Hi Terry, please excuse my absence. The popping sound in the MC-240 has been ID'd and fixed. I took your advise and check the resistors. I found one that was suspect. There are two of these (3.3k) that seem to run in parallel with two cooresponding 100uf, [3 (or 12 volt), the caps say three, but some "Clinton" style manual says 12 volt]. I had not previously replaced these caps on the "capacitor board" as they were coated white and through me off. Replaced them, and I'm now good to go. By the way, I have the ability to take two of my 100/30 filter cans up to 140/30 (you know the ones!) What do you think about that? What would it accomplish? You are the best. Thanks again. George