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 [email protected]: > 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. > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [email protected] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
