mine refuses to talk to the chart cartridge but works in every other respect, si I would be happy with an old cheap C80, perhaps with a broken screen, that could be canibalised
I take it you have done the two obvious tests first
1) out the chart card into another C80 (or equivalent that takes the Compact Flash (CF) type cards
2) try a different, known working chart card, into your C80?
No help to you but that was exactly how mine died a few years ago. Chart card was OK and it would not work on another known working card. Could not find anyone who would fix.
i have a C80 available. I put a new screen in it however it would not connect to radar and the plastic screen protector is scratched. Other than that it works flawlessly