Thanks, Dave, it's not the 10ohm resistor nor the 100ohm resistor. But I did notice the brown-red-red resistor connected to pin 1 of V10 is loose. Still touching but needs resoldering. Off topic, I noticed that while removing the chassis bottom, I was testing for continuity on the speaker posts. What surprised me is that both the common (-) and positive (+) speaker posts have continuity when the SELECTOR on the front of the 500-C is selecting those speaker posts. For example, if the SELECTOR switch selects SPEAKER 1, the posts on the back of the unit for both + and - SPEAKER 1 posts have continuity. That means that both + and - are connected to ground which is unconventional and I thought a short circuit. The posts for the other speakers (SPEAKER 2) do NOT have continuity in this example which is what I would expect if I had selected SPEAKER 2. Can anyone explain this phenomenon?