I'd say the switching FETs have failed. Correctly operating, there is no measurable attenuation in the receive line when in OPER or STBY modes.
As to T/R switching, make sure the amp is in receive and not in transmit when your radio is in receive. Any of the items in the amp display preceded with a * indicates the amp is in transmit mode. If so, something is pulling the KEY line to ground.
73 Bob, K4TAX Message: 1 Date: Sun, 18 Apr 2021 17:36:48 -0400 From:<ws6x....@gmail.com> To:<elecraft@mailman.qth.net> Subject: [Elecraft] KPA500 Question Message-ID:<001001d7349a$f0a01570$d1e04050$@gmail.com> Content-Type: text/plain; charset="us-ascii" 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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
