Thanks to Eldartford and Warnerwh. Have now replicated problem with amp disconected from system, so as you suspected, it is the amp itself. Simply being plugged in and turned on generates enough heat to trip the indicator. Placement is well-ventilated, so I doubt that's it. Will return to local techs, without much confidence. They must not have run it for very long! A trip to ADCOM, last I checked, was $140 + sh, more than the value of the piece warrants.
Thx again, John
Thx again, John