Prompted by the condolences on the death of my Beckman DM73 Circuitmate, I brought the carcass back to Squidwrench, took it apart, annoyed the switches, and re-soldered the battery connections:
I worked minute dots of Caig DeoxIT into the switches, without disassembling them, with magical thinking guiding my technique. One of the battery connections seemed suspect, but we’ll never know.
In any event, it beeps happily when turned on (*), the LCD behaves properly, it’s no longer pressure-sensitive, and life is good! It surely needs calibration, but that’s definitely in the nature of fine tuning.
Thanks for nudging me into Doing The Right Thing™.
(*) Including the double beep with the AC/DC button held down.