KPA100 high output, again

[Jeff Kinzli N6GQ]

Greetings Elecrafters,

K2 #5945 with KPA100 has been very happy lately, working lots of good
DX on the bands and teaching it's owner some new tricks :)

Anyhow, when I first finished the KPA100 a month or two ago, I noticed
some high output (like 140W) at times. It happens on 40M (well, that's
the band I'm on usually), and I'll see my wattmeter all of a sudden
start reading up around 140W. Bringing the power level doesn't have an
effect until the rig *thinks* it's down quite a bit lower, like 80W or
70W, then it seems to correct itself and it's fine from there on out,
with max power right around 100W for full-scale power settings.

Originally, we thought it might be due to an oscillation, and I have
replaced C31 (I think thats the one, I forget) with the new value to
stop the oscillations, but I seem to remember Don saying that when
there's an oscillation, the perceived SWR rises, and I don't think
that's happening.

So I'm wondering, perhaps I have a bug in the power sense section?
Maybe a bad solder joint or something?

The problem occurred numerous times the first weekend I had the KPA100
on the air, and hasn't happened since, until today. I was all excited
that the problem had gone away, but I seem to have jinxed myself :)

Any ideas, thoughts, or otherwise?

Thanks,

Jeff N6GQ
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[Don Wilhelm-3]

Jeff,

Yes, look for a solder problem in any of the circuits from the wattmeter
sense (T4) area to the VRFDET output of the KPA100.  Look at the
schematic sheet 1 in the upper right corner (SWR BRIDGE) to identify the
associated components.

73,
Don W3FPR

Jeff Kinzli N6GQ wrote:

> Greetings Elecrafters,
>
> K2 #5945 with KPA100 has been very happy lately, working lots of good
> DX on the bands and teaching it's owner some new tricks :)
>
> Anyhow, when I first finished the KPA100 a month or two ago, I noticed
> some high output (like 140W) at times. It happens on 40M (well, that's
> the band I'm on usually), and I'll see my wattmeter all of a sudden
> start reading up around 140W. Bringing the power level doesn't have an
> effect until the rig *thinks* it's down quite a bit lower, like 80W or
> 70W, then it seems to correct itself and it's fine from there on out,
> with max power right around 100W for full-scale power settings.
>
> Originally, we thought it might be due to an oscillation, and I have
> replaced C31 (I think thats the one, I forget) with the new value to
> stop the oscillations, but I seem to remember Don saying that when
> there's an oscillation, the perceived SWR rises, and I don't think
> that's happening.
>
> So I'm wondering, perhaps I have a bug in the power sense section?
> Maybe a bad solder joint or something?
>
> The problem occurred numerous times the first weekend I had the KPA100
> on the air, and hasn't happened since, until today. I was all excited
> that the problem had gone away, but I seem to have jinxed myself :)
>
> Any ideas, thoughts, or otherwise?
>
> Thanks,
>
> Jeff N6GQ

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