[Elecraft] KPA500 Question

[Thomas Kluge]

Hi Jim,

Sounds like an issue with the T/R circuit, you'll find some reports in
the history of this list. I had a very similar case just one week ago -
in my case it was R7 which was blown. The original type seems to be a
51 Ohm (type 1206 SMD) resistor - I've used now two 100 Ohm 1/4 watt
resistors in parallel... Please check the diodes D8 and D9 if the
resistor is ok - but in my case it was very obvious: At least I've seen
the remainders of the SMD and not just a black spot (as others reported
earlier)...
Taking the PA apart and put everything back together took more time
than the repair ;-)

Best regards
Tom, DL3DTH


Am Sonntag, dem 18.04.2021 um 17:36 -0400 schrieb ws6x.ars at gmail.com:
> I just purchased a used KPA500 (SN 0456) from a close friend. The amp
> was
> just back to the factory for several repairs and was thoroughly
> tested. The
> report reads, "KPA500 #0456 meets or exceeds all factory
> specifications." My
> friend unboxed the amp and made several QSOs to be sure all issues
> were
> fixed. He then personally delivered the amp to my QTH.
> Over the weekend I got the amp added to my operating position and was
> quite
> surprised to find that input signals are attenuated significantly
> when the
> amp is switched from STBY to OPER. No, this is NOT the issue with
> having the
> aux cable and the PA key line connected at the same time. This is
> with NO PA
> key, and NO aux cable connected. The amp has no connection but RF
> input and
> output. It is independent of band. This is with a matched antenna,
> band
> switched manually with the front panel buttons. When I engage OPER
> the input
> signal is attenuated by ~20 dB.
> On the TX side, the amp is fine. On most bands I get full rated
> output into
> a dummy load with approx. 20 Watts of drive from the K3.
> I noticed on the service report, one of the tests was, "Tested
> receive
> attenuation and IMD." I'm curious about "receive attenuation." This
> would
> seem to be related to my problem. Looking at the block diagram, I
> surmise
> something in the TR switch is malfunctioning.
> Before I bug an already-overloaded Elecraft support, I am open to
> suggestions. Am I missing something obvious?
> TIA es 73,
> Jim - WS6X
> P.S. Yes, I have read the manual, and scoured the archives. The only
> thing I
> can find regarding input attenuation in the OPER mode involves
> incorrect
> cabling.      
>
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