Hi all,
I bought a 464 about 10 years ago, it was the later shorter board version. I replaced the cassette belt and all was good. I did have a DDI and an FD-1 also. I was making use of a USB charger for power. One afternoon (without the DDI/FD-1 connected) whilst part way through loading a cassette the output suddenly went black and sadly the fault remained upon a cold start. I had some time last week to finally take a look at it again, the output gave a grey screen with a black border so the first port of call was to test the RAM, I don't have a diagnostics ROM but I do have a small USB RAM tester so I removed all the 4164 RAM with my desoldering gun and hot air station before installing sockets. Happily one of the RAM chips did test bad so I returned the other 7 back into the new sockets. I have some tested 150ns 4264 RAM taken from an Atari 800XL which should be fine along with the existing 4164 but upon power up I now get the expected 464 start-up screen but the background colour is black and the machine freezes. Any idea of the likely cause? Perhaps it's not happy with that single 4264 RAM or I need to check my soldering work with the sockets. It all looked visually fine after the desoldering, no lifted traces or damaged through holes but I should likely check that first unless the symptom of a black background/freeze points to something else causing the issue. I don't own a logic probe or oscilloscope, just a basic multimeter so if there's a guide to follow some basic testing that would be handy.
thanks all!
photo?
You probably still have a bad RAM. Those testers aren't perfect and will sometimes report a chip being good, even though it's not. This is because the tester tests the chip at a very low speed. Try blind swapping each original chip with one of the XL chips and test each time.
Bryce.
Hi,
thanks for the reply. I've now tried swapping each one of the RAM with the 4264 testing the CPC as I change each one. Sadly no change. I've only got 7 spare 4264's so I had to leave one of the 4164's but I swapped a few to be sure. I have another known working 40010 gate array so I tried swapping that just in case but no change. I've put the original 4164's and 40010 back in now with the single 4264 replacing the known bad one.
I've taken a couple of photos. One of the board and one of the output but there doesn't appear to be any way to upload photos to my post only to link an image to one uploaded elsewhere online.
I suppose I will need to be doing some checks with the multimeter to each of the sockets next?
Any advice on how to progress?
thanks again.
photos you need add to post.
Quote from: Tezz on 18:35, 04 March 24I've taken a couple of photos. One of the board and one of the output but there doesn't appear to be any way to upload photos to my post only to link an image to one uploaded elsewhere online.
Click on "Reply" and then there should be the option to upload images. Or - if you clicked on "quick reply", you can click on "preview" and then the option to upload pictures appears.
Thanks, I've attached the two photos now.
I've taken the board out of the case this afternoon and double checked my soldering which all appears to be fine. I did a quick continuity check between the pins although not thorough I didn't find an issue.
I'm stumped, any advice on how to progress appreciated! thanks again
Does holding down the DEL key make a beeping sound?
Bryce.
Quote from: Bryce on 15:37, 05 March 24Does holding down the DEL key make a beeping sound?
Bryce.
Hi,
No, there's no beep when holding down the DEL key.
Whilst I was testing however I accidentally changed my TV source to a different input and when changed back to SCART the CPC's output was in colour with the correct blue background and yellow text. Cold starting it displays with a black background with white text again until I change my TV from one source back to SCART.
I also have a working long board 464 so I've just tested the keyboard just in case it was causing any issue but the keyboard is working fine with that board.
Just so, I understand, originally the CPC screen turned black part way through a tape load.
On restarting you got a black border and grey screen, classic RAM failure, so checked the RAM and indeed found one faulty IC, so replaced this with a 4264.
Now the CPC boots at least to a ready prompt but with a black background and white text and freezes?
You have retraced your steps and checked you RAM IC work.
Odd so the CPC boots to the Ready prompt and but with the wrong colour and then hangs (not responding to keyboard). I would double check the RAM and retest.
@Bryce, I think the MT4264 has a 256 cycle refresh. How does this work with the Z80 or is it not an issue?
Quote from: Rabs on 19:14, 05 March 24I think the MT4264 has a 256 cycle refresh. How does this work with the Z80 or is it not an issue?
On a Z80 system that uses the R register to refresh the RAM that would not work, however on the CPC the GateArray is responsible for the RAM refresh, which also updates bit 8 (thus uses 256 cycles).
Quote from: Rabs on 18:48, 05 March 24Just so, I understand, originally the CPC screen turned black part way through a tape load.
On restarting you got a black border and grey screen, classic RAM failure, so checked the RAM and indeed found one faulty IC, so replaced this with a 4264.
Now the CPC boots at least to a ready prompt but with a black background and white text and freezes?
You have retraced your steps and checked you RAM IC work.
Odd so the CPC boots to the Ready prompt and but with the wrong colour and then hangs (not responding to keyboard). I would double check the RAM and retest.
Hi, yes that's right except that I noticed this afternoon that when it's hung on start-up with no keyboard response that if I change the TV source off SCART and back to SCART the CPC's output is then actually in the correct colours with blue background and yellow text so the TV must not be quite getting the color signal at the point it hangs which is more encouraging.
I guess there must be an issue somewhere I've missed with my IC work. What would be the best approach to diagnose the RAM/sockets? I've done a basic continuity test between each adjacent pin for any shorts which were fine. I checked several connections between the RAM legs and the solder joints on the bottom of the board which were fine, I haven't checked anywhere near all 16 legs of the 8 IC's in this way however. The DRAM tester I'm using is the one created by Simon Raybould if anyone is familiar with that one.
Is the CPC actually hanging or is it just not responding to any keyboard input?
Is there actually a second problem with tha AY-3-8912 or 8255 PIO when scanning the keyboard matrix?
Quote from: Rabs on 21:43, 05 March 24Is the CPC actually hanging or is it just not responding to any keyboard input?
Is there actually a second problem with tha AY-3-8912 or 8255 PIO when scanning the keyboard matrix?
It looks to be hanging rather than awaiting input as the display to the TV isn't quite initialised on power up. Yesterday I swapped the Z80 from my working long board to rule that out and no change although when I then swapped the TV source from and back to SCART input the frozen (now colour) display is shifted to the left. I did some more basic checks with the multimeter around the RAM following traces from the RAM legs to where the traces went to and all checked out. I checked continuity of most of the RAM legs to the solder joints on the bottom of the board and all looks fine there too. Perhaps one of the LS logic chips has failed? Any advice on how to progress with the diagnosis? Thanks :D
My next check would be the 40009 ROM. Check if it has any stuck Data or Address bits.
Bryce.
Quote from: Bryce on 14:22, 07 March 24My next check would be the 40009 ROM. Check if it has any stuck Data or Address bits.
Bryce.
OK thanks, I'll look into that. I'm missing an oscilloscope to look at the current state but I did recently buy a TL866II Plus which I've not yet used so I could remove the ROM and check that it's ok along with the 74LS logic although from what I've read testing logic with the TL866II is not conclusive as to whether it is fully operational. It would be nice to have something like SLICE to use but £450 is a bit pricey. It's a shame there's nothing like the old Fluke 9010A functionality around today. I've always taken the lamers approach removing IC's until I find the culprit.
Screen has "Ready" and currsor. Firmware and proc in bank 2 ram work. Check joy port or Simulate press key beetwen AY and 147
When you join LS145 pin 15 to expansion port pin 1 (sound) you hear in speaker brum 50hz scan keyboard. This is check that's interrupt and soft and z80 works fine.
Oscylosphone is in CPC :-D
Quote from: McArti0 on 16:41, 08 March 24Screen has "Ready" and currsor. Firmware and proc in bank 2 ram work. Check joy port or Simulate press key beetwen AY and 147
Thanks for the info, that's good to know. Could you explain which pin of the AY and where 147 is on the board to simulate a key press.
Quote from: McArti0 on 17:29, 08 March 24When you join LS145 pin 15 to expansion port pin 1 (sound) you hear in speaker brum 50hz scan keyboard. This is check that's interrupt and soft and z80 works fine.
Oscylosphone is in CPC :-D
Great, thanks I'll definately try that over the weekend.
https://www.cpcwiki.eu/imgs/6/6d/Schaltplan_cpc_464.jpg
This is LS145 not 147. My error.
Sound is at left side resistor R114 too. Its nearest LS145.
On schem you can look how keyboard work.
Quote from: McArti0 on 18:55, 08 March 24https://www.cpcwiki.eu/imgs/6/6d/Schaltplan_cpc_464.jpg
This is LS145 not 147. My error.
Sound is at left side resistor R114 too. Its nearest LS145.
On schem you can look how keyboard work.
Great, thanks very much for that. I'll look forward to making some progress with the board over the weekend.
Quote from: Tezz on 15:45, 08 March 24Quote from: Bryce on 14:22, 07 March 24My next check would be the 40009 ROM. Check if it has any stuck Data or Address bits.
Bryce.
OK thanks, I'll look into that. I'm missing an oscilloscope to look at the current state but I did recently buy a TL866II Plus which I've not yet used so I could remove the ROM and check that it's ok along with the 74LS logic although from what I've read testing logic with the TL866II is not conclusive as to whether it is fully operational. It would be nice to have something like SLICE to use but £450 is a bit pricey. It's a shame there's nothing like the old Fluke 9010A functionality around today. I've always taken the lamers approach removing IC's until I find the culprit.
I use a Hantek DSO5102P oscilloscope. Makes investigating a lot simpler.
See https://www.amazon.co.uk/gp/product/B00I5EWF1U/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
This is me checking keyboard scan pulses out of the 8255.
20240128_175445.jpg
Quote from: McArti0 on 16:41, 08 March 24Screen has "Ready" and currsor. Firmware and proc in bank 2 ram work. Check joy port or Simulate press key beetwen AY and 147
Still don't understand the black screen, white text symptom.
Quote from: Rabs on 08:39, 09 March 24Still don't understand the black screen, white text symptom
look here... :-X
Quote from: Tezz on 16:13, 05 March 24Whilst I was testing however I accidentally changed my TV source to a different input and when changed back to SCART the CPC's output was in colour with the correct blue background and yellow text. Cold starting it displays with a black background with white text again until I change my TV from one source back to SCART.
Pin32 40010 join to SOUND. I hear 300Hz interrupts...
ps. The One Wire CPC oscillosphone is a little cheaper than Rigol. ;D
Quote from: Tezz on 16:13, 05 March 24CPC's output was in colour with the correct blue background and yellow text. Cold starting it displays with a black background with white text again until I change my TV from one source back to SCART.
Maybe You must unplag CPC pin7 from your cable? Or your cable has too much damping?
Quote from: Rabs on 08:30, 09 March 24Quote from: Tezz on 15:45, 08 March 24Quote from: Bryce on 14:22, 07 March 24My next check would be the 40009 ROM. Check if it has any stuck Data or Address bits.
Bryce.
OK thanks, I'll look into that. I'm missing an oscilloscope to look at the current state but I did recently buy a TL866II Plus which I've not yet used so I could remove the ROM and check that it's ok along with the 74LS logic although from what I've read testing logic with the TL866II is not conclusive as to whether it is fully operational. It would be nice to have something like SLICE to use but £450 is a bit pricey. It's a shame there's nothing like the old Fluke 9010A functionality around today. I've always taken the lamers approach removing IC's until I find the culprit.
I use a Hantek DSO5102P oscilloscope. Makes investigating a lot simpler.
See https://www.amazon.co.uk/gp/product/B00I5EWF1U/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
Thanks, that's pretty inexpensive for what looks to be a decent oscilloscope. I'll towards buying that soon.
Quote from: McArti0 on 17:29, 08 March 24When you join LS145 pin 15 to expansion port pin 1 (sound) you hear in speaker brum 50hz scan keyboard. This is check that's interrupt and soft and z80 works fine.
Oscylosphone is in CPC :-D
I've had time today to finally check that out, (I forgot about mothers day etc happening at the weekend). The test did produce the expected buzz from the interrupt so the cpc is alive. So, the next question is where should I progress from here continuing with the diagnosis ;D
When you join LS145 pin 1,2,3,4,5,6,8,9,10,11 to expansion port pin 1 (sound) you hear in speaker brum 50hz scan keyboard but lover volume then PIN15.
Maybe this is bad plug keyboard...
Next try join AY3 PIN7,8,9,10,11,12,13,14 each to each LS145 PIN1,2,3,4,5,6,8,9,10,11. This is like press keys.
AY3 Pin7 and LS145 Pin11 probably is DEL key and beep sound.
Quote from: McArti0 on 14:34, 12 March 24When you join LS145 pin 1,2,3,4,5,6,8,9,10,11 to expansion port pin 1 (sound) you hear in speaker brum 50hz scan keyboard but lover volume then PIN15.
Maybe this is bad plug keyboard...
Next try join AY3 PIN7,8,9,10,11,12,13,14 each to each LS145 PIN1,2,3,4,5,6,8,9,10,11. This is like press keys.
AY3 Pin7 and LS145 Pin11 probably is DEL key and beep sound.
Thanks, I've now tried from AY pins 7-14 to the LS145 and no response.
Be careful, the LS145 is the "source", but it's an open collector chip, so you will not measure anything without it being connected via the keyboard to the AY.
Bryce.
Quote from: Bryce on 16:19, 12 March 24Be careful, the LS145 is the "source", but it's an open collector chip, so you will not measure anything without it being connected via the keyboard to the AY.
Bryce.
Ok so a direct wire between LS145 and AY won't actually work. So, I guess I'm left with either the PIO, AY or LS145 to look into
Will I get key presses registered with a wire between the pins of LS145 and AY with the keyboard membrane connected?
Yes a wire between the pins of LS145 and AY is the same like key press.
Output LS145 "you will not measure anything" only when you measure between 0V and Pin. When you join a wire to sound line R114 you can hear 50Hz buzz in speaker.
you can check whether the AY3 inputs are high ~5v
AY3 Pin7-14 join to mass 0V should end with chars printout.
Check Output from AY3 Pin21-28 buzz 50Hz when const 0V at input Pin 7-14.
Check Buzz 50Hz at AY3 Pin18,20 control lines.
Check ~0V at ROMEN Pin20 40009
Quote from: McArti0 on 15:44, 13 March 24Yes a wire between the pins of LS145 and AY is the same like key press.
Output LS145 "you will not measure anything" only when you measure between 0V and Pin. When you join a wire to sound line R114 you can hear 50Hz buzz in speaker.
you can check whether the AY3 inputs are high ~5v
AY3 Pin7-14 join to mass 0V should end with chars printout.
Check Output from AY3 Pin21-28 buzz 50Hz when const 0V at input Pin 7-14.
Check Buzz 50Hz at AY3 Pin18,20 control lines.
Check ~0V at ROMEN Pin20 40009
Thanks for your further help,
connecting ground to AY pins 7-14 has no response with chars output.
AY inputs (pins 7-14) all show 4.46v.
AY pins 18 and 20 do produce buzz.
ROM pin 20 shows 3v.
Thanks again
Pin 20 3V ROM swithed between RAM and ROM. A little more RAM then ROM.
Check voltage at A11,A12 Pin1,2 of Z80 . it should be close to ~4.5V. Main Loop read program from 1BXX,1CXX, 1DXX (but here is I-reg too)
Check voltage at A0, Pin30 of Z80 . it should be close to ~2.5V
Quote from: McArti0 on 13:34, 14 March 24Pin 20 3V ROM swithed between RAM and ROM. A little more RAM then ROM.
Check voltage at A11,A12 Pin1,2 of Z80 . it should be close to ~4.5V. Main Loop read program from 1BXX,1CXX, 1DXX (but here is I-reg too)
Check voltage at A0, Pin30 of Z80 . it should be close to ~2.5V
Z80 pin 1 : 2.13v
Z80 pin 2 : 2.31v
Z80 pin 30 : 1.61v
(Btw I have previously tried swapping a known working Z80 with no change to the issue)
This voltages is an attempt to estimate whether the correct character reading program is being executed. Without any tools. I check this at home, but i think volt. at Pin2 is too small.
Quote from: McArti0 on 16:16, 14 March 24This voltages is an attempt to estimate whether the correct character reading program is being executed. Without any tools. I check this at home, but i think volt. at Pin2 is too small.
Thanks for looking into it, very much appreciated. Will get there in the end!
Check this scenario. Cold cpc. Press and hold DEL and turn on cpc. Are You hearing sound? 0,5 SEC? 0,2 SEC? 0,01sec? 0,00....
Quote from: Tezz on 18:04, 05 March 24I also have a working long board 464.
You can compare voltages Addresses line.
What is the current status?
Is there still the power on message on the screnn but yellow on black and then nothing happens?
That is beyond ROM not working. ROM is working otherwise you would not get there. Same is true for Ram. If you would have a defective RAM chip, you would see it in the picture.
Is the sound chip getting a clock signal at all? It is very unlikely that it would not, because the screen works and if the clock from GA would not get out, the CRTC also would not work. But no clock signal on the AY would result in no keyboard and no sound.
Measuring Voltage on Address or Datalines is not really helpful other it is maybe completely stuck.
But as we see the power on message, there is neither a problem with addressing nor with data bus. Also Ram works (read and write) so even GateArray control and the Latch and Buffer working fine.
The GateArray might be defective as it potentially cannot display blue anymore. If it can only display Read and Green you would get black background with Yellow letters.
That is what is coming to my mind.
An Oscilloscope would be very helpful to understand what is going on. Then measuring address lines or datalines in any way would be more helpful.
A12 Pin 2 i have ~2,25V its always 1 from PC and 0 from I-register. its correct.
Black screen is not true.
Quote from: Tezz on 16:13, 05 March 24however I accidentally changed my TV source to a different input and when changed back to SCART the CPC's output was in colour with the correct blue background and yellow text. Cold starting it displays with a black background with white text again until I change my TV from one source back to SCART.
Tezz did not test with a buzz speaker test Pin 21-28 of AY3 when he connects pins 7-14 to ground.
Voltage on nCPU/CLK AY3 PIN15 is ~2.5V when clock is working.
I wonder what happens to AY and PPI when AY 3 Pin 21-28 is out and PA is out for a long time.
AY has CLK because this the same as nCPU. nCPU work because Screen is visible and CPU work because scaning keyboard. BC1, BD1 (Pin18,20) has buzz on speeker.
Quote from: McArti0 on 17:06, 14 March 24Check this scenario. Cold cpc. Press and hold DEL and turn on cpc. Are You hearing sound? 0,5 SEC? 0,2 SEC? 0,01sec? 0,00....
Ok, I've tried this now. I don't hear any sound even a millisecond blip at all holding down DEL with a cold start.
I received some 4164 RAM this morning so I've swapped out the single 4264 for good measure with MT RAM well known reputation although it was tested.
To clarify, the 464 starts with the correct startup being displayed but with a black border and black background with white text and no keyboard response. If I change the TV source away from SCART and back to SCART whilst it's in this frozen state the display is then in the correct colours with blue background and yellow text, still frozen.
Keyboard has been tested on my other long board 464 and I've swapped in known working Z80 and Gate array with no change. Original Z80 and gate array are back in place.
AY3 probably died
Quote from: McArti0 on 15:44, 13 March 24Check Output from AY3 Pin21-28 buzz 50Hz when const 0V at input Pin 7-14.
There's one AY-3-8912A currently listed on eBay https://www.ebay.co.uk/itm/256299151144
AY3 Pin21-28 buzz Loud 50Hz is const at normal work. BUT when e.g. Pin 14 join to ground, buuzz at Pin28 is noticeably quieter.
Just swap the AY. They are known to fail and every other chip involved is magnitudes more reliable than it. The AY is directly connected to the Joystick port and is highly exposed to static discharge.
Bryce.
Thanks all, I've bought the replacement AY now so will swap that next once it arrives and see how it goes.
The replacement AY arrived this morning, the removal of the existing AY from the board went well so I've now installed a socket but sadly there's no change with the replacement AY. Still starting with a black background and no keyboard response. So guys what's the next move with the diagnosis? :)
Quote from: McArti0 on 21:27, 15 March 24AY3 Pin21-28 buzz Loud 50Hz is const at normal work. BUT when e.g. Pin 14 join to ground, buuzz at Pin28 is noticeably quieter.
Quote from: Tezz on 15:24, 19 March 24The replacement AY arrived this morning, the removal of the existing AY from the board went well so I've now installed a socket but sadly there's no change with the replacement AY. Still starting with a black background and no keyboard response. So guys what's the next move with the diagnosis? :)
I still don't understand the black screen and white text. Further I don't understand how it gets to a Ready prompt then freezes. What is even more confusing is the changing inputs on the monitor gets you back to a blue screen yellow text.
Going back, the CPC was fine, you then got the grey screen, typical memory failure, found a faulty RAM chip, then the black screen and white text fault appeared?
If the RAM was still faulty then surely the CPC would not get to a Ready prompt?
If the ROM was faulty would it get to a Ready prompt?
The screen output looks OK, at least after changing monitor inputs, so the CRTC and GA are working?
Now I know the AY is generally the problem with keyboard input and indeed I have fixed at least two with an AY fault but the last CPC I repaired actually had a faulty 8255 PIO.
Also what type of AY did you buy the AY-3-8912A does not have any internal pullups on the IO port.
remove AY3, turn on CPC and by resistor 22k?? Pins 21-28 join to ground. Make PA null when PA is Input. But only whithout pullup, PA should be null at all pins?
Quote from: Rabs on 19:32, 19 March 24Also what type of AY did you buy the AY-3-8912A does not have any internal pullups on the IO port.
Yes, I bought the AY3-8912A.
It was 10 years ago (not long after it was bought) when the cpc died during loading. All was fully working prior.
It's an odd one now that the identified single faulty RAM IC has been replaced that it has this behaviour.
Quote from: Tezz on 19:54, 19 March 24Quote from: Rabs on 19:32, 19 March 24Also what type of AY did you buy the AY-3-8912A does not have any internal pullups on the IO port.
Yes, I bought the AY3-8912A.
It was 10 years ago (not long after it was bought) when the cpc died during loading. All was fully working prior.
It's an odd one now that the identified single faulty RAM IC has been replaced that it has this behaviour.
See I go back to that, you replaced a RAM IC and it started this odd behavior.
Where is 8912A on your photo...
https://www.cpcwiki.eu/forum/hardware-related/cpc-464-freezes-on-start-up-with-black-background-colour/msg236668/#msg236668
Perhaps Replace the IC 125 "MT RAM" as these have been known to be not reliable
Good Luck
Keep Safe
Ray
how reset works? IC110 pin2 to ground.
Quote from: Audronic on 23:44, 19 March 24Perhaps Replace the IC 125 "MT RAM" as these have been known to be not reliable
Good Luck
Keep Safe
Ray
QuoteQuote from: Tezz on 15/03/2024, 12:21:
I received some 4164 RAM this morning so I've swapped out the single 4264 for good measure with MT RAM well known reputation although it was tested.
Quote from: McArti0 on 20:22, 19 March 24Where is 8912A on your photo...
I've now reinstalled the original AY into the socket.
Quote from: McArti0 on 08:34, 20 March 24how reset works? IC110 pin2 to ground.
It works, IC110 pin2 to ground does reset the CPC.
Thanks.
Quote from: McArti0 on 19:52, 19 March 24remove AY3, turn on CPC and by resistor 22k?? Pins 21-28 join to ground. Make PA null when PA is Input.
Quote from: McArti0 on 14:19, 20 March 24Quote from: McArti0 on 19:52, 19 March 24remove AY3, turn on CPC and by resistor 22k?? Pins 21-28 join to ground. Make PA null when PA is Input.
Thanks, I'll try that in the morning. Could you explain the expected result of the test?
Thanks again.
print chars on screen.
and you can test wired LK1 and run CPC.
You will see Orion on the screen instead of Amstrad.
This will confirm that PB in 8255 is working.
One idea may be to replace the onboard ROM with the Diagnostics ROM. This will at least test the RAM and eliminate the ROM.
Here is a pic of the Diagnostics ROM installed in my 464.
Diag ROM on board.jpg
And a pic of the screen after it tests the RAM.
screen shot.png
Next chip to desoldering. 8255 next etc. maybe something for an expansion port
Quote from: McArti0 on 07:32, 22 March 24Next chip to desoldering. 8255 next etc. maybe something for an expansion port
Why? It's the most reliable chip in the entire CPC.
Bryce.
I have an idea that 8255 was shot from the tape.
Quote from: McArti0 on 22:26, 22 March 24I have an idea that 8255 was shot from the tape.
It would be the first time that happened. It's still much more likely, that the ROM is corrupted.
Bryce.
Dandanator would come in handy
Quote from: McArti0 on 17:55, 23 March 24Dandanator would come in handy
A Dandanator within the Lower Diagnostics ROM loaded would be a good option as the Diagnostics ROM would checksum the onboard ROM as well as test the RAM.
ok how to test AY3 as gate.
pin2 LS145 permanently connected to READY Exp port pin40.
Then cpc will stop at address 08A1 (0864 for 464) and 8255 PA will be as input and AY3 as output DA, input PA.
AY3 pins 21-28 has 5V voltage. if Pin 7-14 short to ground then Pin 21-28 has 0V (Pin 14 in - Pin 28 out e.t.c.)
ps. works great!
Thanks all, my first thought was to check it out with the Dandanator. Rob has kindly offered to send a diagnostics ROM. The cheapest I can see the Dandanator mini is roughly £39 including shipping from Spain. That way I can hopefully check out the ROM Insitu along with the RAM.
It's actually £15 shipping to the UK so it works out no cheaper than the ones listed on eBay. I've not yet ordered one.
I'm just getting back onto this today, I think the first step will be desoldering the ROM and checking it out making use of the TL866II+. I have one more 28 pin socket left so I'll have the board ready for a replacement or returning the original back if all looks good there
I've eventually read the ROM using my TL866II+ and all appears to fine with it. I compared my 32kb ROM dump against the standard BASIC/OS downloaded from the wiki using binary compare via windows FC.EXE. I can upload the dump if that's allowed on the forum. So, the issue with this board lies elsewhere, perhaps still a RAM promblem?
Now you have the TL866II+ setup you could create a Lower Diagnostics ROM, to check the RAM.
Quote from: Rabs on 18:40, 03 April 24Now you have the TL866II+ setup you could create a Lower Diagnostics ROM, to check the RAM.
Definitely the next move!
I've received my EPROMs and flashed Noel's diagnostics ROM. The CPC starts with a beep, does bit pattern, double beep then the diagnostics display. There's nothing from the keyboard input although as the diagnostics is in place of the firmware in the ROM I assume the diagnostics ends once it's passed through a RAM test and of course reports unknown cpc. I'm unfamiliar with it however, I should read the sources.
what should be the next move?
Keyboard should still work and is that screen in black and white? How weird. RAM test has passed. AY sound chip is working as you heard the beep and must have been programmed via the 8255 PIO.
Ah ah you have no CRTC type being displayed.
Quote from: Rabs on 13:34, 09 April 24Keyboard should still work and is that screen in black and white? How weird. RAM test has passed. AY sound chip is working as you heard the beep and must have been programmed via the 8255 PIO.
Ah ah you have no CRTC type being displayed.
Hi, yes it does start in black and white just as the standard ROM did although again changing the TV source from and to SCART the colour output is there.
It'll certainly be interesting to finally discover what's been causing the issue!
Keyboard was tested and not work?
A clue, I think, is that the Diagnostic ROM is not reporting the CRTC type.
You should be seeing something like this. See how the CRTC type is reported as 00. I think Diagnostic ROM is just executing a simple IN against the CRTC status register and yet it is hanging, or looks like it from your screen shot.
20231022_143743~2.jpg
Looking at the Diagnostic ROM Code, it writes to Reg 12 of the CRTC before reading port B on the 8255 PIO waiting for VSYNC before then going on to read the status register and determine what type of CRTC it is. At least I think so. But VSYNC must be ok otherwise the screen would be corrupt. So is it stuck here? PIO? But at this point I am starting to guess...a lot...
GetCRTCType:
ld bc,#bc0c ; select reg 12 (R/W)
out (c),c
ld bc,#bd00+%0110100 ; write a value
out (c),c
; call wVb
ld b,#f5 ; wait Vbl
@vbLoop1
in a,(c)
rra
jr c,@vbLoop1
@vbLoop2
in a,(c)
rra
jr nc,@vbLoop2
ld b,#be ; read from status register
in a,(c)
ld d,a
Or. Something wrong was happend with CRTC, A14 or nand IC110. When reading PA F4 reading FF from CRTC too.
Quote from: Rabs on 16:28, 09 April 24A clue, I think, is that the Diagnostic ROM is not reporting the CRTC type.
You should be seeing something like this. See how the CRTC type is reported as 00. I think Diagnostic ROM is just executing a simple IN against the CRTC status register and yet it is hanging, or looks like it from your screen shot.
20231022_143743~2.jpg
Ah yes, thanks for the image, that's helpful to see that it's hung at that point. That might explain the black and white output as it hangs with the standard ROM. I'll look to replacing the CRTC next. I have some 40 pin sockets. Is there a good place to buy UM6845R?
I am not sure it is the CRTC? All it does is count VSYNC, HSYNC, Display Enable and refresh the RAM.
The registers which form the counters in the CRTC are being setup correctly, otherwise you would not have a display.
And there is not a lot between the CPU and CRTC in terms of logic.
Quote from: McArti0 on 16:13, 09 April 24Keyboard was tested and not work?
Hi, yes I tested the keyboard on my long board and all was fine there.
As @McArti0 indicated could be IC110 but equally could be IC112. If it was IC110 then I would expect the write to fail, as well as the read, and looks like that is not the case as the display is sort of working. But if IC112 failed? On a single gate, really? Guessing here without a scope. And then there is the black and white screen. What is all that about?
IORD.JPG
CRTC.JPG
No on other board but on DiagROM.
Check wire LK1, LK2 - 4. I should to change brand on screen and 50/60 Hz set. PB 8255 working or not.
Quote from: Rabs on 17:02, 09 April 24I am not sure it is the CRTC? All it does is count VSYNC, HSYNC, Display Enable and refresh the RAM.
The registers which form the counters in the CRTC are being setup correctly, otherwise you would not have a display.
And there is not a lot between the CPU and CRTC in terms of logic.
Ok, I'll take a look at the schematics for a better understanding. It would have been nice if it was down to a logic IC
Quote from: Rabs on 17:12, 09 April 24 And then there is the black and white screen.
I think its 60 Hz and bad recognize NTSC.
I have a test board with most of the BIG ICs socketed, except for IC112 and IC110 :picard: ,otherwise I could have simulated some gate failures for you to see if I get the same symptoms.
If you are still stuck by the weekend, I can do that.
Quote from: Rabs on 17:20, 09 April 24I have a test board with most of the BIG ICs socketed, except for IC112 and IC110 :picard: ,otherwise I could have simulated some gate failures for you to see if I get the same symptoms.
If you are still stuck by the weekend, I can do that.
That would've been great to know if the two ICs were socketed!
Still not sure because if the IORD was at fault, would the CPU just not read random data and not not crash or hang?
On the off chance have you got or tried a spare Z80?
Quote from: McArti0 on 17:13, 09 April 24Check wire LK1, LK2 - 4
Please check this!
LK1, LK2, LK3, LK4. or 8255 pin 19,20,21,22 to ground and turn on CPC. changing Brand on screen
Test Does this computer read any IO!!!
Quote from: Rabs on 17:52, 09 April 24On the off chance have you got or tried a spare Z80?
Yes I've swapped the Z80 previously with the known working one in the long board
Quote from: McArti0 on 17:56, 09 April 24Quote from: McArti0 on 17:13, 09 April 24Check wire LK1, LK2 - 4
Please check this!
LK1, LK2, LK3, LK4. or 8255 pin 19,20,21,22 to ground and turn on CPC. changing Brand on screen
Test Does this computer read any IO!!!
Ok, will take a look at that, thanks
Quote from: Rabs on 17:51, 09 April 24Still not sure because if the IORD was at fault, would the CPU just not read random data and not not crash or hang?
Rabs. What can be read in CPC? "Never" read CRTC, 8255 PA, 8255 PB. thats all.
PB at start and as Tape, PA as keyboard.
Actually links on PORT B of the PIO is not a bad shout. These drive the branding on the start screen and looking at earlier when you had the OS and BASIC ROM in it looked ok. So reading that ok, maybe. I am stuck at this point.
IC 112 pin6 voltage nearest 5V - sound ~50Hz.
Oh hang on
@McArti0 may be correct about the 60Hz thing.
So you don't have any link in LK4, so should be 50Hz (I think). You are using a modern TV (I assume with a SCART connection?) and you get black and white. Quick google and there is some inference that if at 60Hz you get black and white (maybe someone else can confirm this happens). What if the CRTC is a bit dodgy, somehow?
Your PCB below
LNK4.jpg
By the way I socketed IC112 and tied pin 6 high to simulate a fail on IORD and it does not give your symptoms.
Quote from: Rabs on 21:16, 09 April 24Oh hang on @McArti0 may be correct about the 60Hz thing.
So you don't have any link in LK4, so should be 50Hz (I think). You are using a modern TV (I assume with a SCART connection?) and you get black and white. Quick google and there is some inference that if at 60Hz you get black and white (maybe someone else can confirm this happens). What if the CRTC is a bit dodgy, somehow?
Your PCB below
LNK4.jpg
By the way I socketed IC112 and tied pin 6 high to simulate a fail on IORD and it does not give your symptoms.
Hi, yes I'd kept an LCD TV from the time they still included analogue connections along with digital. My other systems have various TVs and monitors. I do also still have a 100hz CRT TV in my conservatory that I use when working on repairs that I can use. The CPC is connected via a SCART which is the same one I used before the fault occurred. It works fine with the long board btw on this TV.
Good to know that you've looked into IC112. Thanks for doing that. Will eventually discover the issue by process of elimination!
If you do decide to swap the CRTC, try to get a type 0.
Type 0 (Hitachi HD6845S, UMC UM6845)
Type 1 (UMC UM6845R)
Type 2 (Motorola MC6845)
"socketed IC112 and tied pin 6 high to simulate a fail on IORD and it does not give your symptoms."Nonsens. permanet +5v on pin 6 going to crash output LS132 and never read keyboard.Two tests to true.Quote from: McArti0 on 18:22, 09 April 24
Check IC 112 pin6 voltage nearest 5V - sound ~50Hz.
Wired for ex. Lk2 and turn on cpc.Two test at 60 sec!!! Not 4 days.
Quote from: McArti0 on 06:34, 10 April 24"socketed IC112 and tied pin 6 high to simulate a fail on IORD and it does not give your symptoms."
Nonsens. permanet +5v on pin 6 going to crash output LS132 and never read keyboard.
Two tests to true.
Quote from: McArti0 on 18:22, 09 April 24
Check IC 112 pin6 voltage nearest 5V - sound ~50Hz.
Wired for ex. Lk2 and turn on cpc.
You are correct sorry, I just left pin 6 floating, not connected.
Quote from: Rabs on 06:27, 10 April 24If you do decide to swap the CRTC, try to get a type 0.
Type 0 (Hitachi HD6845S, UMC UM6845)
Type 1 (UMC UM6845R)
Type 2 (Motorola MC6845)
Thanks Rob, I was reading up about the types a few days back. I'll certainly look to get the HD6845S. I read that a lot of sellers pass off the other types listing them as HD6845S so I'll have to make sure to check with the seller. The diagnostics procedure should verify it once installed too incase it's been re-screen printed in China. I'll get the original CRTC socketed today so that's it's ready for the replacement.
But why!!! Check that IORD pin6 ic112 first and PB
Your CRTC is not detected because Soft not ending this loop:
ld b,#f5 ; wait Vbl
@vbLoop1
in a,(c)
rra
jr c,@vbLoop1
This loop is reading PB 8255 and dont read Bit 0 because all IN instruction read &FF in your CPC.
You understand?
Hi, I know what you mean, but what confuses me is that the Diag ROM is able to read the link status connected to port B.
It is even reporting the refresh of 50Hz from link 4.
IMG_20240409_125929.jpg_thumb.png
Then it hangs at the point it attempts to read the CRTC register.
And then why is it in black and white.
I must admit I am very confused.
By the way I did close link 4 on my CPC to select 60Hz and on my TV it was still in colour.
Quote from: Rabs on 22:19, 10 April 24confuses me is that the Diag ROM is able to read the link status connected to port B.
Not able to read ;D
Look. If You have bad read FF that is mean like LK1-4 Hi , Printer Busy Hi, Vsync always Hi. Tape data read Hi. Exp is Hi
All is "good"
Ok, catching up this morning. This would suggest either the PIO or IC112 (SN74LS32N).
Could you explain clearer the test needed at pin 6 of IC112.
I could remove it and test in the TL866II+ if necessary. They're only 50p or so if it needs to be replaced
Pin6. Check by multimeter - voltage ~4,9V
Pin6 wired to sound line pin1 expansion port. Hear sound 50hz. If ic112 is seek then no sound.
Second. Lk2 wired and turn on cpc. On screen should be brand Orion not Amstrad
How sound work You can test on pin3 ic112 IOWR because work good.
Quote from: McArti0 on 13:05, 11 April 24Pin6. Check by multimeter - voltage ~4,9V
Pin6 wired to sound line pin1 expansion port. Hear sound 50hz. If ic112 is seek then no sound.
Thanks! I'll do those tests this afternoon.
Ok, voltage at pin 6 of IC112 is 3.91v. pin 6 of IC112 to expansion port pin one produces a quiet buzz with line noise (This is with the diagnostics ROM installed). shorting LK2 with a wire link, diagnostics ROM still reports Amstrad.
do You check pin3 to compare.? This is LOUD Buzz.
Quote from: Tezz on 14:39, 11 April 24shorting LK2 with a wire link, diagnostics ROM still reports Amstrad.
Crash ic112. Insert original Rom and repeat test.
I've retested with the standard ROM installed, IC112 pin 6 voltage is 3.8v, pin 6 of IC112 to expansion pin 1 gives the same output as previously with the diagnostics ROM installed, a quiet line noise. Pin 3 of IC112 to expansion pin 1 produces clear loud buzz. Shorting LK2 still shows Amstrad.
Last test ic112 before desolder.
Pin 37 expansion port BUSRQ to ground, pin 4,5 ic112 to ground and You should have 0V on Pin6 but you have not.
Pin 37 expansion port BUSRQ to ground, pin 1,2 ic112 to ground and You should have 0V on Pin3 and you have.
Quote from: McArti0 on 16:36, 11 April 24Last test ic112 before desolder.
Pin 37 expansion port BUSRQ to ground, pin 4,5 ic112 to ground and You should have 0V on Pin6 but you have not.
Pin 37 expansion port BUSRQ to ground, pin 1,2 ic112 to ground and You should have 0V on Pin3 and you have.
Ok, thanks. I'll try that too.
These SN74LS32 are listed on eBay, 10 for just over a fiver. Photo seems to show the correct SN74LS32N but can you confirm these are correct for me to order.
https://www.ebay.co.uk/itm/166211136961
Thanks again to all!
YES ok
I've now removed IC112 from the board and installed a socket. The new SN74LS32N are on the way.
I wanted to test this logic IC in my TL866II but the latest version of xgpro seems to have removed all the 74 logic from the list. Is there something I'm missing with this latest version in order to test it?
Select Tools then Logic Test and 7432 but this is with version 11.9
7432.JPG
Quote from: Rabs on 14:50, 12 April 24Select Tools then Logic Test and 7432 but this is with version 11.9
7432.JPG
Ah, thanks for the info, I did see 7432 listed but wasn't entirely sure it was actually 74LS32 as they were specifically listed in previous versions
Test seems to pass with the same result as your screenshot
Mayby not work on hi freq. Try now connect 4,5 pin to z80 pin 20,21.
The 7432s arrived this morning but no change with the new one installed unfortunately.
Quote from: McArti0 on 16:36, 11 April 24Last test ic112 before desolder.
Pin 37 expansion port BUSRQ to ground, pin 4,5 ic112 to ground and You should have 0V on Pin6 but you have not.
Pin 37 expansion port BUSRQ to ground, pin 1,2 ic112 to ground and You should have 0V on Pin3 and you have.
You can instead search for busrq Just take out the Z80.
Quote from: McArti0 on 12:00, 15 April 24Quote from: McArti0 on 16:36, 11 April 24Last test ic112 before desolder.
Pin 37 expansion port BUSRQ to ground, pin 4,5 ic112 to ground and You should have 0V on Pin6 but you have not.
Pin 37 expansion port BUSRQ to ground, pin 1,2 ic112 to ground and You should have 0V on Pin3 and you have.
You can instead search for busrq Just take out the Z80.
Ok, will check this out next, thanks.
Quote from: McArti0 on 16:36, 11 April 24Last test ic112 before desolder.
Pin 37 expansion port BUSRQ to ground, pin 4,5 ic112 to ground and You should have 0V on Pin6 but you have not.
Pin 37 expansion port BUSRQ to ground, pin 1,2 ic112 to ground and You should have 0V on Pin3 and you have.
Ok made some time today to do this...
Pin 37 expansion to ground, pin 4&5 of IC112 to ground, pin 6 reads 0v
Pin 37 expansion to ground, pin 1&2 of IC112 to ground, pin 3 reads 3.6v
Quote from: Tezz on 18:52, 16 April 24Pin 37 expansion to ground, pin 1&2 of IC112 to ground, pin 3 reads 3.6v
this is proof that ic112 has a defect. but the computer shows that this track is working properly, so you probably shorted pins 1,2 to ground incorrectly.
Quote from: McArti0 on 19:03, 16 April 24Quote from: Tezz on 18:52, 16 April 24Pin 37 expansion to ground, pin 1&2 of IC112 to ground, pin 3 reads 3.6v
this is proof that ic112 has a defect. but the computer shows that this track is working properly, so you probably shorted pins 1,2 to ground incorrectly.
Hi, I double checked that pins 1&2 were shorted to ground. I used one wire across pins 1&2 to ground
Ok. Now Insert ROM diag, and when CPC freeze You connect new Diode, catode to Pin 6 ic112, anode to Z80 WAIT line (or READY on exp port) this connect must be strong and const.
This halted Code on Read 8255 PB instruction. You can check input voltage on D0-D7 line. D0 should be 0 , D1-7 ~5V.
But have You diode?
0+0=0 you cant have 3,6V on Pn3
I have some 1N4148 diodes
Quote from: McArti0 on 19:48, 16 April 240+0=0 you cant have 3,6V on Pn3
I'll repeat the test again in the morning
test input 8255
Quote from: McArti0 on 22:08, 18 April 24test input 8255
Thanks, I will certainly do this.
I didn't get free time yesterday to progress with testing but I intend to look more into the PIO.