The Curious Case of the Missing RF

[Kevin Rock]

Good Day,
    This weekend, as the twenty meter segment of the Elecraft CW Net was getting under way, my K2/100 went a little crazy.  After sending for about one minute the relays started chattering, the keyer response was in no way related to paddle input, and upon later reports my signal went from a fine tone to a hiss.  During the short time of reliable sending I responded to Tom's (N0SS) kind offer to take the net with a series of Cs and went QRT.  I was forced to use a lesser rig :( to run the 40 meter net.  My Icom 706 is not the best at full QSK with its relays clacking in my ear and the sidetone fixed to the AF Gain level.  The filter in no way resembles the response I get with my K2's filter choices.  
    In between nets I pulled the amplifier off and found the culprit.  Here is where we segue back so put on a good Jim Reeves album or one by my favorite: Marty Robbins.  This is the time for a good ballad telling the tale of missteps in one's life.  Set the dial on Professor Peabody's Way Back machine to the recent QRP to the Field and the place to Bald Mountain State Park.  N7NLU and I are working the contest with our Elecraft rigs.  He, of course, is doing much better than I but we both had fun until the downpour told us to pack up our things.  As I drove back toward Banks the winds were so strong they were slowing my F250 significantly.  The downpour was making visibility quite poor.  But both the gear and I returned home safely.
    As I was drying myself by the fire and talking with Sam (the cat) I started rewinding the antennas in the correct disposition and unpacking the hastily stowed gear.  Wandering into the shack I sat and found the screwdriver to replace the original top with its ATU with the amplifier top.  Here is where the story may provide clues so stay awake :)  I found a couple of text books and set them under the inverted amplifier.  Then I proceeded to poke plug A onto pin B all the way from the front to the back of the rig.  Since dinner was next on the agenda the inspection faze of the rebuild was cursory at best.  WARNING: don't do this at your shack!!  And so on to dinner.
    The next day's nets and those the week after went well.  I got and gave good reports across the continent.  Well as good as could be expected under Spring storm conditions.  This brings us to Sunday the 28th and the commencement of the twenty meter net.  Since I've already related that part of the tale I'll not bore you with a coda.  I will jump to the problem staring me in the face when I inspected the AUX RF connection to the main RF board.  The inner wire of the coax's part of the plug had been pushed out of its normally seated state.  For the last few weeks I had been running in a potentially intermittent state.  I reseated the wire with its little brass thingie into the plug.  This did not solve my problem.  In fact I had lost all RF output from the amplifier.  At this point I could still hear with the rig.  Later I lost hearing as well.  
    On Monday I went to see Ron D'Eau Claire in Forest Grove.  We chatted for a while and I mentioned the sad state of my K2/100.  He aimed me at further tests and asked for a follow up email.  After all of my errands were done I walked through his measurements.  The finals were still alive to my surprise.  I had not smoked them as I had feared.  (This would not explain the deafness of my rig however.)  Further tests were necessary.  I pulled the AUX RF plug and the power to the amp.  Found a BNC to SO-239 adapter, a gel cell, and the barrel connector for the K2.  Most of this was still in my gear from the QRPTTF expedition.  The rig worked.  It could hear and it could transmit.  But, when I replaced the amplifier top's connections and ran the antenna through the SO-239 on the amp it was deaf and dumb even at low power.   Hmmm... curious.  Emails to Ron and Don, W3FPR, provided me with a few more steps.  I took some of the readings but in checking the RF AUX connection for the umpteenth time I worried the shield connection to the point of failure.  
   At this point I decided it was better to get some rest before proceeding.  Since the next day was a work day I was unable to complete the tests or repairs for quite some time.  Not a good day at the office while one is worried about their K2!  When I got home I had three projects: repair the OS on my computer, troubleshoot some electronics for work, and fix my K2.  Each of these was done in turn or simultaneously.  Since I had about thirty feet of RG-174 lying around I cut a new cable.  I did not have either the time nor the desire to pull the amp PCB off so I undid the connections from the part side and surface soldered the shield.  The inner wire connection wicked clean so  I was able to mount that through hole.  The brass parts in the Molex connecter were another story.  I did not want to risk deforming them into uselessness so I soldered the coax lead on top of the crimp.  I bent the connections out to increase the spring tension and plugged it back to the RF board.  
    Time for a test.  I pressed the go-start button starting off with very low power and was pleased to see the needles on my MFJ tuner bounce feebly.  I turned up to just shy of the amplifier turn on position and repeated the test.  My SWR was a bit off into my dummy load so I retuned.  Turned the power up to fifty watts and was greeted by the relay clicking and the needles bouncing more vigorously.  Problem solved with a temporary fix.  ECN will run from my precious K2/100 again!
    Moral of the story?  Don't mix allusions with metaphors.  No, different story ;)  Make sure to inspect your connections closely and carefully after a QRP field trip involving top swapping.  Don't let dinner take time away from electronics!
   73,
       Kevin.   KD5ONS

PS.  Thanks to AC7AC, W3FPR, and N7NLU.  Karl, you were right, it was a simple fix.
    KJR
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[Ron D'Eau Claire-2]

Good to hear you found the problem, Kevin!

I remove the K2 side panel nearest the connectors when I replace my KPA100.
That way I can make sure the cables are properly positioned in the cutout in
the shield and properly plugged in AFTER the KPA100 is screwed in place.
Then I replace the side panel.

Ron AC7AC

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