Hi all, recently whipped out my pops mini in hopes of a restoration. Everything worked upon first trial. However, after a few days of playing on it and just having fun…the second oscillator seemed to “get stuck” about an octave lower than the 32’ range. it still tracks, the pitch changes, responds to tuning, waveforms change…just seems to have gotten stuck way below 32’. Its been a while since ive last repaired a mini and im currently searching for all my literature on the model d. I thought id ask on the forum before i muck something up.
its serial is in the 6000’s and no mods, or upgrades have been performed to it. it is entirely stock.
any ideas of where i should begin looking? i was leaning towards a transistor or a resistor type issue. Seems fairly easy since…it stopped working after a few hours of play…after a few years of sitting dormant.
I am having similar trouble with number 3 being a semi tone too "high’.
when I first tuned up the thing using a guitar tuner, I thought the highest a was a8 rather than a7 as I put osc1 an octave too high. I realised this after trying to get the others. I then got a frequency counter and using it for 1 managed to get all in the correct range except 3 which is a semi tone too high. that problem is currently under investigation.
for my issue it has been suggested by Alien666 to test the IC’s for that particular osc.
athough Im not much help I wish you luck and would be intersted in what you find.
One question, moogmymellotron: when you switch octaves for OSC 2, is there any change at all in the pitch of OSC 2 ?
If not, then it could very well be IC 2 on the small buffer board #6 that is bad. It’s an easily found 741 op amp. That buffer board is at the top of the casing, behind both board number 1 and 2. It contains three such op amp chips that act as octave control voltage offset buffers. They’re known to fail after close to 40 years… I keep a few in stock, just in case one of them in my Mini should fail. There are 11 of them in a typical Mini with an old oscillator board like ours.
I will try replacing the op amps immediately. The pitch does not change when I switch te octave settings it does however track pitch across the keyboard. It almost seems an octave too low when compared to the other oscillators though.
If you decide to put some IC sockets when replacing those chips, make sure you choose good quality ones with round legs. Not the cheap type with flat ones. You’ll avoid further problems down the road.
I wish you success in your troubleshooting/repair.