Yamaha DX7 Sustain Repair?

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Joined: Sat Apr 29, 2017 3:26 am

Yamaha DX7 Sustain Repair?

Post by opcode » Sun Nov 05, 2017 5:32 am

Hello! I'm wondering if anyone knows how I can troubleshoot (I have a scope and voltmeter!) or solve this issue :

I have a nicely functioning DX7, with a caveat -- It must have (any) sustain pedal plugged in, or else sounds will infinitely sustain when keys are pressed. When a pedal is plugged in, all is well.

I've scoured the depths of the interwebs, and have tried everyone's suggestions. Pressing the sustain pedal and powering off the synth, reversing the pedal polarity and power cycling the synth, pressing a key when the synth is powering on, and every permutation of those things, heh.

At this point I'm thinking it's a hardware issue -- but don't know how to troubleshoot it from here. The service manual is pretty brief, and dosnt mention petty sustain issues. When I open up the DX7, I do see a ceramic capacitor and resistor right by the sustain input. Would anyone happen to know what values I should verify those to be with my multi/voltmeter, or what might be wrong here?!

EDIT: Thanks to the help of a member of another forum, I was able to diagnose the issue :

I compared the sustain solder joints to the jack next to it (portamento) and found some differences!

I ended up sticking a tweezer in the sustain port, and pushed some metal plates together until they touched again, and now all Is well!

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