[ICOM] IC-765 transmit audio problem

[Jack/W6NF]

Just in time for the SSB Sweepstakes (of course), and after not being 
used on SSB for a month or more, my '765 seems to have developed a 
transmit audio problem. To get any RF output with modulation the mic 
gain control must be turned up full resulting in only about 10 watts of 
RF output and almost no deflection of either ALC or compression meter 
positions. That amount of output requires almost hollering into the mic! 
With computer-generated audio being fed into the audio input port on the 
DIN connector on the rear apron the output power is normal. I have tried 
a second microphone with the same results.

I've seen similar symptoms in broadcast audio gear when electrolytic 
coupling capacitors age and dry out but since I have no service manual 
or schematic on this rig I don't know if that is possible in the '765. 
Has anyone seen similar symptoms and come to any diagnosis?

Thanks,

Jack, W6NF