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Hello from Honcho, two 1985 Capcom repairs

HonchoC64

HonchoC64

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Hi all,

New here, so a quick introduction. I'm a passionate C64 retro dude, but I also repair arcade PCBs and write the results up at HonchoC64.com, mostly mid-80s Capcom hardware. I've just finished two boards that fought back in very different ways, and thought this crowd might get something out of them.

Ghosts'n Goblins had an intermittent memory fault that only appeared when it felt like it. Nothing off-the-shelf would provoke it reliably, so I wrote my own 6809 assembler test routines to corner it. The board now runs flawlessly, all-original hardware, no repros.
Commando was the bigger job. Two dead boards, originally meant to donate parts to make one working one: dead CPU, stopped clock, flaky ROMs and stuck flip-flops spread across the three-deck stack, roughly 250 chips to work through. Both ended up running, though it cost a fair number of new ICs. Along the way I converted all 18 sheets of the original 1985 schematics into an interactive format, with IC-level walkthroughs of how each section actually works.
The schematics are the part I'm most pleased with. Clickable and navigable versions of the originals, so you can explore at component level instead of squinting at a scanned PDF. Hopefully useful to anyone else taking on these boards.

Feedback and corrections very welcome, especially on the schematic conversions.

/Honcho
 
These are both fantastic writeups @HonchoC64 ! I'm very impressed with your technical knowledge and thorough documentation. Any chance you'd be willing to share your memory diagnostic ROMs for Ghosts N Goblins? It would be very helpful for other folks performing diagnostics on that hardware.
 
ShootTheCore said:
These are both fantastic writeups @HonchoC64 ! I'm very impressed with your technical knowledge and thorough documentation. Any chance you'd be willing to share your memory diagnostic ROMs for Ghosts N Goblins? It would be very helpful for other folks performing diagnostics on that hardware.
Click to expand...
Hi, thanks for the kind words, glad you liked it.

To be honest, the diagnostic ROM is dead simple assembly and probably not much use to anyone else. All it does is read and write the various addressable RAMs and ROMs, and on a failure it drops into a loop reading the same byte over and over. That makes it trivial to put a probe on the bus and see where things went wrong. I needed something this crude so I could tap the bus and identify exactly which RAMs and ROMs were misbehaving. The alternative was shotgunning the lot, which is a blunt way to find one bad chip.

Anyway, here's the source, with instructions for building the ROM binary and where it needs to go. The write-up may be the more useful part, since it's genuinely easy to write your own little routine instead of using mine.

/Honcho
 

Attachments

I added this to the story page as well in case others will find it useful. Never thought of it so a good call out :)
 
Welcome @HonchoC64. Great to know someone here has joined who has experience on fixing pcbs. Just a quick question when you have a chance: my Tatsujin Oh (Truxton) PCB stopped working after there was an electrical spark/problem in the PSU. It is dead. Any suggestions on what might be the issue? It looks it took a voltage hit from the power supply through the Jamma harness. Thanks if you get a chance to follow. Welcome again!
 
ner38073 said:
Welcome @HonchoC64. Great to know someone here has joined who has experience on fixing pcbs. Just a quick question when you have a chance: my Tatsujin Oh (Truxton) PCB stopped working after there was an electrical spark/problem in the PSU. It is dead. Any suggestions on what might be the issue? It looks it took a voltage hit from the power supply through the Jamma harness. Thanks if you get a chance to follow. Welcome again!
Click to expand...
Hi there! With a bit of hope it's an easy fix, but hard to say without checking the board. Should be easy enough to establish if the 5V that powers the board gets through to the ICs themselves, that would be the first test. Basically establish if your board gets power, or if the fault is with the power supply. If power is OK you normally gets some form of output on the screen that can help, but as I said, not easy to establish without checking the board. I normally check the power, the clock and if the main CPU to see if it boots up as expected, which often requires you to check the output from the CPU (e.g. reset signals, address and data bus). This is obviously a bit more tricky to do, but if you have a PCB with power and a blank screen you need to start tracing which IC fails and for me the CPU is the first thing followed by ROMs and RAMs to ensure it actually gets the first part of the code running.
 
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