I was a little afraid to try to advise since this is such an expensive piece, with so many dollars potentially at risk. If one is not a very experienced tech then one should tread very lightly with a unit like this.
Even though the circuit is in essence pretty simple, there are ways to go wrong. The problem could be caused by the switch, wiring, inductor network, a capacitor, a previous repair, etc. For an experienced tech, patient, methodical fault finding could probably identify the problem in an hour or so but it seems difficult to give easy to follow, safe advice for fault finding. It might be helpful to verify the accuracy of the frequency settings that do work, along with cut/boost amounts.
The problem might or might not be a capacitor. Don't do anything that might damage the potted network, because it's basically irreplaceable. It might be difficult (or impossible) to remove and repair it without doing even more damage. Sometimes, if the exact fault is known, a part can be added inside the main chassis to repair a fault in the network.
If you can, check the other frequencies and cut / boost amounts carefully. I'll look at the schematic and see if I can offer any other suggestions.
(I edited this reply a couple of times because I wasn't comfortable with some of my original comments.)
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Topic: Pultec EQP-1a EQ cap replacement (Read 14595 times)