[sdiy] Oberheim 4-voice Mixer/Output Module Schemos?

[Eric Frampton]

So.....

I'm finally getting around to working on my 4-Voice. This one came to me partially (mostly) operational: 2 of the 4 SEMs are good; #3 has a constant high frequency squeal and doesn't respond to CV; #4's LED is stuck on and doesn't make any sound at all. The Mixer seems to be OK and the keyboard module seems to be mainly OK. With only 2 of the 4 SEM's working there's a little bit I can't test yet.

It has the programmer, which although not working 100% doesn't seem to be affecting the SEM's - whatever issues they have move with them when I re-patch them to different programmer outputs.

This particular unit has a couple of factory mods that are interesting. It belonged to the vibes/marimba player in the band Starbuck ("Moonlight Feels Right"), and has a custom marimba-CV interface via a multi-pin connector on the back. It appears to be polyphonic as well, since it has a big ol' A/B switch with the keyboard that comes before the keyboard module. It also has some sort of custom interval switching (instead of just an octave) and an external LFO of some sort. More poking around will be required there...

I've found copies of schemos for everything except the mixer/output module. Does anybody have those that they can scan and post/share?

Also, was there ever a formal service document for the 4-Voice? I've found the manual for the individual SEM's (which includes some calibration info), but haven't seen anything about trying to calibrate anything else (keyboard module, programmer, power supply).

Thanks,
Eric