K2 Lo p on 10 12m when its cold outside.

[EMD]

I have had my K2 (7109) for 3 years now and I have noticed something about it when it gets cold out.  Every year when the temperature falls I lose 10 and 12 meter capability.  I have read the posts on this forum with little success in resolving this issue.  My K2 sits next to an upstairs window, I have to admit I have been a little lax in getting the window properly enclosed since I use a MFJ window adapter for my antenna.  This morning was particularly cold and when I touched my radio it was very cold.  After turning it on it was once again dead on 10 and 12m.  I decided to see if warming it up would help.  I got my wife's hair dryer and blew some hot air on it and after about 5 minutes 10 and 12m are back.  I had it on 10m dead and then it came back as if I had just turned it on.  So this makes me wonder if I have a bad solder joint somewhere in the tuner?  

Any help/ideas are always greatly appreciated.

Ed K3ENV

[Don Wilhelm-4]

Ed,

Yes, it could be in the tuner - set the tuner menu to CALP and see if it
still happens.
CALP bypasses all the L/C elements, so if the problem is in the tuner
L/C section, it will be bypassed.  If the problem were in the tuner
wattmeter or thru path, all bands would be affected, so you already know
that is not it.

More than likely, the problem is in the low pass filter, and yes I would
expect a solder problem or an inadequately stripped and tinned toroid.  
If you have the KPA100, there is one LPF in the base K2 and yet another
in the KPA100.

There is also the chance that the problem is in the bandpass filter.

You might try putting it in the refrigerator overnight to induce the
failure -remove the top cover so you can direct the heated air at one
particular spot - you my have to fabricate a narrow nozzle for the hair
dryer.

73,
Don W3FPR

On 11/18/2014 1:22 PM, EMD wrote:

> I have had my K2 (7109) for 3 years now and I have noticed something about it
> when it gets cold out.  Every year when the temperature falls I lose 10 and
> 12 meter capability.  I have read the posts on this forum with little
> success in resolving this issue.  My K2 sits next to an upstairs window, I
> have to admit I have been a little lax in getting the window properly
> enclosed since I use a MFJ window adapter for my antenna.  This morning was
> particularly cold and when I touched my radio it was very cold.  After
> turning it on it was once again dead on 10 and 12m.  I decided to see if
> warming it up would help.  I got my wife's hair dryer and blew some hot air
> on it and after about 5 minutes 10 and 12m are back.  I had it on 10m dead
> and then it came back as if I had just turned it on.  So this makes me
> wonder if I have a bad solder joint somewhere in the tuner?
>
>

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[EMD]

Hello Don,

Thanks for your reply.  After setting the ATU to CALP 10 and 12m are still dead, the other bands are fine.  I do not have the 100W option installed.

Ed

[Don Wilhelm-4]

Ed,

Since those easy steps did not reveal the problem, you will have to
resort to some Transmit Signal Tracing to find the problem.
Use the stage-by-stage points shown in the manual Appendix A page 14
starting at the middle of the left column.
BUT you will have to deviate from the instruction to set the K2 on the
40 meter band - use a failing band instead.
If the measured RF voltage is greater than the expected value, that is
OK.  What you are looking for is the 1st stage in the sequence where the
RF voltage is significantly *less* than the expected value.  That is the
output of the failing stage.

73,
Don W3FPR

On 11/28/2014 10:50 PM, EMD wrote:
> Hello Don,
>
> Thanks for your reply.  After setting the ATU to CALP 10 and 12m are still
> dead, the other bands are fine.  I do not have the 100W option installed.
>
> Ed
>
>

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