Minimoog Model D Issue

[tomorrowstops]

Currently, she's sustaining notes indefinitely in a couple of different circumstances.

Circumstance #1: With the decay switch OFF, if the decay knob is set to zero, the last note pressed on keyboard will sustain indefinitely. When I advance the decay knob to a longer time, the sustain will decrease and disappear. Everything else (knobs/switches/keys) behave like they should.

Circumstance #2: With the decay switch ON, the last note pressed on the keyboard will sustain indefinitely, regardless of decay knob position. Everything else (knobs/switches/keys) behave like they should.

Both circumstances occur with or without the keybed assembly plugged in, so I would assume its not a key contact/buss bar issue.

Thoughts?

[tomorrowstops]

Its also interesting to note that it was fine for a few days, and then I picked up and moved the Mini elsewhere in the room and the issue started. Unfortunately, moving it back didn't resolve the problem, however . So far everything I've look at inside doesn't giveaway any clues - no loose connectors, etc.

[Mesmerised]

You could try reseating the PCB boards inside the mini. Carefully take the boards out, clean the connectors and put them back in. Maybe it's just a problem from the connectors.
If that doesn't help you'll have to look further into the schematics of the env.

[tomorrowstops]

Thats a good idea. I think I'm going to go through and clean up everything at this point. The seller had said it was 'recently serviced' but hasnt given me any details. So who knows. The keybed needs some love (bushings/leveling) anyways. It is nice however, to be back in vintage land. THAT sound! Worth all the effort....

[Mesmerised]

Yeah, I always say that the mini is the Stradivari of electronic instruments. Mine with the older oscillator board has a very engaging sound that gets me every time and puts a smile on my face.
When you're opening it up you could check if the PSU has been recapped (new electrolytics) and calibrated properly to +10V and -10V. (the exact voltages are important in the mini.)
The board connectors are known for bad contact. But after cleaning I didn't have any issues with mine anymore. I took the opportunity to give it two mods as recommended by Moog service: the octave buffer and the deadband mod for the pitch bender. That increased tuning stability a lot.

[tomorrowstops]

I've got the older osc board as well, and it has the same effect!

What did you clean those board edge contacts with?

The power supply board still has big old looking purple caps. Its been a while since I've replaced components on a board, so I'll have to get back in the groove again before fooling with those. I'm just a super casual-level hobbyist!

I'll look into those mods. I also need to clean up the key action with new bushings and some general cleaning/leveling. I'm thinking about going to the optokey, but want to see how my clean up goes before going that route.

[Mesmerised]

I cleaned the connectors with "tuner spray", that's a very non-corrosive deoxit for delicate parts. It can also be used on pots/sliders without damage. With the mini though I didn't clean any potentiometers since turning them each for over a minute already yielded them fully working again.
Except for two: I dismantled the modwheel and pitch pot and cleaned them. Had to replace both though. But I went back to the original modwheel pot, since it has a very special curve and I didn't find replacements. So treat it carefully!

I would recap the electrolytics in the psu. I have rebuilt the power pcb following the newer Norlin plans here:
http://v8media.com/minimoog/Norlin_sche ... -schem.gif

Use high quality replacements (e.g. Panasonic) with high temperature rating, higher voltage rating as they're not that expensive and they have to take a lot of load in these PSU styles.

I did most of the Moog recommended modifications (you can find the originals on the web) but stayed away from changing the filter or oscillators too much. (careful with recapping there!)

Best of luck with your precious mini!