[Icom] ICOM HM-12 Microphone repair

[Jim Isbell]

A while back my ICOM 725 quit transmitting.  The receiver was fine, but 
no transmit.  At the time I had only CW and SSB capability.  I have 
since added AM and FM with the UI-7 module.  But when it quit I found 
that CW would put out a carrier but SSB didn't work at all.  It turned 
out to be a simple thing, the microphone was kaput.  After looking for a 
replacement and finding them in the $50 plus range I decided to fix it 
myself. At the local Radio Shack store I found a package that contained 
one condenser microphone element (RS#270-090) for $1.99.  It might not 
work, but for $1.99 it was a cheap fix.  I found that the element had 
just two leads instead of the three on the ICOM mike.  But I combined 
the power and the + audio lead together and tacked them to the + lead on 
the RS element.  The ground lead went to the - lead on the RS element. 
 The first test showed that I was not getting full modulation so I went 
back in and moved the power lead from the 1K resistor in series with the 
power  to the other end of the resistor where there was already a hole 
in the circuit board.  This removed the 1k resistor from the circuit and 
fed the power directly to the mike.  That solved the problem.  I am back 
on the air at a cost of $1.99 plus tax.