This file describes a very difficult to find fault which could
occur on many rigs, and so is of general interest.

    I recently acquired an ICOM IC-255. It worked fine in the shack
 and was OK for several hours mobile. Then, with no warning, no TX
at all. Symptoms: OK on RX, no transmit power at all on either high
or
low power. There is a problem on these rigs of a resistor which overheats
in the power control circuitry, but this showed OK.

    Apparent fault was PA module; an expensive item if available.
   Some probing around with a voltmeter in the power control circuitry
showed inconsistent voltages; they seemed to wander, i.e. from
a high sorce impedance (I was using a digital high impedance meter)
On the resistance range, with power off of course, I tried connections
to the supply current senseing resistor. This was it! A dry joint ,
which appearred somewhat intermittent, caused the sense resistor to
appear O/C to the power control circuit. Cause; years, amps, mobile
miles!
  Resolder, reassemble, no cost, all OK and full O/P power again.

   It seems to me that this is a likely problem in many rigs, so don't
rush to buy a new PA module unless you arer sure!!!