Q11 Blown

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Q11 Blown

Dickie M0AUW
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?

Thanks in advance.
Richard M0AUW
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Re: 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?
>
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Re: Q11 Blown

Dickie M0AUW
Excellent Don,

Many thanks for your quick response, I'll start as soon as I can.
Happy new year and 73s

Richard M0AUW
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Re: Q11 Blown

Don Wilhelm
Richard,

If you do not have good de-soldering tools, be careful when removing
components.  There is no sense in removing the component intact.  The
board is more valuable than any component.
Cut off the leads close to the component body (or crush the component
with pliers if necessary so you can remove the leads one at a time.
Clean up the excess solder with solder wick and if solder still remains
in the holes, heat the solder pad and push the solder out with a wooden
toothpick.

Happy New Year to everyone.

73,
Don W3FPR

On 12/30/2016 8:49 AM, Dickie M0AUW wrote:

> Excellent Don,
>
> Many thanks for your quick response, I'll start as soon as I can.
> Happy new year and 73s
>
> Richard M0AUW
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/Q11-Blown-tp7625179p7625183.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
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>
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> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>
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Re: Q11 Blown

Dickie M0AUW
Just completed the work, as usual you were spot on, Q11 and one of the PA transistors blown.
Couldn't see that the transistor was damaged until it was removed. Fitted the PA kit and did all the checks, all working back to normal.
Much appreciated Don.

Best 73s Richard
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