Hi all,
First post here. Long-time C64 guy who also repairs arcade PCBs, mostly mid-80s Capcom, and writes them up at HonchoC64.com. Two recent boards, both awkward in different ways. I put a brief version of this in my introduction thread, but think the details belong better here.
Ghosts'n Goblins, intermittent memory fault
Classic "only fails when it wants to" behaviour, and nothing off-the-shelf would provoke it reliably. I ended up writing my own 6809 test routines: read/write across the addressable RAMs and ROMs, and on a failure drop into a tight loop reading the same byte forever. That turns an intermittent fault into a static signal you can put a probe on and trace back to the device. Crude, but it beat shotgunning the memory. Board now runs on great
Two dead boards, originally one intended as a donor for the other. Between them: a dead CPU, a stopped clock, flaky ROMs and stuck flip-flops scattered across all three decks. Both ended up running, though it cost a fair number of new ICs. The clock and CPU had to come first, since with no bus activity there's nothing to measure and every other fault stays invisible behind them.
While working through Commando I converted all 18 sheets of the original 1985 drawings into an interactive format: clickable, navigable, with IC-level walkthroughs of what each section actually does. Same treatment for Ghosts'n Goblins. The idea was to stop squinting at scanned PDFs and be able to follow a signal across sheets properly.
They're free to use, and I'd rather they were correct than flattering. Corrections on the conversions especially welcome.
I also got a question about the diagnostics ROM I used for Ghosts'n Goblins so I attached the source code for it, which includes build and use instructions. You can also find it on my website.
/Honcho
First post here. Long-time C64 guy who also repairs arcade PCBs, mostly mid-80s Capcom, and writes them up at HonchoC64.com. Two recent boards, both awkward in different ways. I put a brief version of this in my introduction thread, but think the details belong better here.
Ghosts'n Goblins, intermittent memory fault
Classic "only fails when it wants to" behaviour, and nothing off-the-shelf would provoke it reliably. I ended up writing my own 6809 test routines: read/write across the addressable RAMs and ROMs, and on a failure drop into a tight loop reading the same byte forever. That turns an intermittent fault into a static signal you can put a probe on and trace back to the device. Crude, but it beat shotgunning the memory. Board now runs on great
- Repair story: https://honchoc64.com/gng-story.html
- Interactive schematics: https://honchoc64.com/gng/
Two dead boards, originally one intended as a donor for the other. Between them: a dead CPU, a stopped clock, flaky ROMs and stuck flip-flops scattered across all three decks. Both ended up running, though it cost a fair number of new ICs. The clock and CPU had to come first, since with no bus activity there's nothing to measure and every other fault stays invisible behind them.
- Repair story: https://honchoc64.com/commando-story.html
- Interactive schematics: https://honchoc64.com/commando/
While working through Commando I converted all 18 sheets of the original 1985 drawings into an interactive format: clickable, navigable, with IC-level walkthroughs of what each section actually does. Same treatment for Ghosts'n Goblins. The idea was to stop squinting at scanned PDFs and be able to follow a signal across sheets properly.
They're free to use, and I'd rather they were correct than flattering. Corrections on the conversions especially welcome.
I also got a question about the diagnostics ROM I used for Ghosts'n Goblins so I attached the source code for it, which includes build and use instructions. You can also find it on my website.
/Honcho