Garbled screen

[crlarsen]

I haven't repaired a lot of Amstrad, but I just got my hands on a machine, which produces the below garbled output. Has anyone got suggestions on how to fix it?

[McArti0]

What amstrad?

Try ROMDIS to +5v

[crlarsen]

Hi, I have gotten a bit further, as I was able to program an EPROM with Noel's diagnostics on it. Trouble is that the results are inconsistent. It fails very time on the RAM check, but it doesn't consistently report he same bits as faulty. I have desoldered the ICs taking care o bits 0 and 1 and tested them outside the board. Both were fine.

[crlarsen]

Also to your question: A CPC464 

[eto]

Hi, I have gotten a bit further, as I was able to program an EPROM with Noel's diagnostics on it. Trouble is that the results are inconsistent. It fails very time on the RAM check, but it doesn't consistently report he same bits as faulty. I have desoldered the ICs taking care o bits 0 and 1 and tested them outside the board. Both were fine.

Did you use Amsdiag instead of the internal ROM or with an external ROM board?

Are the reported bits totally random and every bit is affected or only a few of them? if the latter: which ones? Only 0 and 1?

[crlarsen]

I have programmed an EPROM and installed it instead of the internal ROM. 

As for the results, I recorded a run where it repeated the RAM test multiple times.

Bad bits:
Run #1: 1, 4, 6, 7
Run #2: 1, 4, 7
Run #3: All bits

I have desoldered IC119 and IC120 and both testet OK in a chiptester, which usually is reliable 

[crlarsen]

I have desoldered RAM bit 4, 6 and 7 now and all test good in my chip tester.

[eto]

Could be IC114 (74LS373).

Btw: Did you already check the voltage inside the 464? Is the voltage on the ICs close to 5V?