Oberheim OB-8 Refurbish - Osc Calibration

Hey everyone,

Have recently taken on refurbishing an older model OB-8 that I received a couple years ago that was supposedly DOA after a botched MIDI installation.

Upon first opening it, I noticed the ribbon cable from the MIDI board was not seated properly and causing it to hang up upon power on. Once I replaced and reseated the cable, the unit turned on and made sound, but the voice, envelope and filter tracking were all over the place. I started the process of replacing all trimmers and Ecaps and then started the calibration process.

I moved through the calibration manual till I got to the Osc1/Osc2/Fenv calibration and noticed none of my test lights were lighting up (which they did properly when calibrating the bend box).

This is supposedly there to indicate a failed/failing osc, however, I feel it is inaccurate. I can get sound out of all 8 voices (although now very, very low, which is another issue i’ll figure out later).

I have also scoped each osc and seen the Tri/Ramp/Square coming from each CEM3340. All power rails are properly set at +/-15 and +/-5.

Wondering if there is a situation where the test led’s aren’t necessarily indicating the functioning of the oscillators and if there is perhaps a way to tune them by ear or get the test LED’s functioning again.