Vintage MS20 MKI VCO issues

Post by **tomorrowstops** » Sat Jun 29, 2024 7:24 pm

So I've been slowly fixing up this MS20. It needed to be cleaned and 3 pots needed to be replaced. But I'm battling one of its original issues, which is pitch/waveform unstableness in VCO 1.

If you listen carefully in the video below, you can hear issues in the first octave. Most notable is G-C, which you can clearly hear what sounds like FM happening, but at different speeds depending on the note. MG Freq, nor VCO2 fine pitch affects it. Does it across all waveforms. VCO 2 doesn't exhibit any of these behaviors. One key (F) sends pitch all over the place every time using VCO 1, but only once and a while on VCO 2. This *might* be a key contact issue though; I haven't taken it apart yet. The overall pitch tracking is pretty spot on in tune.

I know these older MS20's are known to have oscillator and FM bleed (I've owned 2 over the past 10 years), but this sounds wackier than I remember.

Thoughts?