Strange SSB transmit fault on K2

[G4JQT]

Hello all.

Yesterday I noticed a tx fault on my K2 in LSB. When set to 15W, between pauses in speech, the RF rose to 5W and made sort of grinding noises when heard on a receiver. Talking reduced it, but in speech pauses it built up again over a couple of seconds.

SSBA set to 1 and SSBC 2-1, although changing these settings didn't seem to make any difference.

I switched to a dummy load which made no difference either, so not RF feedback I don't think. There was also what sounded like a one-second tick in the 'modulation' - from the real time clock perhaps?

Selected BAL on the menu, and re-adjusted R1 on the SSB board, but the erratic levels of RF (looking on a scope across 50 ohms) didn't really dip.

Switched to USB, and all ok! Got a nice dip on R1. Back to LSB, and all ok now!!

Anyone any ideas what was going on? Just used it on air and it's all fine again.

BTW, the earlier fault where I couldn't get anything out on SSB, and occasionally mic-through-speaker feedback was me just leaving the K2 in in BAL mode by accident!

Thanks,

Ian, G4JQT
     
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[Don Wilhelm-4]

Ian,

That "smells" of an intermittent carrier balance pot on the KSB2 board.  
When you rotated it, it started working,  I suspect it has nothing to do
with the LSB/USB selection, but simply 'went right' when you changed
sidebands.
You might want to obtain a replacement just in case it happens again.

73,
Don W3FPR

On 4/15/2013 5:26 AM, Ian Liston-Smith wrote:

> Hello all.
>
> Yesterday I noticed a tx fault on my K2 in LSB. When set to 15W, between pauses in speech, the RF rose to 5W and made sort of grinding noises when heard on a receiver. Talking reduced it, but in speech pauses it built up again over a couple of seconds.
>
> SSBA set to 1 and SSBC 2-1, although changing these settings didn't seem to make any difference.
>
> I switched to a dummy load which made no difference either, so not RF feedback I don't think. There was also what sounded like a one-second tick in the 'modulation' - from the real time clock perhaps?
>
> Selected BAL on the menu, and re-adjusted R1 on the SSB board, but the erratic levels of RF (looking on a scope across 50 ohms) didn't really dip.
>
> Switched to USB, and all ok! Got a nice dip on R1. Back to LSB, and all ok now!!
>
> Anyone any ideas what was going on? Just used it on air and it's all fine again.
>
> BTW, the earlier fault where I couldn't get anything out on SSB, and occasionally mic-through-speaker feedback was me just leaving the K2 in in BAL mode by accident!
>
> Thanks,
>
> Ian, G4JQT
>    
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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