Need Help with 4 slot color ram

[Asi]

I've a 4 slot MVS with random bank0 color ram errors @ 400000 and snow on the screen. The Pro-B0 looks iffy -- very slight ruptures on the surface. I assume the frame buffer is bad.

Before I desolder this, could somebody provide information on the memory map / RAM addressing? ie, which chips have which address? I don't have any schematics and was concerned the problem might be in the external rams.

Thanks, Asi.

 

[Asi]

Actually, might this be one of the 64 kilobit CXK5864's?

I was reading over the MAME code and it seems there are two palette banks, 8k in size, one is at 400000h There just happen to be two 8k sony CXK5864's below the Pro-B0. So might one of these also be the cause of the errors? Anyone know about this?

I'm going to try changing these before going through the potential problems with removing and replacing the Pro-B0.

 

[Nightmare Tony]

The two 5864 RAMs form the 16 bit pallette RAM.

Asi: I've seen the tiny ruptures before; its most definitely your B0 chip gone bad.

As a point of interest, the palletes work like this:

1. The line sprite object is actually only 16 colors. This is provided by the 4 bit data. The 256 RAM used by the A0 will run a 256 pallete set, allowing for the 4096 color base sprite. The final output pallete is output through B0 to the color RAM for the 32,768 colors by another pallette added. Sort of hazy, but the double pallete system sticks out in my mind

 

[Asi]

Thank You, Tony! I appreciate your help, and I'm glad there is someone like you around.

That's also some interesting information about the palette processing.