keropi wrote on 2021-05-18, 20:13:
I would start by reflowing the connector anyways - there can be hairline cracks that are hard to spot
Thanks for the reply. I have more information: although I haven't yet had a chance to try what you suggested (something I plan to try unless this information yields different advice), I did previously check for continuity between the pins on the connector and the solder on the bottom of the board and it is there in all cases. If I recall correctly I was also able to establish continuity between the connector pins and the solder connections for the coils that the connector runs into. I have not been able to establish continuity between the connector and the resistors or the optocouplers that follow in the circuit path, but I think that is more a matter of either my not having the right probe or my not knowing how to do it with the particular sorts of mounts these components have on the board. (I couldn't establish continuity between the pins and these components for the working connector, either.)
However, I remembered this morning that when I did the self test, the unit reported a result of "OK" for both IN1 and IN2. The NG (bad) result was for the third option, "422," which I think is the serial port? I'm not sure I understand this correctly, though. In any case, the two ICs the service manual points to for this result are the subprocessor, into which all the inputs (including the working one) go and the IC for the serial port. This might suggest the unit is set to read the serial input rather than the MIDI in, and I have come across one case online where a person had a similar problem to mine and the problem was the switch which swaps between the serial and DIN port. In that case, the switch was bad and so it was "stuck" on the serial in.
In my case, though, I've tested the switch with the meter and when I move the switch, continuity does change between its pins. In other words, the switch seems to be working correctly.