[Elecraft] KPA500 Problem

[Joe Hutchens]

Did you find your problem?  Any fault codes?

I suggest contacting support at elecraft.com, but if were me, I'd check all 
internal connections first and do a quick visual.  I suspect a problem 
with the elaborate TR switching circuit or something that controls it.

I see a couple 51 ohm resistors on the schematic at the input to the PA 
module, so if the TR switch was working, I would NOT expect hi reflected 
power to the rig with no power out of the AMP.

Joe Hutchens  ( AJ8MH )
http://webpages.charter.net/aj8mh-radio/


On Fri, Sep 21, 2012 at 8:01 PM, Phillip Shepard wrote:

> I put my new KPA500 (s/n 1057) together earlier this week and have 
> been
> loving it, although it has seen only light use so far.
>
> However, that changed this afternoon.  I used it briefly on 40m LSB a 
> few
> hours ago and all was fine.  About 35w of drive for 550w out.  I just
> retuned the antenna to the low end of the band, yielding a 1.0:1 SWR 
> at the
> K3 in the standby mode of the KPA500.  When I switched the amp to 
> operate
> and keyed the transmitter (tune control), the amp power LEDs jumped up 
> to
> about 500w and then went to 0.  Subsequent keying  show a very high 
> SWR at
> the K3 (65 to 99:1) and the K3 puts out no power as does the KPA500. 
> I
> tried a dummy load with the same result.  If the amp is in standby 
> mode the
> K3 acts right and the power and SWR LEDs on the KPA500 act right (100w 
> out
> at a low SWR).  Putting the amp into operate mode acts like the input 
> SWR is
> very high.
>
> I tried tightening up the cables at both ends (BTW, I am using the 
> control
> cable between the rig and amp for maximum integration, and the K3 
> knows to
> reduce the power out when the amp is in operate).
>
> I hope I am doing something wrong, and the fix is simple.  Any 
> suggestions
> of where to begin?  Thank you.
>
> 73,
> Phil, NS7P
>
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