Thanks for your help and ideas. Yes I admit I was looking for the quick
fix. I'm going to need to remember my more in-depth troubleshooting
skills, limited as they are. (I worked as an electronics technician
about 20 years ago, used to do some component-level fixes of Macintosh
power supplies when I was working as a consultant, and have built small
projects). I do have a DVM and an oscilloscope, and 2 good units to
compare with. I wonder if I should invest in a capacitor checker. Kind
of makes sense that capacitors would be more likely to degrade than a
silicon chip or transistor. Would a resistor drift over time if there
were no current running through it? Yes, some of this is guesswork, but
it can be useful if in the exploration and exchange of ideas, I get
more of an idea where to focus once I get down to work.