[Elecraft] Intermittent loss of power output K3

[Peter Lock]

Thank you, Keith.
It was indeed a poor solder joint on one end of D1 on the LPA board; there
was a hairline gap between the solder and the terminal of the diode.
Reflowing the solder has cured the problem.
Peter
M0RYB

Hi Peter;
It definitely had one bad FET on the LPA when it was here, I do not see 
in the report that it was intermittent, so I may not have looked closely 
for those types of failures.
If you are sure it makes MW power when it is in the failure state, then 
it is highly likely the LPA.
Inspect D1 closely, I have seen one side have poor solder, or it can 
heat and the solder crystallize. Re-flow solder.
Pull the KPA3 but leave the KPAIO3 riser board and you can run it with 
just the LPA.
Disregard errors about KPA3 or set it to "not inst" while you are 
working on it.
Then set for several watts (not 5 exactly) and long press XMIT to go 
into TUNE, IE transmit a carrier. (TUN PWR must be at "nor").
Then take a stick and tap around on the LPA. Around D1. Also the 
green/red enamel on T1 & 2 can fail and the windings can short.
Tap the three bias pots, sometimes they fail internally, or their solder 
points.
Look at all parts for solder problems.
You can put it in the fridge and chill it down to encourage failure, or 
leave it on for an hour with a blanket over it to heat it up.
Keith WE6R