Vintage Synth Repair

Hi everyone,

Recently my Odyssey has begun experiencing Oscillator drift. It's related to the LFO. Even when LFO modulation is set to minimum, there is still a small amount of modulation making it impossible to play notes at a stable pitch. When I speed up the LFO the modulation speeds up accordingly, although the Oscillator LFO modulation sliders are set to zero. This means I can't get a stable pitch out of it, and this affects both oscillators. It's only slight but enough to make it unusable as a musical instrument.

Anyone got any ideas for a fix? I'm hoping it's nothing too serious.

thanks,
Ian

Hi, Ian:

First, plug a 1/4" jack into the pedal socket on the rear of the Ody and set the VCO2 LFO/S-H Mixer/Pedal switch to Pedal.  Pull VCO1 and Noise in the mixer down to 0, open the VCF all the way (no Resonance) and set VCO2 to full.  See whether the problem goes away for VCO2.

You could then try (temporarily) de-soldering one end of the 100k resistors R38 and R40 on the B-1 board.  This would remove the LFO from connection to the VCOs and you could see whether the problem goes away for both VCOs.

If so, the problem almost certainly is in the two 100k audio taper sliders P6 and P10, although both of them going at once would be odd.  Might just need cleaning out to get some gunk out of the bottom end of them.

The only connections between the LFO and VCOs 1 and 2 are, respectively, S3, P6, R38 and S6, P10, R40.  No other way for LFO signal to bleed through to the VCOs.

David