Or imagine a Drake R8A receiver, described as "guaranteed NOT to work" that a friend picked up. It can be tricked into working, but it gives a "PWRLOS" display most of the time, and there is no discernable cause. Thanks to the obscure NEC uPD78213 cpu actually being available and documented, and having no internal rom... it's time to write a disassembler[1] (or later find out that MAME has one[2] thats pretty good), look at all the schematics, and figure out how the firmware works.

*Still working on the disassembler, because I can eventually make mine interactive, add labels, comments, etc.

[1] https://github.com/mikewarot/Res78213

[2] https://docs.mamedev.org/debugger/memory.html#debugger-comma...