In article , Ken Roser wrote:

Apparently there exists a problem with the HM56 microphone that causes
the radio to key up spontaneously due to capacitor failures on this
microphone.

Can anyone provide some assistance on the details of this procedure.
Supposedly there are 5 surface mount capacitors that need replacement.

Ken-

This is the first I've heard that someone had solved the problem, which is
apparently common. Mine keys the transmitter when power is first
applied. After several seconds, the transmitter unkeys and everything is
OK until powered down. Replacing the CMOS battery didn't help.

Somewhere I found a copy of the HM-56A diagram and parts list, possibly at
www.mods.dk. I suspected that a transistor connected to the CPU's reset
line was leaking and slowing down the power-on reset. I had not
considered capacitor leakage as a possible cause.

Please post if you learn more.

73,
Fred
K4DII