minimoog model D VCA issue

[coolcatguy]

i'm an experienced tech fixing up my father-in-law's minimoog D #4678 - he is the original owner and kept it in a clean, safe environment but hasn't touched it in many years. it's having some issues that i'm attempting to rectify and am a little stumped at the moment and want to get a second opinion before i replace unnecessary parts.

first things first:
caps all look good and voltages on all 4 boards check out correctly but the output is extremely weak. A440 comes through loud and clear and the signal for the synth sounds good up to the VCA so i know the problem is there... any thoughts?

[MC]

The Minimoog actually has two VCAs.

Check the rear panel loudness jack. With nothing plugged in, it is normalled to a fixed CV to the 2nd VCA to keep it active. The 1st VCA is for the envelope generator, the 2nd one is for volume modulation IE using a pedal or joystick or tremolo LFO. If the normal contact on the loudness jack goes bad, the 2nd VCA won't get its full fixed CV and won't allow full signal to go through. Very common fault.

The A440 is routed after the VCA. When you turn it on, it is not affected by the VCA.

[coolcatguy]

The Minimoog actually has two VCAs.

Check the rear panel loudness jack. With nothing plugged in, it is normalled to a fixed CV to the 2nd VCA to keep it active. The 1st VCA is for the envelope generator, the 2nd one is for volume modulation IE using a pedal or joystick or tremolo LFO. If the normal contact on the loudness jack goes bad, the 2nd VCA won't get its full fixed CV and won't allow full signal to go through. Very common fault.

The A440 is routed after the VCA. When you turn it on, it is not affected by the VCA.

gotcha. i mentioned A440 to make it clear that the headphone amp and the main outputs seem to work fine. as for the 2nd VCA, i am getting around 7.5V on pin 10 and when i plug a jack it it breaks that connection so i think the contact is ok. i checked pin 9 (contour input) and it's stuck on -.5V and the envelope generator isn't responding to the keys so i guess the next place will be to check will be the key assembly and contact buss.

[hip808]

It's been a while and wondering have you fixed it?

I am having the same problem that goes on and off - very weak output volume but A440 tone is ok. Sometimes the problem goes away by itself.

Earlier I thought it was the problem on board 4 (VCA) but after reading this thread, with some Dexoit, I tried to plug in and out the loudness input a few times. Not sure if this helps but the problem did went away for a while. However, it always comes back. How should I confirm the problem? Should I replace the input jack socket?

[Minimoog89]

It's been a while and wondering have you fixed it?

I am having the same problem that goes on and off - very weak output volume but A440 tone is ok. Sometimes the problem goes away by itself.

Earlier I thought it was the problem on board 4 (VCA) but after reading this thread, with some Dexoit, I tried to plug in and out the loudness input a few times. Not sure if this helps but the problem did went away for a while. However, it always comes back. How should I confirm the problem? Should I replace the input jack socket?

Do you have an original or reissue model D? This sounds exactly like the issue I've had pretty much constantly with my reissue since I brought it. Although now it won't even turn on, so I can't test it. Must take it for repair!