Rhythm Active eBay store.
The repair itself was probably the fastest I've ever done, largely due to the fact these things are built so well, and have such a great service manual (see Analogue Renaissance). To open it up, you just have to unscrew 2 screws on either side of the keyboard, and voila.
Next I disconnected the cable harnesses on the "module board", unscrewed it from the keyboard chassis, and de-soldered the offending VCA ICs.
|One of the VCA chips|
For this to work well you need a good, hot, solder iron, and fresh solder wick. It literally just wicks the solder right out. Sometimes you can't get the last little bit out, so what you do is apply more solder back to the joint, then try the wick again. It's a cheap, effective way to rework. I've seen other people poo-pooing this technique on the internet, but don't listen to them. It works fine for these older board with really big holes, and small pins.
Then I wacked the new ICs in, soldered them up, and trimmed the legs.
Got rid of the flux residue with a special cleaning agent and bam!
Then I powered up the keyboard, ran the test sequence, and confirmed the chips were all working properly. After this I performed the calibration procedure described in the Roland service manual. You're meant to do this when you install new chips, as it's an analogue system, and the parts can have a bit of variance in their performance. Basically the procedure "tunes" the keyboard voices, so they all sound similar, and stay in pitch. To do this you need an oscilloscope, a multi-meter, and a frequency counter. I cheated and just used the frequency counter on the oscilloscope, but I don't think it really matters.
Most importantly, I now have a fully working Juno 106. It sounds like the future! If any of you out there have a stuffed Juno - go ahead and fix it. It's really easy, and they sound awesome!
|Adjusting the potentiometers|
|Measuring the waveforms|