Time for a hot air gun (hair dryer will do) and some freeze mist. Open
up the radio, heat up the transmitter section with the hot air gun while
transmitting into a dummy load. When power disappears, cool it a section
at a time. Then if that doesn't isolate it, heat it a quarter at a time,
and cool parts of that to find when it comes back. It can be a bad
solder connection (probably missing solder completely) or inside a part,
likely a signal or power circuit going open which can be inside a
transistor or IC. It can be ANYWHERE in the transmitter from the
microphone connector to the coax connector including the local
oscillator injection strings. If it was in the audio, it probably would
show having an tinny sound, e.g. bass tones weaker than treble because I
think its working with a tiny coupling capacitor effectively in that bad
connection. In Kenwood its usually some connecting cable not making good
contact to the posts and often cured for a while by removing and
replacing the cables.
73, Jerry, K0CQ
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