[Elecraft] Intermittent loss of power output K3

[John Saxon]

 Peter:
This is John Saxon, K5ENQ, in Pearland, TX, and I have experienced what appears to be the identical symptoms.  Also have contacted support, got some suggestions, tried them to no avail (mostly dealing with possible rf grounding issues).  Like you, it may operate perfectly for hours or days, then later I need to ATU and I get the same results as yours when yours fails.  My serial #3524.  Like you I am not inclined to send it in for fear it may not fail.  I also experience these somewhat intermittent failures when loading into a dummy load on my bench.

I am sorry I have nothing useful to convey, other than that you are not alone  :-)  

If anyone does come up with suggestions/solutions, please broadcast to group as there are now at least 2 folks with what appears to be the same issue(s).
Good luck to us all,JohnK5ENQ

    On Friday, March 1, 2019, 8:48:16 AM CST, Peter Lock <doc.lock at fast-mail.net> wrote:  
 
 Good day

Late last year, my K3 (no 6957) developed a fault.  The symptoms were:
1. No power output when keying the rig
2. TX LED on when keyed, (sidetone generated in CW mode)
3. Single bar showing on the RF power meter, whatever scale, ie 0 - 10 or 0
- 100
4. ATU tune command: relays clicking, TX LED on, no power output, no
indication on SWR meter; two horizontal dashes in the VFO A display area
where normally one would see the resolving SWR; in VFO B area 5.0W is
indicated
5. TX gain calibration failed on 5W and 50W;  mW TX calibration gain OK

I contacted Elecraft Support who suspected a failure of the LPA PA
transistor(s) and I shipped the rig to Watsonville where Q4 on the LPA board
was found to be dead.  Q4 and Q5 were replaced, re-biased and tested.

On getting the rig back, the same symptoms were present, but lasted only a
short while and the rig then performed normally, enough to have a couple of
QSOs, but then failed.  Since then the same symptoms have been present
intermittently.  I asked a friend who also has a K3 to try the rig to make
sure I was not doing something silly.  For about 20 minutes after switch on
the symptoms were present, then for no apparent reason the rig performed
normally for approximately 10 minutes before failing again.  We were testing
by repeatedly invoking ATU tune functions on different bands. Since then,
the rig will work or not work on switch on; it has worked flawlessly for
several hours but sometimes will present only the listed symptoms for
several hours after switch on.

When it is working, it all works, specifically the TX gain calibration
completes normally

After several days of performing normally, I relocated the rig to my
alternative operating location; it did not work, with the same symptoms.

Elecraft Support has been as exemplary as ever, but they are loth for me to
return the rig when it may well sit on the test bench being smug and
behaving normally.  It seems to me that the possibilities are  (i) a dry
solder joint (ii) a loose connection or (iii) a component on the verge of
failing.  I think I should next dismantle and reassemble the rig to try to
exclude option (ii), and perhaps find either (i) or (iii), although needle
and haystack comes to mind...  Has anyone suffered similar problems and
found a solution, or can someone advise where I should concentrate my
search?

Peter
M0RYB



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