In for repair was a clean Cave Guwange board with faulty graphics.
These boards use a powerful sprite engine consisting of four SMD ROM chips feeding into a large custom chip labeled 013. The rendered sprite data passes from 013 into two 512kb SRAM chips functioning as a frame buffer – the two SRAM chips alternate per frame. The board also incorporates three separate background tiling engines, each consisting of a ROM and a custom chip labeled 038. The backgrounds render directly to the display without a frame buffer.
I decided to tackle the sprite corruption first. These boards make heavy use of surface-mounted components, and pressing on the board near the center with a pencil eraser caused the sprite garbage to change – a sign that some of the surface-mounted chip legs were loose on the board.
Reflowing the solder on the 013 sprite custom improved things a bit.
And then reflowing the solder on both the Sprite ROMs and frame buffer RAM chips fixed the sprites completely.
One of the background layers was still showing addressing issues in the Character Select screen though. And the background would still flicker when pressing around the board with the pencil eraser, so there were still more loose part legs.
Reflowing all three of the ROM chips used for the three background processors resolved the background problems, and the board was looking really good at this point.
However, there was still one glitch that concerned me. After inserting a credit and pressing Start, there is a quick transition from the title screen to the Character Select screen. And that transition looked like graphical garbage.
However, I couldn’t find any other obvious issues with the board itself, and playing through the game the entire game didn’t reveal any other problems. I checked some YouTube playthroughs of the arcade game that showed the same corruption on the transition effect, and another repair tech confirmed it by sending me a short video of his board exhibiting it as well. The game is *supposed* to transition this way!
That wraps up this Guwange board repair. One of these days, I’ll take another look at my own personal Guwange board which has problems that look much more severe than this one.
