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Now that we know that we have good voltages let’s have a look at the mainboard. The CBM floppy drives are peculiar in that they are multi CPU systems. The 8050 and its relatives have two 6502 CPUs. One, together with some SRAM, ROM, and a 6522 drives the IEE488 bus, also known as GPIB.
The other 6502 drives the floppy mechanisms and decodes the GCR data.
The ICs have a bit of corrosion on some pins. But luckily all the chips can be replaced if necessary.