Hi Marshall,
Sorry, I should have given a bit more context! In this case, it’s definitely the tubes. About one year ago there was an issue with the tube supplier’s test procedure, and they sent us tubes that seemed to fail early. We also do a burn-in test in the factory, but the tubes were good enough to mostly pass this test. So that’s the background. The date and symptoms of your PS-100 are entirely consistent with this being the issue. Regarding checking for any other potential damage, the rest of the circuit is protected by internal fuses which will be included once you request the parts.
You change tubes and fuses like this: