First of all I want to thank JROK for providing me all the technical info and allowing its public release, without his help I would not have ever made.Let’s start with the story.

Some time ago a  friend of mine sent me his Splatterhouse PCB bought as working saying it got stuck upon boot  on ‘ROM TEST START!! PLEASE WAIT..’ message displayed upside down on a screen filled with red zero.So I started to investigate on the net and found that usually this kind of issues are caused by a faulty custom chip marked ’64A1′ @M4 on ROM board.This was confirmed by swapping this IC in another CPU board of Galaga88 with this missing component , in this case I got an ‘EEPROM ERROR’ message which is a further proof of the fault.

Thanks always to JROK we know that this ’64A1′ custom IC is nothing else than a HD63701 MCU with the exception of two custom opcodes not present in original part.You can go deeper into technical reading here:

https://www.jrok.com/hardware/cus60/cus60_an_owners_guide.html

So, programming a blank HD63701 MCU with the available dump from MAME won’t work due the presence of these two custom opcodes.So, patching a ROM is needed.

In the specific you have to change three bytes in the ROM  “VOICE0” at a specific offset.For example :  in Splatterhouse the offset is $FA8B and the new HEX values are “20 01 56”.

The string to search for in HEX is  “B7 C0 00 6E 00” and the first 3 bytes must be changed to  “20 01 56”

The patch seems to be needed at offset $FA8B for most games, but not all. Here’s a reference table :

Tank Force – $FA29
Blazer – $FA8B
Dragon Spirit – $FA8B
Galaga 88 – $FA8B
Marchen Maze – $FA8B
Splatterhouse -$ FA8B
Rompers – $FA8B
Blast Off – $FA8B
World Court – $FA8B
World Stadium (and WS ’89, WS ’90) – $FA8B
Bakutotsu Kijuutei (Baraduke 2) – $FA8B
Beraboh Man – $FA4E
Dangerous Seed – $FA8B
Face Off – $FA29
Pisto Daimyo no Bouken – $FA8B
Puzzle Club – no voice ROM !
Quester – $FA1B
Souko Ban Deluxe / Boxy Boy – $FA8B
Yokai Douchuuki (Shadowland) – $FA8B

So, it was only matter to find some real blank HD63701.My first attempt failed since I bought as new some ICs that they turned out to be already programmed and, since they were the plastic HD637B01VOP one-time-progfammable version, they were unusable for my purpose.But then I was luck and found some HD63701VOC UV erasable ones:

So, it was only matter to program one of these MCU with MAME dump using my Hi-Lo Systems ALL-11C EPROM programmer and, at the same time, replace the ROM ‘VOICE0’ with the properly patched one.Once done, I had confirmation of what the good JROK said about. Operation  ‘NAMCO custom 64A1 replacement’ accomplished.

Got this original Konami G.I. Joe PCB from Ebay as not working.Looking at the auction picture I could see the ‘051550’ SIL custom broken in half, this was confirmed once I received the board:

For the uninitiated, this custom is of vital importance since it generates the master RESET for the whole board, infact 68000 CPU RESET line was stucked LOW and I got only a static screen:

I had many Konami faulty boards for spare so I took this custom from one of them and, after replaced it, the board resetted properly but with an error on VRAM @16K:

Desoldered and test the 6264 RAM out-of-circuit confirmed it as bad.With a new RAM game was fully playable  (also with sound which is quite rare as this board uses the ‘054986A’ hybrid custom module) but something was wrong :

 

like some colours were missing from certain backgrounds and this was confirmed also by the color check I ran in TEST MODE comparing the output with the one from a working board:

 

Color RAM was OK as reported by initial test so I start to suspect the ‘053251’ ASIC since I had a similar fault on a Bell & Whitles PCB.According to MAME this ASIC is a palette/priority chip :

So this convinced me to replace it.And I was right since colours came back to normality:

Gameplay was fine now but some of the sound FXs were muffled and distorted.It could not be due the ‘054986A’ hybrid module since the issue was limited only to some FXs so I started to check the audio circuit (commanded by the usual Z80 CPU).When I piggybacked the 6116 SRAM @6C all the sound FXs were restored so I desoldered the chip in order to test it out-of-circuit:

 

RAM was really bad though this fault was not reported by initial RAM/ROM test.Not satisfied, finally, to top it all I recapped (with tantalum capacitors) and socketed the ‘054986A’  sound hybrid module’:

End of job.