Hello All! New member here, thanks for all the great resources and discussion on synth repair! I checked the forum but wasn’t able to find any single voice PWM issues on the Juno 106 so I’m asking here.
I have a friend who sent me his Juno 106 because it had a “Bad sounding” voice 4. When he bought it, it had a pretty bad repair done to two of the voice chips and a couple damaged traces where the “tech” probably heated the board too hot to replace the modules. Anyway, I fixed the board for him (Had to run jumpers) and replaced 3 of the 6 voice chips with the AR chips. (I did not calibrate it because he only sent me the module board). Fast forward about 3 months, he called me with an issue where voice 4 was “thin” and “weak” sounding. he swapped the voice chips around and it made no different in the tone of voice 4… Not being professional, I talked him into finding a local tech to do a “propper” repair, but he was not able to afford the tech in his area, so I told him to send me the whole keyboard and I’ll do my best.
FF to yesterday, I calibrated the synth per the service manual, and everything calibrated great until the PWM calibration. On voice 4, the duty cycle for the pulse was only about 8%. Adjusting VR 31 had almost no affect on the duty, and the slider only increased it to about 10%. As I look through the schematic, it appears to me that this might be a DCO issue? Not sure where I might go from here, since the PWM duty is controlled with a single voltage for all voices. I would love some troubleshooting help on this, or if anyone has seen this before. This is partially a learning experience for me, and I’m trying to help a friend out who can’t afford a “real” tech.
Thanks in advance for all your help!