[Elecraft] K2 run-away current

[Don Wilhelm]

Damon,

Sorry to hear of your problem.

The heating of Q6 sounds like either Q5 or Q6 may be 'taking off' and 
oscillating on its own - I have never seen that happen, but your 
symptoms certainly sound like that is a possibility.

If you can transmit to a dummy load and listen to the signal on a 
separate receiver, that may be revealing.  If the signal sounds 'fuzzy' 
or changes to a different frequency, that would indicate some kind of 
self oscillation.

You should check C118, C116,  C121, C120, C122, R48 and R49 and RFC6 for 
proper values and good soldering.  Measure the resistance from Q6 
emitter to ground to be certain it is 1.5 ohms.

I know those are just starting points, but worthy of checking.

KC5CQW wrote:
>       After a rather long TS session with Gary S., we both agree that there
> is a problem in my PA section. 
> What I have noticed is the current will start to build rapidly and Q6 gets
> really hot. When the HiCur warning displays (at any power setting above 1W),
> the RF power drops to zero and the K2 remains in the TX state. The K2 then
> displays about 3A power draw and holds until I actuate the tune button
> again. I have the Cal Cur set for 3.5A. At this point the K2 is configured
> in a basic QRP/CW state. None of the options are installed for TS purposes. 
>
> The BPF and LPF are fully functional. RX mode works great.
> As a precaution, I have reworked/replaced:
>
> All solder joints on the RF and control boards, 
> Re-wound T1-T4, 
> changed Q11, Q13, Q7 and Q8, 
> several resistors in the PA section, 
> Q8 on the control board, 
> RFC4 and RFC5, 
> C125, C126 and C137
>
> None of these are related to the problem (It didn't improve; waste of time
> and money...)
>
>      I performed a full signal trace routine and DC voltage checks points on
> the RF board per the manual.
> Summary: Something is demanding allot of current in the PA until the CalCur
> set-point is reached. At this point it stops the RF power and the current
> draw "floats" near 3A until I return to RX mode.
> I really want to get back on the air!!! 
>
> 73, Damon KC5CQW
> K2 #: 6351 (50 hours to build and 100+ to troubleshoot!)
>