[Elecraft] KPA100 Trouble

[John Sims]

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