The tuner has been ruled out as a cause to the problem. The K2 will show
the same behavior into a dummy load either with out without the internal tuner
installed. The radio itself did work for about a week with full (15W) output.
My best guess is the initial problem happened as a result of excessive
vibrations causing the ceramic coating to wear down enough to let RF pass
between relay K12 and C4 then to ground.
All inductors are ok visually and they show continuity (no open
conditions) with their respective areas of the circuit. I'm starting to
question the resistors such as R50 and R58(?) as being damaged in some way.
Usually a resistor will open with excessive current, possibly these are shorted
internally... They seemed fine with my DMM.
To clarify, If I set the power to 2W (even down to 0.2W) I will see the
correct value indicated on my external tuner (using the tune button). On the K2
display (and external tuner), after about 5 seconds or so, the wattage or
current (depending on the readout selected) will creep up building "speed"
until the "cal Cur" set-point is reached. At this point, the radio will remain
in a TX switched state without RF power output until I force it back into RX
with the "tune" button.
73, Damon
--- On Fri 02/08, Robie Elms < [EMAIL PROTECTED] > wrote:
From: Robie Elms [mailto: [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Date: Fri, 8 Feb 2008 10:28:39 -0600
Subject: Re: [Elecraft] K2 PA runaway current
Damon,<br><br>Since you say the current builds I believe you have a
spurious<br>oscillation. I would remove the KAT2 and configure the rig so
that<br>you can connect the output directly to a 50 ohm dummy load. This
will<br>eliminate the possibility of a tuner problem. If you still
experience<br>the same type of problem I would look closely at T3 and T2 to
make<br>shure they have the proper number of turns and are
connected<br>correctly. I would also look at RFC's 8, 9 and 10 to verfiy they
are<br>the correct value.<br><br>If removing the tuner eliminates the problem,
then I would first<br>verfiy winding and installation of T1 in the
tuner.<br><br><br>You will get more input from a number of individuals much
more<br>experienced with troubleshooting the K2 than I am on this e-mail
list.<br> However, perhaps my suggestions will get you moving forward
again.<br><br>Robie - AJ4F<br><br>On Feb 8, 2008 9:52 AM, Damon Wascom <[EMAIL
PROTECTED]> wrote:<br>><br>> Hello elecraft
list,<br>><br>> I need some help with troubleshooting my K2. I destroyed my
finals (twice) due to a shorted cap (C4) in the KAT2. For troubleshooting
purposes, the finals have been temporarily replaced with 2SC2078's ($0.68 vs.
$6-11 for the 2SC1969's). My problem is when I TX at any band and any power
setting the current starts to build until I get a Hi Cur warning.<br>><br>>
At this point i've: re-worked ALL solder joints on the RF board, performed
signal tracing per the manual, inspected every component visually, checked the
resistors and semiconductors in the TR switch and PA with my DMM (power off and
voltages during TX) and pulled out my remaining hair.<br>><br>> The same
problem happens with the 2SC1969's in place so the substitution of the finals
has been ruled out. I just don't want to fry any more (I can't tell my XYL
oops, I did it again...)<br>> She is already upset with me about
this.<br>><br>> Here is my K2 configuration:<br>> K2 #: 06351 (15W),
KNB2, KSB2, KAT2, KAF2, KIO2, K160RX, K60XV and KBT2.<br>> In other words,
"Fully Loaded".<br>><br>> I have been conducting tests with my MFJ-969's
dummy load. My belief is that the problem is in the PA but that's just a
guess.<br>><br>> Thanks, Damon KC5CQW<br>><br>><br>>
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