[Elecraft] K2/100 refurbishment

[Michael Carter]

Hi Steve,

No answer for your question #2 - Elecraft sells
packs of 25 screws for modest price, but shipping
to U.K. and VAT (if applicable) may dictate
otherwise.  Maybe pose that question to John,
G3PQA - he's done a lot of work on Elecraft
radios for fellow hams in the U.K.

Before doing any tests on the PA module
itself, go into the K2 secondary menu
(tap Menu, then tap Display) and find
the PA entry - it should be 'on' - you can
also check the PA fan control for proper
functioning.

If the 100 watt PA is enabled and the
problem persists,  then the
detective work ensues.

On question #1: carefully remove the KPA100
100 watt PA module from the base K2/10.
There is an internal RF feed from the base K2
to the KPA100, a speaker cable, a 12 V DC power
cable, and a ribbon cable to the Control panel.
The small plugs are 2-pin plastic with non-locking tabs, and
are easy to remove.  Be careful to label the two
identical plugs for RF and 12 VDC feed - you
don't want to swap these upon reassembly.
You can lay the KPA100 alongside the K2 and keep it connected
for powered troubleshooting - use a couple
of books to raise the KPA100 up to the level
of the K2 side panel.

I would first check (with power supply off and
disconnected) the resistance between
the PowerPole terminals on the KPA100.
If it's low, then you could have a shorted
PA transistor (Q1 or Q2).  There are additional
resistance checks described in a table
on p. 45 of the KPA100 manual - see the
Support menu on the Elecraft web page
for access to manuals - the KPA100 manual
appears under the Classic Line link for
K2-related manuals.  Those checks require
removal of the KPA100 module, hence my
recommendation to pull it.  You could do
the PowerPole resistance check before
removing the PA module, of course.

If there's no PA transistor short, then
there may be a problem in the diode
T/R switch.  This would take a bit more
effort to test, so I would hold off until
you've done the other resistance checks.
Some radios have been damaged by
lightning-induced overvoltages
on the cables, and the T/R switch
diodes have been mentioned in older
posts.

Given what you observed about
case screws being corroded, I would
unplug and plug those internal cables
and inspect for corrosion when plugs
are separated from their mates.

73,
Mike, K8CN