SRAM help

[Rossyra]

I have a CPS-1 board that appears to have a faulty SRAM chip at 1C (one of the I/O lines is completely dead, I have black bars on alternate columns on screen, plus some other corruption)

The part number is MB81C78A-45P-SK (Fujitsu sh*t chip)

I believe it's a 64K 28-pin DIP. Can anyone point me in the direction of a compatible replacement, please? Only one on eBay with the same part number is £19

 

[cliff_poole]

I looked at my CPS1 boards but I think yours must be a later one than any of mine, there were a few different versions.
For that reason, I can't be 100% sure, but I think that chip is a straight 6264 type, there should be many equivalents.

 

[Rossyra]

Thanks. I'm gonna have to dig deeper anyway. There are two of those chips together that appear to only be palette RAM, so I doubt that's causing the black bars and corruption. The fault varies from game to game, if I put G'NG on it has sprites that lag or jitter.

 

[cliff_poole]

Try putting it in to test mode using the dip switches. The test mode on some games is better than on others.
The words lag and jitter do make it sound like a RAM problem, I would guess somewhere in the big group of graphics RAM.