Thanks @stereo5 and @wturkey. I figure it is something like that too. I’m hoping someone might chime in who knows where to look - I have no problem going in with a soldering iron, but I’m less confident at being able to spot the bad connection, and totally confused about why it’s affecting more than one light, but not at the same time. Guess I’ll have to take off the front panel and poke around. I do have a competent tech - unfortunately he’s got a 6 month backlog, but I do already have a vintage (‘73) Marshall tube amp on his waiting list, so maybe this is a good excuse to check in with him.
As for the tape suggestion, I’ll assume you’re joking or just misunderstood. I’m trying to get the backlights to stay ON, not cover them up. Either way, thank you for your folksy wisdom.
@boxcarman - the S-120 amp is 30 years old (and still fabulous), but I can’t rely on the owner’s manual for the current S-150.
Thanks!
Neil