[Collins] KWM-380 +14v wiring error?

[Dan Frank]

Hi All,

Today I was debugging a problem with my KWM-380, which I traced to a blown
fuse (F2) on the power supply control board.  According to the service
manual, this fuse is in the +14v Audio PA/Oven circuit.  This was a big
surprise, since the audio was still working, but I couldn�t find any +14 to
the RF circuits on the receiver/exciter board.  Upon ringing out the
circuits with an ohmmeter, I discovered that indeed the connections seemed
to be reversed at the power supply control board.

According to the schematic, the Audio/oven +14 goes to pad 12 on the power
supply card, while the regular +14 goes to pin 10.  The regular +14 goes
through a 1.5 ohm series resistor and there is a 330 uf capacitor to ground,
while the audio/oven +14 comes directly off the regulator circuit.  There is
a yellow wire soldered to pad 12, going to pin 14 on the plug at the
receiver/exciter board.  An orange wire connects pin 10 to pin 13 of the
plug.

Either there was a manufacturing error at Collins and these wires are
reversed, or the schematic is in error, and the series resistor and
capacitor to ground should be on the audio/oven circuit.  Does anyone know
what the right answer is here, or could someone with a KWM-380 take a peek
and see what color the wires are to pads 10 and 12 on the power supply card?
The radio actually works like this � it has for many years � but I wonder
whether I should be operating it in this configuration.  (Of course I also
wonder why the fuse blew, and if this is related.)

By the way, as far as I know this radio was only serviced by Collins.  It
had most of the service bulletins installed at the factory in May 1982.  The
receiver/exciter board is Rev K.

Thanks in advance for any insight you can offer.

   73,

     Dan Frank
     W9NK


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