Dick & Don, Thanks for confirming. Although unlikely to be the source of trouble, It also appears U6 and U8 are in the VFWD and VREF circuit paths. I'll order up everything and have it on hand when I replace this week. It could also be a passive problem like a marginally-corroded connector, or failed resistor.
By the way, the problem manifests with high SWR and power set readings that no longer match anything close to actual output power into known good loads. The SWR reading fluctuates excessively with change in the PWR control and slight changes in the control quickly lead to 120W power spikes when the K3 display indicates 15-20W. This tells me the ALC circuit is not getting a good forward power sample. So, it appears the SWR bridge or surrounding circuitry has partially failed. Paul -----Original Message----- From: [email protected] [mailto:[email protected]] Sent: Sunday, January 21, 2018 1:18 PM To: 'Paul Christensen' <[email protected]> Subject: RE: [Elecraft] K3 Power Reading/SWR/ALC Problem I don't know where purchasing actually buys the parts, but... D36 and D37 are BAS70INCT Diode, 70V, SOT23, like Digi-Key BAS70INTR-ND U16 is LM358, DUAL OP AMP, SOIC8, SMD, like Digi-Key LM358DR2GOSTR-ND 73 de Dick, K6KR -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Paul Christensen Sent: Sunday, January 21, 2018 08:02 To: [email protected] Subject: [Elecraft] K3 Power Reading/SWR/ALC Problem I have a K3 at a remote site about an hour north of my home so unfortunately, I cannot quickly investigate an issue that's recently developed. After reviewing the K3 schematics, the root cause is likely isolated to the following parts on the PA board: D36, D37 (BAS70 - Schottky directional coupler sampling diodes), and/or U16 (LM358 dual op-amp used as a voltage-follower). My question: are these three parts leaded or SMT/SMD? Perhaps I'm not looking hard enough on the Elecraft website but I don't see a detailed B.O.M. for the K3/K3s. I want to be ready for replacement without wasting a two-hour trip to/from the site. Thanks. Paul, W9AC ______________________________________________________________ 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 mailto:[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]
