Thanks so much for the detail, cjpremierfour. That sort of checklist sounds very helpful -- especially checking the tweeters. I'm aware that low-frequency, powerful current can damage them so I'll be careful.

I'm pretty concerned about getting a good look at the crossover -- I simply do not see how one might remove the crossover for repairs so I expect this must all be done with the crossover still mounted inside the cabinet.

Can anyone recommend any fundamental test on the various components (capacitors, inductor, etc.) for someone without an oscilloscope or any fancy gear? That schematic looks brutally simple and I can tell an inductor from a capacitor from a pot.

I have this sneaking suspicion there's a wire loose or something and would like to be able to check all the circuit connections.