Not much happening on the DIY front for quite a while, but now I can haz a model 2800 whiteface Arp Odyssey \:D/ Yay!
What a classic synth, I have no doubts that this will swiftly become my precioussssss-sssss. Downside, it’s going to need a whole bunch of repairs. Keyboard bushings, sliders, damaged components, you name it. Probably every bit you could expect to be broken in a synth that’s +30 years old.
So repairs it shall be then. To get started somewhere, I gave the internals a quick glance to map out the most “obvious bits”. Someone had been servicing (or “servicing”?) the synth previously to say the least; there were some extra components added to the solder side of boards A and B and the power supply cable had been swapped.
Extra components aren’t really much of a problem at this point since I’ll be comparing all of the boards against the schematics at a later stage, but the power supply cable needed to be sorted out immediately. The original cable had been replaced with a 2-pin cable leaving the case/frame ground totally disconnected, despite this is clearly indicated in the schematics. As the case is also used as audio ground, maybe someone had problems with ground noise and did a (bad) fix.. Who knows. Anyway, in a short-circuit situation this having the case not connected to the ground could make the casing hazardous to touch.
In it’s original configuration the power cable is soldered directly to the PSU board: As this makes the synth a little more harder to service on-the-fly (if the cable is damaged), I chose to mod the PSU/case for a schuko compliant connector.
Here, I had to leave the lower edge of the cutout to an angle to fit the blade in the cutout. Luckily the metal used for the casing is really soft and easy to cut, so filing off the excess metal (to make a rectangular cutout) wasn’t much of a task.
Despite I had to cut the case and the PSU board to make the connector fit, I felt that doing this much irreversible modding was mandatory. Just for the sake of electrical safety if nothing else.. In order to keep the cutting to bare minimum, I decided to use the existing PSU cable hole. Unfortunately this meant that I also had to cut a small piece away from the PSU board. I had a spare EMI filter module (salvaged from some laser printer) lying around so I put that in as well. Cleaner power supply feed is never a bad thing either :).
A further option would’ve been to lift/isolate the internal system ground from the power input frame ground. Like said, the case of the Odyssey is used for both system ground and the power frame ground. This is also utilized in the output jacks, there is no need to use a wire for running the ground to the connector via a cable when the metallic case connects to the synth case.
Before connecting the PSU board to the EMI filter, I removed the board from the case and washed it with some PCB cleaning liquid. After drying up (compressed air ftw!) I measured the electrolythic capacitors, tested / calibrated the PSU and put it back to the case.
Oh and I seemed to pick up on how to add captions to the pictures. Didn’t take much more than the +60 posts on this blog already :)