Velodyne HGS-18 BG repair attempt

Customer states that there is (was?) a hum, then "intermittent" (hum or actual output?), and now dead (presume no audio output at all?)
Preliminary testing indicates that there is a hum when powered up, albeit a bit delayed.
After taking this video, I disconnected the red/black twisted pair audio feed at the top (servo) control board, and touched the input pins on the connector on the PCB, and heard this HUGE blap, and then nothing - then came the burnt smell. I blew up the little 8 Ohm Kenwood SP-430 communications speaker.
Note to self: next time do something to mitigate such large amplitude excursions at the speaker output when messing with seemingly high-gain audio input circuitry.
Maybe some resistors in series with the next (currently non-existent) test speaker. Or a power resistor(s) on the speaker output, and a scope across it/them.