[dmp]

Can you  measure for the control voltage?
If you feed a audio wave to the unit and measure the DC voltage at the attack pot, you should see the control voltage go up as you increase the signal level feeding the unit.

[duantro]

I swapped out a fresh vcr2n, and no difference. DMP are you saying measure the dc voltage at the attack pot, while increasing signal level?

[dmp]

Yes - I would start out measuring on the attack pot (the side that faces the VCR2N) for the control voltage.  You probably will not have any voltage there. If you don't, then work your way back through the sidechain to see where things are getting messed up.
The basic operation is an audio signal goes to the ceiling control, which sends a signal to the sidechain (the ceiling changes a dual voltage divider to adjust the threshold and output together) . The signal to the sidechain  is amplified and rectified to a DC control voltage. That voltage changes the resistance of the FET (VCR2N) in the first 2520 amp circuit, to modify the gain of the amp.

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