Schneider CPC464 white rectangle no boot

[Flywheel]

Hi,
I have this CPC464 that worked fine, but suddenly stopped booting.
When I switch on the system, it displays a white rectangle (black border) and nothing else.
Can anyone give me some clues what I can test to fix this problem?
My best guess is some RAM has failed, but I'm not sure. They don't get warm and the 5V is okay.

[abalore]

Yes, the best guess is the RAM. The white rectangle means the screen geometry is being set, that requires the CPU, CRTC, GA and ROM to be working.

[McArti0]

If you don't know digital electronics, take it to a repair shop. If you have a workshop and electronics are familiar to you, we can guide you.

[eto]

Hi,
I have this CPC464 that worked fine, but suddenly stopped booting.
When I switch on the system, it displays a white rectangle (black border) and nothing else.
Can anyone give me some clues what I can test to fix this problem?
My best guess is some RAM has failed, but I'm not sure. They don't get warm and the 5V is okay.

Did you use a different power supply?


As others already mentioned it is most likely the RAM or one of the ICs related to RAM.

If you have a Lower ROM board (or M4 or Dandanator) you can run the Amstrad diagnostics ROM.

[Flywheel]

To answer some of the questions:

- I have experience enough with electronics, but not with the CPC464 specifically. I could desolder the RAM chips and socket them, but it is a lot of work as they are not socketed yet.
- I used a switched 5V power supply, I have only used that one so far. That adapter has been tested and works fine.
- I don't know what is a Lower ROM board, M4 or Dandator. The board is an orginal long board (I've seen pictures of smaller boards,this board is larger size), nothing has been modded, it looks spotless and as I said it worked fine but suddenly broke down after some tests with the casette deck. I switched it off and when switching back on it didn't work anymore. The cassette system seems to work fine.

Question: is there any other IC that could be faulty, or is my only option to have to remove/replace all the RAM chips one by one?

Thanks for all your help!

[Audronic]

Hi Flywheel

Where are you located ?
There may be somebody local that can help

[McArti0]

You can do the test
1 enable cpc.
2 put +5v on the RAMDIS line and keep.
3 put +5V on the ROMDIS line and keep.
4 on output RAM pin 14 all of IC RAM should be number 39h. Hi is around 2V.
This means that the RAM is probably alive.

[eto]

- I have experience enough with electronics, but not with the CPC464 specifically. I could desolder the RAM chips and socket them, but it is a lot of work as they are not socketed yet.

True, it's some work. When you do it be careful to not rip off solder pads or destroy traces. (If it happens you usually can repair it with some additional wires, so no worries if it happens.)

I don't know what is a Lower ROM board, M4 or Dandator.

They basically provide an external ROM which takes over control of the CPC. The Amstrad diagnostics ROM checks the internal RAM and on screen gives a visual of which bit of RAM is failing. 

Question: is there any other IC that could be faulty, or is my only option to have to remove/replace all the RAM chips one by one?

Yes. Any IC that is related to the RAM circuit could be the culprit. There are also some multiplexers and a latch which could cause this. However, at least from what I read so far here and on other boards, they are less likely to fail, at least if there was no overvoltage.

This video perfectly explains what is going wrong when RAM is malfunctioning on. a CPC: https://www.youtube.com/watch?v=BLzHPf1IY8c&list=PLmbYPqkyiASzW4qc1NOZCIBwb82tjtz_e&index=14

I recommend to watch the whole video as it will help you understand how things work together and how it can be repaired. There are even more really helpful repair videos on his channel (check out the Amstrad CPC playlist).