[Elecraft] K2 VCO Problem

[Don Wilhelm]

Kurt,

A common cause for such temperature related behavior (won't work after it
gets warm) is a solder problem - usually referred to as a 'cold solder
joint'.  I would recommend re-soldering everything in the electrical
vicinity of the problem (refer to the schematic and make certain you hit all
the related components - some may be located away from the physical center
of attention).  In your case the components in question are all the ones on
the toop of the RF board schematic page 1.

Failing components usually produce temperature drift, but solder joint
failure is the most likely reason for a working/non-working problem.  Yes a
component CAN cause such a problem, but it is not as likely to do so.

73,
Don W3FPR

----- Original Message -----

Hi I am new to the list, but I am having a heat related problem with my K2
serial # 3511 when I added the KPA100. With With PA installed on the K2
case, and just used on receive  for several hours or so, if the K2 is
switched for the lower bands (160, 80, 40) to higher band 30m and above and
then returned to  40, 80, or 160, the VCO will not start up. You can return
to band higher than 40 m, and the VCO  will operate fine. This all happens
with a heat sink temp. of 23 degrees C, and if the K2 is  shut off the heat
sink temp must drop to at lest 21 degrees C for the VCO to start up again on
the 40, 80, 160 m bands.
With the PA removed from the K2 the VCO works fine. I am monitoring the VCO
voltage at R30 on the RF board when this happens.
This relates to a temp of only about 72 degrees F, and I have tried using a
heat gun to blow hot on the VCO area on the RF board with limited success in
producing the the same results. Have not found a way to raise the temp of
individual components yet.