Denial

Hi,

I've been trying to repair an early VIC-20 model, with the same motherboard as the VIC-1001, with no luck.


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I've already checked the chips identified in the Carlsen guide as blank screen culprits. All of them are ok or replaced with working ones.

One special feature of this motherboard is a tiny piggyback near the VIC chip. Take a look at the pics:


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And with the piggyback desoldered:


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(you can see it here with another VIC chip, I don't want to risk the original one on the tests)

What does this little board does? the motherboard pictured in the Giacomo book does not have it and instead has some other passive components soldered in it's place.

Any clue or guide on what should I check now?
I can take new pictures of the motherboard or screen if needed.

Thank you!
Roberto

Not sure about the board, maybe an output amp. I would break out a scope and start checking for clock, reset and data on the bus.

I'm getting 404's (link broken) on all those images.
General path I follow when troubleshooting black screen failures:
Start with voltage rails, then RESET pulse and clock.
Then confirm ROM access.
Check I/O then RAM access.
Once they're working as expected, look back to VIC, and forwards into video output circuitry. (I've had a C64 blank screen caused by a failed RF modulator before!)