[Elecraft] K2 -- loss of output power control

[Don Wilhelm]

Brian,

The real mystery is that this initially occurred when you removed the 
KPA100 to tighten the PA transistor screws.  I really would not think 
that would trigger a component failure, so I encourage you strongly to 
look for a bad solder connection.
Be certain the wire from the center of the SO239 to hole 6 of the T4 
connections is in place and well soldered - that one is easily 
overlooked.  Do the rest of the T4 connections look 'like mountains, but 
not volcanoes'?  Re-strip if they have that volcano appearance.
You might also check R28 and R29 too.  A bad capacitor is a difficult 
thing to find - fortunately they are not encountered often, but check 
anyway.

Measure the resistance from the wiper of R26 to ground - it should be 
close to 43k.
A possibility is that R26 itself was ready to fail - it perhaps worked 
until it was touched.

You could possibly use some other diode at D16 and D17, but I don't know 
the response characteristics vs. frequency.  The 1N4148s will work fine 
down to about the 2 watt level, I don't know how low you wish to have 
accurate power control and indication.  Elecraft will likely send you 
1N5711s if you can't find them locally.

73,
Don W3FPR