(posted by K0CQ)

Chasing the schematics, I find the meter is driven by the S-meter circuits for SSB and FM through diodes for all positions of the meter switch. The difference is that its also driven by a op amp on the 9 MHz Mixer/IF board 81594 with a series cal pot and a diode. There's also a shunt capacitor. If the cal pot got turned way up it might take over, if the op amp failed or a board ground failed, or something failed in the ALC FWD detector circuit to push lots of voltage to the op amp (U1A) that would drive the meter full scale and beyond all the time. I didn't chase down the FWD power detector circuit, but I think its also used for ALC and I recall reports of Tentecs sometimes losing diodes in that circuit from nearby lightning while connected to an antenna.