CPC 464 start screen failure

[DFender]

I'm refurbishing an old CPC 464. It seems to work but the startup screen looks anything but ok. What would be the likely cause of this? Failing Gate Array? Perhaps some oxidizing in its connections?

[DFender]

Just found a good answer from another thread:

Look at this page of how video subsystem works:

http://bread80.com/2021/06/03/understanding-the-amstrad-cpc-video-ram-and-gate-array-subsystem/



And you have the candidate ic  list.

I first try the 74ls153. The multiplexer group that select between z80 and crtc.  As it appears that the gate array is writing things that don't should be there(wrong address?).

Al thought you can start a game first that not use  firmware calls to ensure always happend.