Tried hooking it up to the cable box, and hmmm....no audio.
Speaker wasn't blown and the output tranformer seems fine, so the circuit must not be getting powered. Sure enough, 5 minutes of poking around revealed that a 470-ohm power resistor feeding the audio output tranformer had opened up. I don't have a replacement in this value, so I'll have to order one or something. I'm sure that once it's replaced, audio will come back to life.
