Posted by
Don Wilhelm-3 on
Jun 13, 2007; 12:13am
URL: http://elecraft.85.s1.nabble.com/Strange-KPA100-behavior-tp449005p449008.html
Mike,
Fine, and thanks for clarifying that you do have the latest level KPA100.
The fact that you have lower than expected resistances at R26 and R27
suggest that you may have something wrong with U5 (it could be damaged).
Initially, you should make the DC voltage measurements on U5 and U6 and
Q10 and Q11 (see the DC voltage chart at the end of the manual).
The prime suspects for a problem like yours are D16 and D17, T4, U5, U6
Q10 and Q11 - of course the associated resistors can be suspect too, but
are usually not a problem if it worked before. (if it has never worked,
check the resistors associated with the devices listed above (see the
schematic to identify the resistors).
Since your KPA100 is producing maximum power, I suggest that you remove
the power from the KPA100 and feed only the DC coaxial connector on the
base K2 - that will limit the power output to the QRP level (but it will
still produce maximum power from the base K2, so keep the keydown
periods short.
If the DC voltage measurements check out with no problem indication, I
can help you trace the detected voltage from R26 through to the VRFDET
signal.
73,
Don W3FPR
Mike Geddes wrote:
> Don,
>
> This evening I have had a chance to look at my KPA100 again. I verified
> that I am still unable to control output above 11 watts . . . . above
> 11 watss it is putting out 165 watts (connected to Bird 43 meter) and
> showing 7:1 SWR on K2 display. Below 11 watts the output seems correct.
> I was incorrect in an earlier email.
>
> I DO have blue toroids at L16 and RFC1, and L15 is empty. I did verify
> that C31 is .22mF (m22J63).
>
> I checked T4 . . . looks okay and I seem to have proper resistance
> between 1/3 and 2/4. And I do have continuity between 1/4.
>
> One curious observation . . . as I was working through the check and
> alignment process again, I can only get 26.5k and 27.1k out of R26 and
> R27, versus the 43k recommended for C1 adjustment.
>
> Not sure what to look at from this point? Sorry for the prior
> misinformation. Any suggestions?
>
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