Oops K1 Dead!

[AF6NI]

I am not the builder of the K1, so I am not familiar with the circuit. I do have the original manual however.
This morning I  was testing an antenna and I think I let the SWR get too high. Result - the K1 is now completely dead and it appears as if my 12V supply has a dead short across it when I try to power up the K1.
Any suggestions on where to start looking is gratefully appreciated.
Thanks and 73,
Joe

[Don Wilhelm-4]

  Joe,

Assuming you were correct that the K1 failed due to a high SWR on the
antenna, then the most likely component to fail is diode D19.
Try lifting one end of D19 and operate the K1 into a dummy load to see
if it still works OK.  If so, replace the zener diode.

That diode is there specifically to break into conduction in the
presence of excessive RF voltage (caused by a high SWR).  Sometimes it
just breaks over and does not fail, but in extreme cases, it sacrifices
itself to save the rest of the K1.

73,
Don W3FPR

On 4/8/2011 11:07 AM, af6ni wrote:
> I am not the builder of the K1, so I am not familiar with the circuit. I do
> have the original manual however.
> This morning I  was testing an antenna and I think I let the SWR get too
> high. Result - the K1 is now completely dead and it appears as if my 12V
> supply has a dead short across it when I try to power up the K1.
> Any suggestions on where to start looking is gratefully appreciated.
> Thanks and 73,
> Joe
>
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[AF6NI]

Don, thanks for the info. I just lifted one end of D19 from the board and indeed it is a dead short. I powered up the K1 without the band module installed and it powered up fine, so that indeed is the problem.

Since I am so D&*&n stupid, I don't think I'll use the K1 without the Zener installed. It looks like changing out Q7 would be a MUCH bigger deal, so now I'll go on the hunt for a 1n4753 locally -- maybe at RF Parts in San Marcos.

Thanks again.
Joe
AF6NI

PS  - boy it's nice to have a radio that can be worked on. I also use many "boatanchors" and that's one of the advantages to them also.