May 262016
 

I got from New Zealand this genuine Splatterhouse PCB for a repair:

Splatterhouse_PCB

Upon boot the board was stuck on a “ROM TEST START !! PLEASE WAIT…” message displayed upside down :

issue

From my past experience I know for sure this issue is caused by a bad ’64A1′ custom replaceable with a programmed Hitachi HD63701 MCU (plus a patched ‘VOICE0′ ROM in order to handle two custom opcodes of the ’64A1’)  following this procedure:

Namco System 1 custom ’64A1′ replacement

But in this case, as you can see from the above picture of the board,  the owner already replaced the ’64A1′ (and at same time  patched the ‘VOICE0′ ROMs using an hacked 1Mbit JEDEC EPROM in place of a non-JEDEC one ) and this didn’t fix the issue.For first I reverted the modification the and reinstalled the original custom ’64A1’.With this configuration the board successfully booted into game although some sound samples were bad.This lead me to think that there could be some problem is the data bus of the VOICE ROMs which prevented the HD63701 MCU to correctly read the patched data causing the missing boot. :

VOICE_ROMS

So, assisted by schematics, I went to check the involved circuit and found that pin 20 (data line D6) of the VOICE ROMs (Splatterhouse use only four of them to store samples) was not daisy-chained as it should have been:

VOICE_ROM_DATA_BUS

In the above snippet of schematics you can see (red mark) where extactly trace was interrupted.I simply used a bit of AWG30 wire to restore comnection:

patched_PIN20_VOICE_ROMS

This fixed completely the game using both the original ’64A1′ custom and the HD63701 MCU.End of job.

 Posted by at 8:19 pm