KPA100 Trouble

[John Sims-2]

Fellow Elecrafters--

This morning I tested a few things with my "dead" K2/100.

K2/100 configuration:  no response at power-on, power supplied via
KPA100 J3.  KPA100 heat sink warms.  All power pole connections
checked.  13.9V from the Samlex 1223 power supply.  2V or so detected
were detected at the interior J3 leads.

Basic K2 test:  all functions are normal, receive and transmit, all menu
items are normal. E = 13.6, i = .38.  All internal accessories work
(160m, SSB, noise blanker).

K2 with KPA100 connected, power supplied through K2 J3:  rig turns on,
all functions are normal.  KPA100 fan runs for a minute or so.  Normal
receive and QRP transmit, internal SWR bridge works.  All primary and
secondary menu items appear normal.  PA "E" message is normal, "12."  E
= 13.6, i = .38.

No scorching or shorts detected.  I'll only remove the KPA100 heat sink
if I have to, but no visible signs of a problem after exploring
underneath it with a miniature LED.  The KPA100 has been in use for a
little more than a year without problems.

The trouble began yesterday afternoon as I was testing a receive
antenna.  I switched power supplies from my regular Samlex to a
regulated supply I've used with the K2/100 in the past.  All connections
were carefully checked.  One thing I failed to check was the power
supply output -- it worked the last time I used it so I didn't bother
(an important lesson learned).

I've checked the regulated power supply output voltage after the KPA100
failure and it's only 1 - 2 volts.  Something happened somewhere.

All was well with the regulated-supply K2/100 as I checked out a receive
antenna for about 30 minutes.  I never transmitted while the regulated
supply was connected.  I turned the rig off while working on an outdoor
antenna.  When I returned to the shack, the rig wouldn't turn on and I
noticed the heat sink was slightly warm.

Here's where I am:  the basic K2 checks out fine.  Some functions of the
KPA100 work when it's attached to the basic K2 (fan, SWR meter).  No
visible damage is apparent inside the KPA100.

I don't have a clue where to start.  My K2/100 technical skills have
diminished in the time since I completed the rig.  I'll have a chance to
work on the rig again this evening.

Any suggestions where to start would be appreciated.  Are there any
specific component failures I should look for after a problem somewhere
in the DC input path caused by a faulty power supply?

73,

John, N7ON  K2/100 #5023
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