[Elecraft] Q11 Blown

[Don Wilhelm]

Richard,

Well, the loud pop was most likely one PA transistor exploding, so I 
expect you will have to replace Q7 and Q8 as well.  If you remove the 
heatsink, you will likely see one of the PA transistors damaged.
Yes, replace Q11 and Q13 together.
Get the K2PAKIT from Elecraft - that kit has matched PA transistors plus 
replacements for Q11 and Q13.
Just for good measure, order 2 1N5711 diodes - Elecraft p/n E560004.

Procedure: Remove Q7 and Q8, Q11 and Q13.
Install Q11 and Q13 first, then check the voltage at the base solder 
pads for Q7 and Q8.  It must be zero during receive.  Then do a TUNE and 
measure the PA transistor base solder pad voltage.  If it is not in the 
range of 0.60 to 0.64 volts, investigate the resistors in the Q11/Q13 
circuit.
Only after those checks should you install Q7 and Q8.

That should get the base K2 working.

Now it is time to try the KPA100 on it.  Get an external wattmeter and a 
dummy load for the test.  You are checking to see if you have good power 
control in the K2.  You can lay the KPA100 on its back on a box or book 
about half the height of the K2 for the test.  Connect the external 
wattmeter and dummy load, set the power knob at 50 watts and do a TUNE. 
What is the actual power?
If it is about 20 watts, all is fine, but if it is 100 watts or higher, 
you have a problem with the KPA100 wattmeter.
The most likely wattmeter problem is that D16 and D17 are damaged.

So what may have happened?  The KPA100 wattmeter diodes can be damaged 
by static from the antenna feedline.  When that happens, the K2 will 
still produce power, but the power output will be as much as the K2/100 
can deliver, often 180 watts.
If that situation goes unnoticed, the PA transistors in the base K2 are 
stressed and will eventually fail.  If they fail with collector to base 
leakage, Q11 and Q13 will also be damaged.
That is why I tell you to proceed in the steps I have outlined.

73,
Don W3FPR



73,
Don W3FPR

On 12/30/2016 5:38 AM, Dickie M0AUW wrote:
> Hi Don et all,
>
> My own stupid fault, I was tuning up my other transceiver and forgot the K2
> (fitted withK2/100) was still on and something went bang! On checking the K2
> there was no transmit, receive was ok. I traced the fault back and found
> that *Q11 had blown*.
>
>  I cannot visibly see any other fault but could you advise on other checks I
> may need to do or would this be the only likely fault from that sort of
> mistake. Do I replace Q13 as well as a precaution?
>