MiniMoog D Oscillators dropping out

[eric coleridge]

My Mini has had a few minor issues for awhile, but only recently, VCO 1 and 3 have been dropping out of audio range. It's intermittent, after leaving the power on for quite some time, VCO 3 usually comes back in, and VCO 1 occasionally. I can actually hear the VCOs rising in frequency as they come back in.

This sounds like bad capacitors, right? But, the VCO timing capacitors wouldnt be electrolytic, would they? Wouldn't they be ceramic? I'll have to look at the manual.

I just thought I'd see if anyone here has had this problem and fixed it already? Although, I do a lot of synth building, I normally prefer not to work on my Mini.

The other minor issue with this Mini is a sort of random portamento thing that happens when I press a key with only slight pressure. I once cleaned the key contacts and buss bar, but it didn't fully solve the problem. Maybe it's dirty contacts on the glide switch? Any other suggestions?

This is an early, '72-'73 Mini.

[MC]

Your capacitors are fine. They are polystyrene and will have a long life. If the caps were bad, you would hear nothing. If you still hear oscillation, the caps are good.

The problem is likely the expo converter, probably the 3046 tranny array or the tempco resistor. The latter are harder to source these days.

How did you clean the buss bars?

There are two sets of contacts in a mini keyboard. The CV buss MUST make contact before the gate buss does, otherwise you get the behavior you describe.