Feb 172019
 

Got from Portugal this Crude Buster PCB (also known as Two Crude outside Japan), an unusual and underrated beat ’em up developed and published by Data East in 1991:

Board simply booted to a white static screen:

Blank screen on boot.

The first thing I did was to check the main CPU (a custom 68000 marked ’59’) circuit and I found that both WORK RAMs (two 8K x 8-bit devices) has stuck data lines whereas address was correctly toggling :

The two RAMs are Toshiba TMM2063, we all know they are very prone to failure:

TMM2063 WORK RAMs

When I piggybacked them and got some errors (related to code execution) on screen:

Hence I decided to remove the chips:

WORK RAMs removed

Although RAMs were both tested fine in my programmer I replaced them and I got the board booting. Game was fully playable but some sound samples were wrong:

Samples are stored in two 1Mbit EPROMs and played by two OKI MSM6295 PCM chips:

Sound circuit overview

The two EPROMs were dumped as good so I fired up my audio probe and started to “listen” to output (pin 36) of the internal DAC of both MSM6295.The samples came out already corrupted from one :

I was about to replace the OKI MSM6295 when I noticed some solder residues on a couple of pins.I magnified the area with a microscope and found a solder bridge that shorted two address lines (pin 20 and 21)

Soder bridge on MSM6295

I removed the bridge and sound was fully restored as well as board 100% fixed.

 Posted by at 8:51 pm