Repair Roland TR-909 Drum Machine Reparatur Service26. Oktober 2018
TR-909 OS Version 4 Service10. November 2018
Korg Polysix vintage analoge synthesizer. Some of the lower keys of the keyboard weren’t working. The output jack was dead and the headphone sometimes crackling or distorted. I suggest to add the Tubbutec modypoly installation.
Since the synth was working, I first ordered the modypoly from Tubbutec, which came in quite quickly. I started tracking down the “no output” issue. Since the headphone was working it was a quick find, that the Off/Hi/Lo switch was responsible for that issue.
But after cleaning there still was no output, but the switch was working now, mmmh? Ok, looking and probing a bit more in that area and I found (what else?) my first of a few cold solder joints.
And voila, output was working. That cold solder was also one of the reasons for a “kind of” distorted output. But playing all six voices I found, that two voices were out of adjustment in volume and resonance. Ok, I thought, lets calibrate all voices, but that wasn´t successfull in the first instance. Some potentiometer had a strange behaviour, something like (guess what?) cold solder joints. After fixing these cold solder joints all six voices sounding great and I could go ahead with cleaning all the rest of the switches and potentiometer. Tactiles were ok, so no replacement here. Then I took a look to the keyboard and (ooooh, nooooo) I found out, that someone before me had scratched the contacts and scratched off the surface protection.
These contacts were quickly oxidized and made no (or no good) contact anymore. The “other side”, the carbon pads looked and measured good. Ok, I thought, let`s do some gold plating here. I cleaned everything, grabbed my “gold plating kit” and did a few layers of new gold onto these contacts and so I got them all back to life.
Last but not least I performed the modypoly installation, another calibration procedure and now the Polysix is working great again.
Like always I share with you my “in depth” pictures, which I took for my own documentation. Enjoy.
I’m documenting repairs for my reference and yours.
I do synth restorations and repair with a specialty in vintage synthesizers, drum computer and other vintage gear, based in Düsseldorf, GER. Get in touch about your synth situation!
There are lethal voltage exposed in electronic devices. Unless you know what you are doing, don’t try this. If you following along, you doing so at your own risk.