Posted By
JamesC
on 2017-10-31
17:47:32
|  Re: Commodore 16 and 'Device Not present' error :-(
Yes, there are a set of diodes in line between the serial bus connector and the CPU. To test, apply 5V at each pin of the serial bus connector (where you attach the disk drive cable), and see what voltage comes through to the CPU's side of the corresponding diode.
Refer to the bottom of this technote.
When I said no single chip controls the serial bus, I meant that we cannot just say "replace this one chip and be done". Since the 16 "boots up" I seriously doubt there is anything wrong with the CPU.
It's much more likely that the serial bus connector itself has developed a loose connection, which will be revealed when you try to pass voltage through it.
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