Odd text issue with cpc464

[Nanoshock]

Hi all, having a bit of a weird one with a recent purchase of a cpc464 with ctm644 monitor.


Boots fine to blue screen and white text, but within a second of booting, under them"Ready" text,   963RUN" appears followed by a combination of error messages and random special characters.
I figured it might be the AY-3-8912 so I pulled it and socketed a matching chip (not an A or /P variant) and it displays the exact same issue as before.
However with the AY left off the board it skips the 963RUN" and just progressively fills the screen with special characters instead.


The other off one is that when the screen first turns on its sstable and fine, but as soon as text begins to appear (AY installed OR removed) the whole screen begins to roll as if you had adjusted vhold dial on the monitor.


All of this happens with or without the keyboard connected, and with keyboard connected, holding down delete or any other button does nothing.


Board is a MC0044D E


Any ideas what the culprit could be?

[Bryce]

I assume you've checked the voltages? Next step would be to swap the CPU to check that it's not the issue (and because it's easy due to being socketed). Once you've elliminated that, the most likely culprit would be a dodgy lower ROM.

Bryce.

[Nanoshock]

Thanks, I've ordered a new cpu to test with, if that doesn't fix it I'll try the lower rom, I assume this would need to be programmed ? If so where would be the best source for one without buying or building a programmer?

[Bryce]

I can organise a programmed EPROM for you if you need one. Just send me a PM when you get that far.

Bryce.