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CPC464 - RAM problem of faulty SCART cable?

Started by nardj, 08:29, 26 April 23

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I just bought an Amstrad CPC464 on ebay marked untested. I quickly made a scart cable:

After connecting to my flat panel tv, I got a checkboard like image. I replaced all RAM chips with sockets and 4864-3 chips except one which is an old 4864-2 chip from the amstrad.

After this I got the following image on tv:

Any idea how to troubleshoot or maybe even what the problem seems to be?
Appreciate all the help!


press DEL. If no beep is heard. system failure. Not only screen.
CPC 6128, Whole 6128 and Only 6128, with ........
TYPICAL :) TV Funai 22FL532/10 with VGA-RGB-in.


RAM. No matter how bad the SCART cable was, it couldn't cause that screen.



Is there any way to determine which ram chip is/are the one(s)?


Yes, but you'll need test equipment or further hardware to determine this. Sometimes the faulty RAM will get hot, so you know without any additional equipment, but that's not always the case. Either way, 8x RAM plus sockets isn't going to break the bank, so it's usually faster and cheaper to just swap them all.



I removed all 8 old ram chips, put sockets in place. Since I had 7 4864-3 at hand, I swapped those out. If I read correctly they are interchangeable. 
I tried all old 4846-2 as replacement for the 8th socket, however nothing worked. Maybe one of the 4864-3 is faulty. None of them got hot.
I will order 8 new ones and hope this solves it. Thx!


I would suspect that the RAM may be too slow.
The 4864-3 RAM is 300 ns which is too slow for 4MHz system, hence why the original was 4864-2 which is 200 ns.
At 4 MHz the clock cycle is 250 ns thus 300 ns RAM is likely not going to work.
When the RAM is not working the ROM will partially work, but eventually fails as it needs RAM to work correctly and so the ROM code goes awry.

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