Status: Successfully repaired on January 10, 2024
In for repair was a Capcom CPS3 board with original SIMMs and the Darksoft UltraBIOS cart that removes the need for a suicide battery in the cartridge.
The board exhibited graphical glitching.
The onboard diagnostics flagged the Sprite RAM as the culprit.
Note that it’s normal for SIMM 1 & 2 to report NG when using the Darksoft BIOS and CD image. The game code is stored on those SIMMs and the code is modified to run without the factory encryption, thus changing the checksums that the diagnostics expect.
With every CPS3 board I work on, I open the plastic capsule to see if there is a leaky battery inside. Fortunately this board is one of the later revisions without that battery.
The Sprite RAM is located at position 1D on CPS3 and is driven by a large custom PPU chip nearby. This board also had an aftermarket heatsink attached to the PPU – a good idea since the PPU typically gets quite hot.
I carefully removed the heatsink from the PPU custom chip with a spudger.
Then I examined the Sprite RAM and PPU chip legs under a microscope. I soon noticed a spot on the corner of the PPU where two legs were bent such that they were touching together.
I used a sewing needle to straighten the bent pins out.
That fixed the board – the diagnostics now pass for the Sprite RAM and the graphics are rendering properly. Success!