Hi
I bought myself another 464 last week after being without one for a few years. Its great to be back on the forum and back as a proud owner of a 464 again :D
It was sold as untested but did state that it powered on.
I opened it up and stripped it down when it arrived and gave it a good clean with a soft brush for the dust and isopropyl and a soft toothbrush for the board and all the connectors etc.
I bought a power supply and scart adapter lead from cool novelties.
It powers up fine with a nice strong red led, the fast forward and rewind work fine on the tape deck but I am getting no display output at all on the tv (same tv I used with my previous 464 a number of years ago). I put the volume right up on the 464 and pressed DEL but Im getting no beeps at all although at full volume Im hearing quite a bit of crackle through but Im not sure if this is normal or not.
Any ideas as to what to do to narrow down the fault? I have a multimeter and some basic soldering skills. Would love to get this 464 up and running again, my 9 year old son was so disappointed when it didn't work!
If its beyond my capabilities to troubleshoot and repair I may have to send it to Bryce if he's still providing this service.
no signal at all or is there at least a gray rectangle on screen?
No signal at all unfortunately :(
Quote from: Cribbyrhymes on 14:18, 06 September 23No signal at all unfortunately :(
Black Screen could be a number of things unfortunately. Where are you based?
Im in Northern Ireland
Quote from: Cribbyrhymes on 16:51, 06 September 23Im in Northern Ireland
Ah shame, bit bit far to help.
Do you have a multimeter?
It is worth to check if you have power at all (does the power LED light up?).
And then start measuring if the chips get power. Just a first indicator of broken solder joints or even short circuits.
If you do not measure any voltage between +5V and GND, you have either a dead power supply, or a short somewhere.
Yes I have a multimeter.
The machine powers up ok, power led is on and tape deck rewinds and fastforwards but no display.
Im new to testing voltages so bear with me, I take it Im testing the +5v and ground pins on each chip? Im assuming there are pin out schematics on the wiki here?
Thanks for all the replies so far
Quote from: Cribbyrhymes on 18:39, 06 September 23Im new to testing voltages so bear with me, I take it Im testing the +5v and ground pins on each chip? Im assuming there are pin out schematics on the wiki here?
Schematics:
https://www.cpcwiki.eu/index.php/Schematics
Thank you, I'll do some testing tonight with the multimeter and report back
If you press the "DEL" key, do you get a beep (turn up the speaker).
This will verify if your CPC actually works, and you just do not have any screen, or if it does not work at all (e.g. CPU not processing correctly).
It can be still a lot of things.
GateArray is the obvious candidate. If that is dead, you will have no output at all as it creates the RGB signals and the SYNC signals.
One last question:
It looks like you are using a "TV".
Did you CPC come with the normal Green Monitor or Color Monitor?
I am just asking, because if you connect it to a modern digital monitor, there might be some other reasons why you have a black screen and nothing is wrong with the CPC.
Quote from: SerErris on 22:31, 06 September 23GateArray is the obvious candidate. If that is dead, you will have no output at all as it creates the RGB signals and the SYNC signals.
I had CPCs with fried RAM and ROM ICs with exactly the same effect. If e.g. a dataline is always low, it will not work at all.
Quote from: SerErris on 22:31, 06 September 23If you press the "DEL" key, do you get a beep (turn up the speaker).
He tested that already. See first message.
OK so checked some voltages with the multimeter tonight and I'm getting a solid 5v across all of the following:
IC116 40010 gate array
IC117-IC124 ram
IC111 Z80 (although its the only chip on the board that is getting hot)
IC103
IC108
IC102
IC107
Are there any others I should be checking? My initial thoughts are the Z80 is the culprit or am I on the wrong path?
Thanks for all the replies so far
Quote from: Cribbyrhymes on 09:47, 06 September 23Im hearing quite a bit of crackle through but Im not sure if this is normal or not.
This may mean that the Z80 is working.
Do you have a frequency meter?
The multimeter is a bit too small as a diagnostic tool.
I dont have a frequency meter unfortunately just the multimeter :(
A digital probe also may work. You can check the address lines if you can see them going up and down (actually working) and the datalines. For instance if you would see a data line allways high or allways low - that is a fault somewhere in the path to RAM/ROM.
But really, without OSC or other equipement you are more or less without clue what is going on.
Z80 M1 PIN27 the meter will treat it as PWM. It should be around 1.5-2V (0V or 5V is bad)
So with the multimeter on pin 27 M1 and pin 29 GND I'm getting a reading of 4.87v
IC112 74LS32 PIN8 ?
CRTC PIN 21 ?
CRTC PIN 21 - 1.52V
On IC112 is pin 1 GND?
GA work...
No 74LS32 has GND on PIN7
Thanks
IC112 Pin 8 is reading 5.03v
Z80 does not read anything from RAM and does not download instructions (M1 should often be 0V).
Also check PIN21 CPU. It should be much lower than 5V but probably won't be.
Does your ROM have socket?
Pin 21 CPU is reading 0.02v
My gate array and CPU are socketed, nothing else
Quote from: McArti0 on 11:55, 07 September 23Z80 does not read anything from RAM and does not download instructions (M1 should often be 0V).
Also check PIN21 CPU. It should be much lower than 5V but probably won't be.
Looks really like CPU does not get anything useable .... most likely running NOPs?
Can you check PIN 20 on the ROM ? That should be ROM_EN coming from the GateArray. If that is 5V it is always disabled. And all datalines will be 0 all the time if the CPU tries to read from ROM.
Same for PIN 22 on the ROM. That also should be 0V. If it is 5V, ROM is disabled and will not work.
GND on ROM is PIN 14
Working with a multimeter, I find it best to have ground connected to a stable ground (not to a pin on any chip), and then connect just the other probe to any pin you want to measure.
CPU frozen in read state ...
You would have to remove it, give power and clock and check the M1 and the others again.
many signals are open collector or open drain. Sometimes you need to check if there is a low state by checking the 5V between PIN and VCC, not GND
Quote from: SerErris on 13:21, 07 September 23Quote from: McArti0 on 11:55, 07 September 23Z80 does not read anything from RAM and does not download instructions (M1 should often be 0V).
Also check PIN21 CPU. It should be much lower than 5V but probably won't be.
Looks really like CPU does not get anything useable .... most likely running NOPs?
Can you check PIN 20 on the ROM ? That should be ROM_EN coming from the GateArray. If that is 5V it is always disabled. And all datalines will be 0 all the time if the CPU tries to read from ROM.
Same for PIN 22 on the ROM. That also should be 0V. If it is 5V, ROM is disabled and will not work.
GND on ROM is PIN 14
Working with a multimeter, I find it best to have ground connected to a stable ground (not to a pin on any chip), and then connect just the other probe to any pin you want to measure.
PIN 20 and 22 on the ROM are both reading 0V
Quote from: McArti0 on 13:22, 07 September 23CPU frozen in read state ...
You would have to remove it, give power and clock and check the M1 and the others again.
Ive taken out, reseated the CPU and turned it back on.
What do you mean by give clock? sorry I appreciate the help but I'm new to board diagnostics and repair
You must first answer the question do you want to be a service for him from start to finish? Do you want to learn everything you need and have the satisfaction of fixing it no matter how long it takes? Or would you rather give it to someone for repair?
I definitely would like to learn and have the satisfaction of fixing it. Sending it away for repair would be a last resort but if I have to do it I will. I used to repair mobile phones as a second job but it was all just part swapping no board level diagnostic and repair. Ive a growing collection of old consoles/computers and handhelds so learning this stuff and then having the skill to carry out the repair will be invaluable in the years to come.
I really do appreciate all the continued help trying to get this 464 up and running again.
http://z80.info/zip/z80cpu_um.pdf Pages 5-11 (19-25 pdf) Figure 3-7
You must to understand how z80 read instruction from memory. (for ex. why we check M1 line).
https://www.cpcwiki.eu/imgs/6/6d/Schaltplan_cpc_464.jpg
https://bread80.com/2021/06/03/understanding-the-amstrad-cpc-video-ram-and-gate-array-subsystem/
you should buy a logic analyzer (https://www.mouser.ie/ProductDetail/Red-Pitaya/25?qs=iS7aw2r6gplpQX63EeZ1Ig%3D%3D)
Quote from: Cribbyrhymes on 15:30, 07 September 23I definitely would like to learn and have the satisfaction of fixing it. Sending it away for repair would be a last resort but if I have to do it I will. I used to repair mobile phones as a second job but it was all just part swapping no board level diagnostic and repair. Ive a growing collection of old consoles/computers and handhelds so learning this stuff and then having the skill to carry out the repair will be invaluable in the years to come.
I really do appreciate all the continued help trying to get this 464 up and running again.
If you have not seen Noel's Retro Lab can I suggest you watch the videos, for example Amstrad CPC 6128 with Black Screen (https://youtu.be/EyT7gYs--vo?si=SG7LhE_6bmsRN3Hc). This is where I started and found them very helpful. Noel takes you through the basics of fault finding.
Quote from: McArti0 on 16:35, 07 September 23http://z80.info/zip/z80cpu_um.pdf Pages 5-11 (19-25 pdf) Figure 3-7
You must to understand how z80 read instruction from memory. (for ex. why we check M1 line).
https://www.cpcwiki.eu/imgs/6/6d/Schaltplan_cpc_464.jpg
https://bread80.com/2021/06/03/understanding-the-amstrad-cpc-video-ram-and-gate-array-subsystem/
you should buy a logic analyzer (https://www.mouser.ie/ProductDetail/Red-Pitaya/25?qs=iS7aw2r6gplpQX63EeZ1Ig%3D%3D)
Thank you I've a lot of reading and studying ahead of me!
Quote from: Rabs on 16:40, 07 September 23Quote from: Cribbyrhymes on 15:30, 07 September 23I definitely would like to learn and have the satisfaction of fixing it. Sending it away for repair would be a last resort but if I have to do it I will. I used to repair mobile phones as a second job but it was all just part swapping no board level diagnostic and repair. Ive a growing collection of old consoles/computers and handhelds so learning this stuff and then having the skill to carry out the repair will be invaluable in the years to come.
I really do appreciate all the continued help trying to get this 464 up and running again.
If you have not seen Noel's Retro Lab can I suggest you watch the videos, for example Amstrad CPC 6128 with Black Screen (https://youtu.be/EyT7gYs--vo?si=SG7LhE_6bmsRN3Hc). This is where I started and found them very helpful. Noel takes you through the basics of fault finding.
Thank you for the recommendation. I will watch the one you linked above tonight. Hopefully there are a few more simple things I can check to try and narrow down the issue. Looks like I might need a logic analyzer or oscilloscope to diagnose further though by the looks of things :(
OK so a change of immediate plans. I've started reading and went down a complete rabbit hole with noels retrolab videos, enjoying them a lot and learning a lot.
Its a steep learning curve though which will take time and I do have to consider spending some money on equipment down the road to compliment my multimeter.
My son though is pestering me to get this 464 up and running ASAP so I think I will send it away for repair this time if its not too expensive in the hope that in the future if it fails again I'll have better knowledge and equipment to hopefully fix it a home.
So my question is are there any recommendations for any UK based repairers? I found a few through google but any personal recommendations would be appreciated. Happy to pay for a repair but not looking to break the bank.
Thanks
I cannot do any recommendation - to be honest as I am not in UK.
However most likely you will need to pay for the hour as no one can tell you at this point in time how much efford it will be to get it back up and running (any fried chips to replace, diagnosis etc.).
To be able to really diagnose it you would need the following:
1. Oscilloscope
2. Diagnostic ROM from Noels Retro Lab
3. Seomthing to put the ROM on (like my very basic hardware to run it)
4. An EPROM with 32k
5. An EPROM Programmer
6. Optional: (multichannel) Logic Probe is helpful, but Oscilloscope is obviously better.
7. Optional: Bench Power
8. Soldering Ion
9. Optional: Desolerding Gun, or any other method to desolder chips.
If you would have the Diagnostic ROM and any form to run it, you could remove the RAM and the ROM in the first place and see if you then can see anything. It would be esp good to run it from the expansion port, as the ROM socket also can have issues.
For your analysis:
Okay ROM does get both enable singales right, so it should be active and output data.
Now you would really need a logic probe, to see if any of the data lines are continously low or high or even floating. Maybe the ROM is fried.
You may want to test the datalines of the ROM against GND to see if they are fixed, or varying. However that is very hard to do with a Multimeter, as it could not identify floating lines.
@Cribbyrhymes As a Staring piece of Diagnostic hardware Just a Logic Probe
These are less than $10.00 Australian .
PS:_ Don't purchase the Cheapest but get a Medium price one.
These can be used to show "ACTIVITY" on various pins which will indicate the state of the Pins
Good luck
Stay With the Project you will learn a LOT
Keep Safe
Ray
Quote from: SerErris on 23:09, 09 September 23I cannot do any recommendation - to be honest as I am not in UK.
However most likely you will need to pay for the hour as no one can tell you at this point in time how much efford it will be to get it back up and running (any fried chips to replace, diagnosis etc.).
To be able to really diagnose it you would need the following:
1. Oscilloscope
2. Diagnostic ROM from Noels Retro Lab
3. Seomthing to put the ROM on (like my very basic hardware to run it)
4. An EPROM with 32k
5. An EPROM Programmer
6. Optional: (multichannel) Logic Probe is helpful, but Oscilloscope is obviously better.
7. Optional: Bench Power
8. Soldering Ion
9. Optional: Desolerding Gun, or any other method to desolder chips.
If you would have the Diagnostic ROM and any form to run it, you could remove the RAM and the ROM in the first place and see if you then can see anything. It would be esp good to run it from the expansion port, as the ROM socket also can have issues.
For your analysis:
Okay ROM does get both enable singales right, so it should be active and output data.
Now you would really need a logic probe, to see if any of the data lines are continously low or high or even floating. Maybe the ROM is fried.
You may want to test the datalines of the ROM against GND to see if they are fixed, or varying. However that is very hard to do with a Multimeter, as it could not identify floating lines.
Thank you for taking the time to respond and provide so much useful information.
I really appreciate it.
I've a lot to learn and a lot of equipment to buy but who doesn't love buying new toys :)
Quote from: Audronic on 00:20, 10 September 23@Cribbyrhymes
As a Staring piece of Diagnostic hardware Just a Logic Probe
These are less than $10.00 Australian .
PS:_ Don't purchase the Cheapest but get a Medium price one.
These can be used to show "ACTIVITY" on various pins which will indicate the state of the Pins
Good luck
Stay With the Project you will learn a LOT
Keep Safe
Ray
Thanks Ray, your time is Much appreciated as is the time of everyone who has responded so far.
I will definitely pick up a logic probe to start with.
Its a steep learning curve but with time and determination I'll get there!
Thanks to all who responded, I appreciate it.
I found a UK repairer who has a good reputation and is reasonably priced so I've sent it away to him to diagnose and potentially repair it depending what the issue is.
I have a logic probe on the way and once I've done a lot more reading and bought some more equipment I'll definitely purchase another cheap faulty CPC to work on at my leisure and hopefully repair. This current one I'll keep as my main machine.
I'll update the post once I have heard back from the repairer as to what the fault was.