[Elecraft] Intermittent loss of power output K3

[Leroy Buller]

Look at the two diodes in the SWR/watt meter circuit.  These two diode are
critical to the operation of the K3.  These are the foundation of the K3s
ALC implementation.  Ive had to replace them.

Lee K0WA

On Fri, Mar 1, 2019, 8:47 AM 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
>
>
>
> --
> Sent from: http://elecraft.365791.n2.nabble.com/
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