"Larry Gagnon" wrote in message
...
I am attempting to repair a Midland Model 78-100 VHF Marine Radio for
a friend. I have basic radio electronics knowledge, some
troubleshooting skills, a 275MHz scope, VHF sig generator, freq
meter, RF power meter, a working VHF radio etc, but am unable to
locate the problem.

Symptoms a completely dead on receive and transmit on all channels,
but unit powers up good, all power supply circuits and voltages are
good, display and frequency display circuitry are good, no detectable
cold solder joints nor sal****er corrosion anywhere, power to all
chips is good.

I first suspected the PLL circuitry (due to its being common to RX and
TX), but signals coming out of the PLL, prescaler and VCO chips appear
ok.

Any suggestions as to where I might start looking would be greatly
appreciated.

Larry Gagnon VE7EA

IS the crystal in the PLL "ON FREQUENCY"? IF it is way off - but still
oscillating - due to some defect, that could cause the problem. The voltages
and such may "appear" ok, but the crystal won't allow "ON CHANNEL" signals
to come or go. Check your frequencies and such. The other thing common - is
some of the audio stages. Are they working? How about the function switches,
maybe not making full contact - especially if there is a radio/pa switch or
something similar. They could create similar problems. Those are the other
common things aside from the Power Supply legs. Microphone wiring is
sometimes common also, a broken wire or two, won't allow it to transmit OR
audio to come through to the speaker. I don't have any info on this radio to
be more precise.

Lots of luck.

DM