[Elecraft] K3 audio input went away.

[Ron Fial]

My K3 rear panel Mike input signal input suddenly went away. It had worked fine for several years.    I key the PTT and speak but no indication of audio input.  The K3 receives normally on main and sub rcvrs.   It can transmit SSB fine using the stored audio buttons.  Tune control works. Auto tuner works. Everything else is normal.  

My  K3 audio input is from a Plantronics mike to the Mic jack in the REAR panel.  In the menu or config,  rear panel Mic input is selected including the FET Bias.  Front panel mike volume pot is set OK, usually at 12.  The Plantronics Microphone tests fine on other equipment that has bias voltage, nice audio output at normal levels.  

Before this happened, I was adjusting some other menu settings.  I don't currently have a mike for the front panel, so can't test that input yet.  (Need to order a new MH2 from Elecraft, no other Kenwood mike available at the moment.).  I cannot figure out what I did to make the rear Mic audio input stop working.  Think its unlikely a transistor or op-amp just decided to die.   Suspect I accidentally changed something in the menu or config system.  Before I start taking things apart and hook up the o'scope and spend gobs of time with the schematics, does anyone have any suggestions for what menu disaster I may have caused?

(I recall that Menu and Config has bitten me before)

73, Ron. KO7V