Powers on with Korg KA350 AC adapter (not included) and sometimes makes pitched sounds that are effected by the knobs. The envelope gets stuck on certain keys and the sound fades away until you turn it off and on again. I twisted and broke off most fake nuts around right-panel 1/8" jacks (thinking they were actual nuts) and saved them in a bag. You may or may not want to glue them back on. They serve no functional purpose.There was a short, red wire attached to nothing inside which I also saved.

Q&A:

1. When you plug it into a computer via USB, does it show up as a midi interface named “ms-20” or similar? No. I don't see any signal indication lights on MIDI to USB device when I press a key on the MS 20 Mini.

2. Does it respond at all to midi in signals either through USB or the 5-pin din port, and do you see the same stuck envelope/fading symptoms? When connected to another keyboard using a standard MIDI cable, the envelope light does not get stuck on but the sound fades away after a few secords.

3. If you set the osc 1 and 2 levels to zero on the mixer and then set the LPF freq to about half way and the resonance completely up, can you hear the self-oscillation of the filter when pressing a key or sending midi to it? With both filter peaks and envelope release times set to 10 and hold time at 10, it self-oscillates for a while then fades out.