICs may not be the same as a failure but maybe it helps, maybe not.

Received the oscilloscope now, so will start troubleshooting tomorrow, I saw that Noel's retrolab had a video in this. I think your pictures will help alot 😊 Btw, I'm back to grey screen and black frame again now, no black screen anymore (very strange). Any tips on more chips/pins I can check with the oscilloscope would be welcome 😊

As this seems to be your first scope, you should spend a few days testing known signals on another device to practice how to use a scope properly before you start making assumptions from bad readings / wrongly setup scope.

Bryce.

Quote from: Bryce on 14:43, 14 April 23

Quote from: oyshals on 20:21, 12 April 23

Quote from: Rabs on 19:36, 17 March 23I have been running so tests on my 664. Maybe this will help.

First I measured the 3 signals I have seen people look at to get a general idea of the state of play, clock, M1 and the VSNC on the CRTC (pin 40).

CLCK and M1
Z80 CLK AND M1.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39009;type=preview;file)

VSNC
CRTC PIN 40 VSYNC ROM.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39011;type=preview;file)

Then I took the lower ROM out and I get a black screen and the VSNC is only at 20Hz.

CRTC PIN 40 VSYNC NO ROM.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39013;type=preview;file)

Then I remove the CRTC, and again as you would expect, a black screen.

Next I removed one of the multiplexers and this time I got a black border and grey screen. Same as you.

20230317_180338.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39015;type=preview;file)

What I don't know is what happens when I remove one of the RAM ICs and whether you get the same or a grey screen and grey border. That maybe the next test.

Now I now removing ICs may not be the same as a failure but maybe it helps, maybe not.

Received the oscilloscope now, so will start troubleshooting tomorrow, I saw that Noel's retrolab had a video in this. I think your pictures will help alot 😊 Btw, I'm back to grey screen and black frame again now, no black screen anymore (very strange). Any tips on more chips/pins I can check with the oscilloscope would be welcome 😊

As this seems to be your first scope, you should spend a few days testing known signals on another device to practice how to use a scope properly before you start making assumptions from bad readings / wrongly setup scope.

Bryce

Yes, i noticed that, been over 20 years since last time I used one 😊

Yesterday, I put back my old Z80 and Gate Array. Now I seem to have all the signals I need, including the M1, following Noel's video. My old Z80 doesn't get as hot as the new one I bought, so I think I might have gotten a bad Z80. The startup is also more stable, no black screen, only the old grey square and black frame.

The hottest components are now the PAL and the CRTC. Almost like they are working overtime.

Noticed that when i touched the video contact for the screen, the grey square turned yellow, so will continue reflowing solderings.

Also checked all tracks between RAM/PAL/MUX/GA/Z80, will continue with this.

Will also try to install Noel's diagnostics on the Dandanator as the one installed won't initialize, still black screen.

This would be a good time to now check all data and address lines from the ROMs for shorts to GND or VCC (while the computer is disconnected from the power).

Bryce.

Quote from: Bryce on 11:16, 15 April 23This would be a good time to now check all data and address lines from the ROMs for shorts to GND or VCC (while the computer is disconnected from the power).

Bryce.

I think you were right, this might have been a good time to check that.

I found shorts between following pins:

40015: pin 1, 14 (gnd), 27, 28 (vcc) (all together)

40025: pin 14 (gnd) and 28 (vcc)

When noticing this, I measured a couple of other chips, 5v to gnd, and they were also shorted.

It gets more interesting: I disconnected the "aux" contact for the screen, and measured short between pin 28 (vcc), 27 and 1 on the 40015. Everything on 40025 was ok.

The first time i measured a couple of weeks ago, the screen was not connected, so guess I got a bit confused.

Edit: After looking at the diagram including the 40015, it seems that pin 1, 27 and 28 are all connected to 5v. So no progress.

After finding no shorts in the ROM chips, I decided to give the Dandanator another try. Sadly it looks like the Dandanator depends on you being able to boot it on the Amstrad even to load the diganostics into it from the PC. But something on my CPC seems to be "blocking" it from initializing rendering it pretty useless at the moment.

Just to provoke a reaction from my CPC, I tried to remove the FAL, RAM chips, and MUX chips (one at the time). But sadly no reaction, still the framed grey screen.

Will keep reflowing solderings and measuring tracks, but I'm starting to think that the only solution will be replacing every IC one by one.

Sorry for all the updates, I know it may be annoying 😊

If there is a short in one of the (ROM) chips, the Dandanator can't start as a data or address pin will always be high/low.

Instead of looking for pure shorts you could also check the resistance between a pin and VCC or GND. I once had the situation, that most pins had very high resistance (>100K) and one pin had (I think) around 400Ohms. When turned on the pin of the IC was not working correctly and was putting a constant high (or low) signal on the bus. As a result, nothing will work. Not the internal stuff and also no external add-on like the Dandanator. 

Btw: If you remove the ROM chips, you can try again with the Dandanator. If it was indeed a short in the ROM, diagnostics should finally boot as it doesn't need the internal ROM.

Quote from: eto on 20:38, 16 April 23If there is a short in one of the (ROM) chips, the Dandanator can't start as a data or address pin will always be high/low.

Instead of looking for pure shorts you could also check the resistance between a pin and VCC or GND. I once had the situation, that most pins had very high resistance (>100K) and one pin had (I think) around 400Ohms. When turned on the pin of the IC was not working correctly and was putting a constant high (or low) signal on the bus. As a result, nothing will work. Not the internal stuff and also no external add-on like the Dandanator.

Btw: If you remove the ROM chips, you can try again with the Dandanator. If it was indeed a short in the ROM, diagnostics should finally boot as it doesn't need the internal ROM.

Thanks!
I actually found something like that now, pin 22 only has 3,6k ohms to the vcc (pin 28) on the 40025 🤔 

Not sure if this is normal as it is connected  via r112 (2,2k ohms) to gnd according to the schematics. Resistance to gnd is correct. Measured on my new 40025, an there was "infinite" resistance. But again, the new one is not attached to a board...

Nothing found on 40015 for now.

Think pin 22 (OE) is pulled low via the 2.2k resistor. This is also connected to edge connector pin 43  (ŔOMDIS) and I guess is pulled high when the Dandanator replaces the Lower ROM with the Diag ROM.

If you need me to check any signals by way of comparison just let me know.

Is there anyway you can check continuity on the edge connector?

Quote from: Rabs on 22:11, 16 April 23Think pin 22 (OE) is pulled low via the 2.2k resistor. This is also connected to edge connector pin 43  (ŔOMDIS) and I guess is pulled high when the Dandanator replaces the Lower ROM with the Diag ROM.

If you need me to check any signals by way of comparison just let me know.

Is there anyway you can check continuity on the edge connector?

Thanks, I might take you up on that offer, but right now, I'm not sure which signals I should be looking for. After alot of studying and checking, both on the forum, videos and on the board itself, this doesn't seem to be a ram issue, and the z80, CRTC, fal, mux and gate array seems to working. Comparing to most of what I've been reading, everything seems ok, but still not working 🤔 I've also been unable to find any "unusual" shorts.
So now it's a bit difficult to say where to start.

Btw, you were correct on the pin 22, high with Dandanator connected, and low when not.

I assume you have watched Noel's video.


Interesting that he suggests to test any ICs in a known working CPC.

Quick check with you, are these correct?
CLK OK
M1 OK
VSYNC OK
HSYNC ?

Do you have a speaker attached?
Do you hear a BEEP when the Dandanator runs the Diag ROM.

The plan was actually to get another one anyway, because this one I'm planning to give back to my older brother as a Christmas present (a bit of childhood nostalgia as we got i from our dad over 30 years ago), but I think you are right, I'll have to go on eBay earlier than planned 😊

Those signals seemed correct according to his other videos, but in those videos, he only looked for "traffic", as in this one he shows me the signals more clearly, so I will check again.

I don't get any beep when connecting the Dandanator at the moment. With the two "normal" roms (for games), it gives the same framed grey screen, but when trying to initialize the diagnostic rom, the screen turnus black.

Thank you for this video, don't know why I haven't seen it yet. And thank you for your patience!

If I could bother you to post a picture of the interrupt signal on the z80, I would be grateful.
I think mine is locked at low. And also maybe the hsync and VSync signals just to be sure. I think mine are correct, but just to be sure.

Quote from: oyshals on 09:00, 17 April 23If I could bother you to post a picture of the interrupt signal on the z80, I would be grateful.
I think mine is locked at low. And also maybe the hsync and VSync signals just to be sure. I think mine are correct, but just to be sure.

Measurements taken from a working 6128 with just the READY prompt displayed.

VSYNC CRTC PIN 40 50Hz
VSYNC_CRTC_PIN_40.jpg

HSYNC CRTC PIN 39 15.62KHz
HSYNC_CRTC_PIN_39.jpg

INT GA PIN 32 (Note Frequency varies and is slow between 75Hz and 300Hz and you can miss it unless you have the scope setup to catch it, should be high most of the time). Note also this is connected to R144, which is connected to INT Z80 PIN 16.
INT_GA_PIN_32.jpg

What board revision do you have? Mine is an MC0020F. If you have one of these the schematic in the manual is different. But see this great bit of work by @pelrun CPC6128 - new schematic capture and layout for MC0020x boards (https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/cpc6128-new-schematic-capture-and-layout-for-rev1-boards/).

Have you watched this?

Quote from: Rabs on 20:45, 17 April 23Have you watched this?

Thanks, I will check the revision when I get the time.

Think I've seen it at a time I thought it wasn't relevant, will watch again.

If someone could provide me with the current draw (amps) of a working 6128 it would be very much appreciated. I've just based my thoughts on this
on something Noel said in a video, so confirmation would be great!

Think the video from Noel covers a lot of what you may be seeing.

Yes, that video was actually great! Will also make a 10th attempt at cleaning the edge socket 🙈

Current draw from power on 942mA.

Quote from: Rabs on 10:15, 18 April 23Current draw from power on 942mA.

Hmmm... Mine was above 1,1 last time I checked, will re-check.

Quote from: oyshals on 10:17, 18 April 23

Quote from: Rabs on 10:15, 18 April 23Current draw from power on 942mA.

Hmmm... Mine was above 1,1 last time I checked, will re-check.

So, I re-checked the int on my ga and z80. I had to adjust my scope to "full sensitivity" (sorry not familiar with the terms) to find anything. I was only able to find 200mV. Since I had adjusted the scope in this way, I'm guessing this is just static, so looks like it's pulled low as I can see that you have 5V. I will watch again the two last videos you posted as these explained the int signal very well.

Also noticed that I have to reflow pins on the contact for power switch. Probably because I've connected and disconnected so many times.

So yes a low INT was one of the symptoms in Noel's video.

His Diag ROM did not work because of the edge connector but you have cleaned and cleaned yours. I continue to have problems with edge connectors and often have to reseat the connector.

But assuming it is good then something is stopping the Diag ROM from running. He indicates it only depends on ROM not RAM but also refers to the data latch buffer IC114. So inference is something is corrupting the data bus. @Bryce and @eto have already suggested removing the ROMs and retrying the Dandanator. But in case somehow the latch buffer is placing RAM on the bus and as you have these socketed anyway you could try removing all RAM and retrying the Dandanator.

That's helpful I will do another try with the edge connector, and remove all chips on ram bank 0 before desoldering more.

Might be a stupid question for you with more experience, but are you suggesting removing both the 40015 and 40025 roms? And a follow up stupid question; which of these are upper and lower rom? I've seen those terms being used alot.

40015 is a 16K EPROM with AMSDOS( upper ROM #7)
40025 is a 32K EPROM with Firmware (lowerROM) in the lower 16K and BASIC (upper ROM #0) in the upper 16K

When the CPC is switched on or reset the firmware (the lower ROM) is entered at address &0000, BASIC (or other upper ROMs) will be accessed at &C000. Some logic in the CPC will make sure that the the 40025 can act as two ROMs at different addresses.  

I think @Bryce and @eto are only referring to the lower ROM, 40025, which occupies the lower address space where the DIAG ROM runs but hopefully they will correct me if wrong. But what I don't understand is, if the ROM is an issue why the CRTC is being correctly initialised in terms of HSYNC and VSYNC.

Quote from: Rabs on 12:40, 19 April 23So yes a low INT was one of the symptoms in Noel's video.

His Diag ROM did not work because of the edge connector but you have cleaned and cleaned yours. I continue to have problems with edge connectors and often have to reseat the connector.

But assuming it is good then something is stopping the Diag ROM from running. He indicates it only depends on ROM not RAM but also refers to the data latch buffer IC114. So inference is something is corrupting the data bus. @Bryce and @eto have already suggested removing the ROMs and retrying the Dandanator. But in case somehow the latch buffer is placing RAM on the bus and as you have these socketed anyway you could try removing all RAM and retrying the Dandanator.

Quote from: oyshals on 12:53, 19 April 23That's helpful I will do another try with the edge connector, and remove all chips on ram bank 0 before desoldering more.

I think you only need to worry about the lower active RAM bank.

Quote from: Rabs on 13:52, 19 April 23

Quote from: Rabs on 12:40, 19 April 23So yes a low INT was one of the symptoms in Noel's video.

His Diag ROM did not work because of the edge connector but you have cleaned and cleaned yours. I continue to have problems with edge connectors and often have to reseat the connector.

But assuming it is good then something is stopping the Diag ROM from running. He indicates it only depends on ROM not RAM but also refers to the data latch buffer IC114. So inference is something is corrupting the data bus. @Bryce and @eto have already suggested removing the ROMs and retrying the Dandanator. But in case somehow the latch buffer is placing RAM on the bus and as you have these socketed anyway you could try removing all RAM and retrying the Dandanator.

Quote from: oyshals on 12:53, 19 April 23That's helpful I will do another try with the edge connector, and remove all chips on ram bank 0 before desoldering more.

I think you only need to worry about the lower active RAM bank.

Thanks! That is the right one yes? If not, I've been wasting your time for months now 🙈

Quote from: oyshals on 13:59, 19 April 23Thanks! That is the right one yes? If not, I've been wasting your time for months now 🙈

yes, the right bank is bank 0.

However: if there is a short on any IC on bank 1, this will have the same impact as a short on bank 0. The lines are fully parallel (except for CAS). 

Quote from: Rabs on 13:30, 19 April 23I think @Bryce and @eto are only referring to the lower ROM, 40025, which occupies the lower address space where the DIAG ROM runs but hopefully they will correct me if wrong. But what I don't understand is, if the ROM is an issue why the CRTC is being correctly initialised in terms of HSYNC and VSYNC.

Both ROM's are connected in parallel for most pins, so either ROM being bad will give you problems.

Bryce.

Removed the lower rom, 40025, turned it on, and got a blank (black) screen. (as expected since there was no rom)

Connected the Dandanator and turned it on again (not pressing the diagnosis button) and got a grey screen with black frame.

Restarted with diagnosis button pressed, same as before blank/black screen. So either something is wrong with my Dandanator, or something is interrupting this specific ROM. Have both cleaned and measured the expansion port.

I'm a bit baffled. Will start measuring before putting in a socket for the lower ROM. Also maybe try replacing the socketed chips without ROM installed.

Does anyone have any information on the IC201? I can't seem to find it in the main schematics.

Mine gets very hot, and when I touch it, I get disturbance on the screen. I've reflowed all its pins.

I searched on the forum and found that this was part of the issue on two incidents with the grey screen black frame case.

According to the service manual parts list, IC201 is the upd765 floppy drive controller.

Edit: You can see the schematic of the disk controller part on page 28 of the pdf service manual, with the title "Interface Circuit Diagram".

Quote from: robcfg on 22:44, 29 April 23According to the service manual parts list, IC201 is the upd765 floppy drive controller.

Thanks. It's showing strange symptoms, and I need to add that the CPC was put away due to inability to read discs. Could be something to look into then...

Maybe the chip itself isn't bad, though if it gets super hot it's definitely a bad sign, so please check the components associated with it.

Remember, page 28 of the pdf service manual, Interface Circuit Diagram  ;)

Quote from: robcfg on 22:51, 29 April 23Maybe the chip itself isn't bad, though if it gets super hot it's definitely a bad sign, so please check the components associated with it.

Remember, page 28 of the pdf service manual, Interface Circuit Diagram  ;)

Thanks! Found it, my bad 😅

No worries mate, good luck with the repair!

Quote from: oyshals on 22:17, 29 April 23Does anyone have any information on the IC201? I can't seem to find it in the main schematics.

Mine gets very hot, and when I touch it, I get disturbance on the screen. 

@oyshals 
Also touch the 3 other chips above IC201
These are IC206 - IC203 - IC208

I had a weird fault a long time ago similar to touching chips in that area
and it turned out to be the IC203 (74HC240N)
Slide your Finger Left and Right over each chip and Observe the screen

Good luck

Keep Safe

Ray

Quote from: Audronic on 01:55, 30 April 23

Quote from: oyshals on 22:17, 29 April 23Does anyone have any information on the IC201? I can't seem to find it in the main schematics.

Mine gets very hot, and when I touch it, I get disturbance on the screen.

@oyshals
Also touch the 3 other chips above IC201
These are IC206 - IC203 - IC208

I had a weird fault a long time ago similar to touching chips in that area
and it turned out to be the IC203 (74HC240N)
Slide your Finger Left and Right over each chip and Observe the screen

Good luck

Keep Safe

Ray

Thanks! Did that and only got a reaction from ic201. I was pretty rough with the other ones, but no reaction. Will look for signals later.

I have not had problems with IC 201 the disk controller but I have with the associated logic gates (actually the tracks) which resulted in ROMDIS being asserted incorrectly when A15 was high (it actually stopped the BASIC ROM from running). It is worth checking the logic gate outputs in this area and look for any floating signals or outputs which do not match the logic inputs.

Quote from: Rabs on 13:46, 30 April 23I have not had problems with IC 201 the disk controller but I have with the associated logic gates (actually the tracks) which resulted in ROMDIS being asserted incorrectly when A15 was high (it actually stopped the BASIC ROM from running). It is worth checking the logic gate outputs in this area and look for any floating signals or outputs which do not match the logic inputs.

Thanks, I'll do that.

I also think i'll have to start over again.

I tend to loose track after a week off 🙈

I had a broken track between IC205 and IC212 on the Disk Controller side of the PCB. 

IC205 PIN 2 AND gate input was floating high, should have been held low by IC212 PIN 5.
IC205 PIN 1 AND gate input is connected to A15
IC203 PIN 3 AND gate output is connected to ROMDIS

Every time A15 went high, the ROM was disabled. 

So lower ROM worked, upper ROM was disabled. Took me a while...

Worth a check in case you have something similar as this stopped the ROM code from running.

By the way, in the end I did purchase a Dandanator. First time I plugged it in and powered on I got a grey screen black border and this is with a fully working 6128. I cleaned the edge connector and reseated the Dandanator and it worked fine. An alternative to using the Dandanator to run the Diag ROM is to just replace the lower ROM with a Diag ROM. 

Quote from: Rabs on 20:19, 30 April 23By the way, in the end I did purchase a Dandanator. First time I plugged it in and powered on I got a grey screen black border and this is with a fully working 6128. I cleaned the edge connector and reseated the Dandanator and it worked fine. An alternative to using the Dandanator to run the Diag ROM is to just replace the lower ROM with a Diag ROM.

Is there somewhere I can buy a Diagnostics rom online, or do most people make them themselves?

I'm looking seriously at buying a working 6128 from eBay for comparison as there seems to be alot of issues that could cause the grey screen.

My voltage is also somewhat unstable, sometimes as low as 4,65v and up to 4,95v, and sometimes it uses a long time starting up, which has turned my attention a bit towards dried out capacitators, but there's probably about 80 of them, so that would be quite a task. However, I've found 2 or 3 which has cracks (orange ones next to the ram banks) but no shorts in them.

The FDC (IC201) will get a little hot if the boot sequence gets stuck somewhere because the chip gets trapped in some sort of initialisation loop. I've had this a few times and more than once it was ROM 7 that had failed.

Bryce.

I socketed and replaced both the 40015 and 40025 roms tonight, sadly no difference. The new roms however has not been tested with a working computer though. Waiting for a diagnostics rom which @Rabs was kind enough to send me now.

So I started thinking that I have a shortcirquit, or almost anyways.

With board disconnected I measured between +5v and gnd on random chips, and found it to be 1,4k ohm, on some chips as low as 1,2. Seems a bit low. Can anyone confirm?

If this is the case, are there any usual suspects, or would I have to desolder chips one by one measuring?

Quote from: oyshals on 17:53, 02 May 23So I started thinking that I have a shortcirquit, or almost anyways.

With board disconnected I measured between +5v and gnd on random chips, and found it to be 1,4k ohm, on some chips as low as 1,2. Seems a bit low. Can anyone confirm?

If this is the case, are there any usual suspects, or would I have to desolder chips one by one measuring?

I think you are just measuring the parallel resistance of all devices on the board.

Thanks! I think I'll just wait for the diag rom now 😊 Thanks again for that!

Btw; Should I try to remove the three capacitators I found to be cracked? (the orange ones by the ram banks)

Sorry, I don't have any experience of failed ceramic capacitors on the CPC but they are needed to smooth the power to the IC. I would wait until you get Diagnostics ROM.

Quote from: Rabs on 19:41, 03 May 23Sorry, I don't have any experience of failed ceramic capacitors on the CPC but they are needed to smooth the power to the IC. I would wait until you get Diagnostics ROM.

Will do that, just been reflowing some solderings today, can't seem to leave it alone 😅

Thank you @Rabs for the diagnostic rom!

Sadly I haven't been able to get it to work. I actually seem to get the same symptoms as when I push the diagnostic button on the Dandanator, the screen turns black, no grey square 🤔 Almost like something is blocking any diagnostic roms from initializing.

I've fiddled alot with the board now, so I think I will start retracing my steps.

Quote from: oyshals on 22:26, 20 May 23Thank you @Rabs for the diagnostic rom!

Sadly I haven't been able to get it to work. I actually seem to get the same symptoms as when I push the diagnostic button on the Dandanator, the screen turns black, no grey square 🤔 Almost like something is blocking any diagnostic roms from initializing.

I've fiddled alot with the board now, so I think I will start retracing my steps.

I guess that this is not unexpected and proves the Dandanator is working. Can you check VSYNC again and make sure this is 50Hz. If it's not, then why is it correct when the original ROM is used? I guess the only thing you have not changed is the CRTC.

Quote from: Rabs on 22:49, 20 May 23

Quote from: oyshals on 22:26, 20 May 23Thank you @Rabs for the diagnostic rom!

Sadly I haven't been able to get it to work. I actually seem to get the same symptoms as when I push the diagnostic button on the Dandanator, the screen turns black, no grey square 🤔 Almost like something is blocking any diagnostic roms from initializing.

I've fiddled alot with the board now, so I think I will start retracing my steps.

I guess that this is not unexpected and proves the Dandanator is working. Can you check VSYNC again and make sure this is 50Hz. If it's not, then why is it correct when the original ROM is used? I guess the only thing you have not changed is the CRTC.

Will compare all signals with the original rom and with the diag rom, will also re-visit all my solderings. I actually have a new CRTC and a socket for it, so might try that one as well.

I agree, it would be a good idea to retrace your steps and check each stage. Only yesterday, I was tracking down a problem with a new board I had built for my rack based z80. I concentrated on the board itself only to find a ZIF socket on the ROM board was causing ramdom program failures. So I know one bad connection can cause havoc on the bus.

My guess is something is corrupting the bus and there are a number of devices on the bus that can do this, including RAM, AMSDOS ROM, Disk Controller and PIO.

My assumption is that if you get a VSYNC of 50Hz, that the Lower Diagnostics ROM has initialised the CRTC, which is one of the first things it does and is the distinguishing difference between a grey screen and a black screen. What I don't understand is why you get a grey screen with the standard Lower ROM and a black screen with the Diagnostics ROM.

Early on the Lower Diagnostics ROM also programs the AY sound chip to emit a beep. I guess you have never heard this?

I am also assuming that the Z80 and Gate Array are good because you have replaced these at some stage but it would be better to confirm this with a known working CPC. I am also assuming the CRTC is working because you see a grey screen and in the past a colour pattern.

I would, check the simpler 74 series logic ICs, just because this is simple to do, and make sure the logic outputs match the inputs, just incase one of these is incorrectly asserting a device on the bus.

After that I would, start with a minimal system running the Lower Diagnostic ROM and hence remove the chance of bus corruption as much as possible. So no AMSDOS ROM, no RAM, no Disk Controller and even maybe no PIO.

Maybe it just wants to die 😅 (I won't let it)

No, haven't had any beeps during my process.

I'm actually itching to try to replace the disc controller as I got a pretty strong reaction just by touching it. And because the malfunctioning disc drive was the reason it was put away 25 years ago. But I'll retrace first, as it has become a bit unstable. I think I didn't clean properly before installing sockets.

@Rabs I've got something to show you....

Quote from: oyshals on 16:34, 03 June 23@Rabs I've got something to show you....

Working?

Ok, this is embarrassing 😅 I've forgotten how to upload pictures to the forum 🙈

However, I've got news. After removing the disc controller, the diagnostic's started! First sign of life!!! However, on my screen, I've got a big, black square on the top left which I would like to post an image of here when I find out how to post it again 😅

Go to preview and add attachments 

Thanks!

Quote from: oyshals on 16:52, 03 June 23Thanks!

Oh that's an odd one, what do you have installed at the moment?

I think it's related to my bad soldering skills, think this is the time to re-visit my old work...IMG_20230603_175756.jpg

Quote from: oyshals on 17:05, 03 June 23I think it's related to my bad soldering skills, think this is the time to re-visit my old work...[url="https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39599;type=preview;file"]IMG_20230603_175756.jpg[/url]

Well done getting somewhere now  ;D

I'm having some issues with the display, suspect this might be an issue with the connector. The display issue comes and goes.

The MUX chips and poor socketing (my recent work) are also one of my suspects. Both for the display issue and the RAM issue. I've replaced the RAM chips, but the fault doesn't change. 1 and 3 working, and the rest faulty. Will address this issue when I get the time.IMG_20230603_180629.jpg

Quote from: oyshals on 20:42, 03 June 23I'm having some issues with the display, suspect this might be an issue with the connector. The display issue comes and goes.

The MUX chips and poor socketing (my recent work) are also one of my suspects. Both for the display issue and the RAM issue. I've replaced the RAM chips, but the fault doesn't change. 1 and 3 working, and the rest faulty. Will address this issue when I get the time.IMG_20230603_180629.jpg (https://www.cpcwiki.eu/forum/index.php?action=dlattach;attach=39601;type=preview;file)

Time to check all the tracks, its easy to lift a pad when desoldering. But at least you can see activity now.

@Rabs Does your Diganostics rom test ram bank 0 or 1 when it boots? Maybe I have to do the fal-trick?

Only bank 0 to start with. Only if this passes do you get to the main screen to test upper banks of RAM.

There is a github repository on Noel's diagnostic ROM for info.

In case you need it, the github page is Amstrad Diagnostics (https://github.com/llopis/amstrad-diagnostics).

If Amstrad diagnostics reports the same ICs you should check the connections of all RAM IC pins and all the MUX IC pins.

I once soldered sockets and bent one of the socket pins inwards. I didn't see that and had that one IC reporting issues. 

The same could happen if you accidentally removed a pad. Also happened once to me and the IC then was reported dead. Thankfully that could be fixed easily with a wire.

Have you soldered your 2nd RAM bank also? If not it could make sense to easily force the 6128 to use the 2nd RAM bank as the primary bank and see if the error is still present. 

Quote from: eto on 13:53, 04 June 23If Amstrad diagnostics reports the same ICs you should check the connections of all RAM IC pins and all the MUX IC pins.

I once soldered sockets and bent one of the socket pins inwards. I didn't see that and had that one IC reporting issues.

The same could happen if you accidentally removed a pad. Also happened once to me and the IC then was reported dead. Thankfully that could be fixed easily with a wire.

Have you soldered your 2nd RAM bank also? If not it could make sense to easily force the 6128 to use the 2nd RAM bank as the primary bank and see if the error is still present.

Thanks! Making some small progress. Replaced one of the sockets for the MUX today, cleaned the pads more thoroughly this time. No broken pads. Will take my time with this, babysteps.

Looking through my workshop to find wires thin enough to make the "fal-socket".

The screen issue i 90% certain to be the video connector or cable. Will try to reflow the solderings on this one later.

Been checking traces, and have replaced the MUX chips and sockets. No damage found. Having some trouble starting it, almost like it has to "warm up", will post pictures of this later. Always same result when running diagnostic, ram chip 1 and 3 working, none of the other even when swapping. Been looking in the schematics to see if there is something special with those two.

Might be a power issue though, I seem to have worn out the new power socket already, so will try to replace it again.

I'm also thinking that the disc controller caused the boot to crash, but something else corrupted the disc controller, thereby causing the crash. Thinking of maybe removing a few more of the IC's on the disc part of the board. In that case, would I still be able to initialize the diagnostic's rom?

Have you traced data out pin 14 from each RAM IC to the buffer latch IC114?

Still looks like you just have some bad traces on the data lines associated the RAM.

Will double check tomorrow, hopefully I will find something. At least I have two to compare with now 👍

Haven't given up, just taken a longer break. Will start checking capacitators when I resume, due to the "start up delay" varying voltages, and lack of broken tracks. 

Will probably be a few months yet, as I've taken on a few easier projects, restoring a few PC's I found in my parents garage. Will update when I resume work on the CPC 😊