Yamaha Modx7+ Not Powering On

Synth Repair
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1

I bought a Yamaha Modx7+ that was admittedly non-functioning when purchasing. The seller had spoken to a local repair guy that was sure it was the jack board (Part #10056). I bought it, opened it up and tested it.

Power solidly enters the jack and through the wiring harness enters the jack board. But any connector past that, any connector going out of the jack board gives incredibly weak voltage, nothing above 0.60V.

The jack board has GND and +12V spots on the board. The GND served as a solid ground while testing but the +12V won’t show voltage above 0.60V.

I’ve tested all connector pins on the jack board with all other wire harnesses disconnected and do not get any jump up in voltage anywhere.

I did order the replacement part, but it did not fix it and all tests give the same results.

I have tested with two power supplies. One Yamaha that is 12V, 1.5A. And one other that is 12V, 2A. I have verified the second one works fine by using it with another synth.

Is my testing even viable? Is it possible that the replacement board I got is bad?

2

You might want to test the board power rail and see if there’s a short.

The power supply might shutdown if it detects a short circuit.

3

Sounds like a shorted tantalum capacitor, the bane of the repair industry.

keep testing each capacitor in that power line to find the one that’s shorted.

If you cant test each cap, then unplug each board from the power supply and see if the problem is secluded to one of those, or the power supply itself.