/diy/ - Do It Yourself

I started this thread over at /g/ but no one has any ideas.

I've got these powered speakers which have an analog amplifier circuit inside. When I lower input volume and raise it slowly sound cuts out and then past a certain threshold I hear a pop and sound comes back in. I popped them open and couldn't see any swollen caps or burn out resistors. I'm a noob to this stuff, where should I start with diagnosing this thing? I'm guessing I'd need an oscilloscope to probe the signal on the board to see where it's going dead?