Moog Music Forum

I have a circa 1974 Model D with Oscillator 1 acting up. It will intermittently become unstable, the pitch will start to waver, and then suddenly shoot up out of hearing range. At first I thought it was shutting off, but it is in fact still running, only at about 25K Hz! It will show a nice stable waveform sitting about 25K, with the square edges rounded off to a slightly deformed sine wave. It will then suddenly glide slowly back down to normal, before setting off again. The other 2 oscillators function fine through all this, so the problem is obviously on the Osc 1 board ... I think! Being as this is my first experience with a Minimoog, is there a most likely culprit to look at here? Thanks!

Possibly due to a bad contact on the oscillators board connector, or an intermittent contact in one of the tuning trimpots for that oscillator.

First, I would try to tap (but not try to turn) with a small wooden toothpick inside the 2 holes at the top right (OSC 1 tuning trimpots) to see if that causes any change. If so, then it's a question of cleaning those trimpots.

If not, then I would open the back of the Mini, with the power cord disconnected, and unplug and re-insert (re-seat) the oscillator board.

Oh, and welcome to the Moog forum.

Thanks for the tips, and the welcome!
I've discovered that the three range trimpots have been replaced by someone with less than stellar soldering skills, leaving the solder pads in pretty rough shape. As you suggested, this seems like the obvious place to start. I may have to run jumpers to get this to work again ... will report back!

Re-soldered, ran some jumpers across the damaged pads, and cleaned the trimpots ... all is good now, this thing sounds so sweet!