[Elecraft] K3S - No high power output - Low power OK

[Ben Gelb]

Hi Ken -

I had a similar issue with my K3S in May (SN 11272 - very similar age).

I detailed it in this thread:
http://mailman.qth.net/pipermail/elecraft/2020-May/275684.html

It ended up that R5 on the KPA3A board (part of QSK T/R switching
circuit) had a broken solder connection due to the fact that the
component does not match the footprint mechanically on the PCB, and so
a solid connection is basically impossible (Elecraft confirmed this
was a problem with Rev D of the KPA3A, which I have, and that it was
corrected in Rev E). I was able to fix it by moving the component
slightly to borrow some PCB copper from an adjacent component.

In my case I found that the problem affected transmit (as you
describe) but also receive. If I dialed the power knob up and down
across the low/high power threshold while listening on a busy band,
I'd hear all the noise go quiet when I moved to high power and the PA
switched in. It was also intermittent, at least initially - I guess
thermal heating/cooling made the bad connection go in and out. So this
may be a good debugging step to try to determine if it is the same
problem.

Good luck debugging your issue. I will be interested to learn if it is
the same problem.

73,
Ben

On Mon, Jun 15, 2020 at 8:30 AM Ken Bolin <ken.bolin at snet.net> wrote:
>
> My K3S is about 3 years old and is S/N 11185. It has operated flawlessly
> since it got out of the box.
>
>
>
> I was using it this weekend in the VHF contest and operated perfectly until
> Sunday afternoon. I took a break for dinner and came back about two hours
> later and found that I had no power output. The radio was left on during
> that time. There was no indication that there was a power surge of any kind
> and there was no smell of anything electrical. Since I wasn't transmitting
> during that time, there was no SWR issue.
>
>
>
> After doing some initial troubleshooting, I found that the rig worked
> perfectly at low power but when I go above 9 watts (12 watts on HF) I get no
> output. The display indicates two dashes where the SWR is displayed and the
> power indicates 0.0 W.  When I try to transmit with higher power, the red TX
> light comes on steady and the K3S also keys my amplifier properly. I've
> tried it on several bands with the same results.
>
>
>
> The only other thing of interest is that when I came back to the rig after
> dinner, the rig tried to transmit in CW while receiving in TX Data. I did
> not leave it in that configuration. That may indicate that something my have
> happened with the S/W settings.
>
>
>
> Any suggestions of where to start looking
>
>
>
> Thanks
>
> Ken W1NG
>
> w1ng at snet.net
>
>
>
>
>
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