Pat, Thank You for detailing the repair as this seems to be a common problem. So far, I've had KPA3A failures on 2 different K3S radios. That said, the radios gave many years of outstanding service before the KPA3 failed and I'm hoping for many more good years as I love the K3S radios!. 73, Dick- K9OM In a message dated 2/13/2025 12:14:14 PM Eastern Standard Time, elecraft-requ...@mailman.qth.net writes: Send Elecraft mailing list submissions to elecraft@mailman.qth.net To subscribe or unsubscribe via the World Wide Web, visit http://mailman.qth.net/mailman/listinfo/elecraftor, via email, send a message with subject or body 'help' to elecraft-requ...@mailman.qth.net You can reach the person managing the list at elecraft-ow...@mailman.qth.net When replying, please edit your Subject line so it is more specificthan "Re: Contents of Elecraft digest..." Today's Topics: 1. K3S - KPA3A High Power Module Failure - Fixed (Pat Griffin) 2. KX2 I/Q output board (Alan Bloom) 3. Re: K3S - KPA3A High Power Module Failure - Fixed (Michael Carter) ---------------------------------------------------------------------- Message: 1Date: Wed, 12 Feb 2025 14:37:59 -0700From: "Pat Griffin" <wa6...@gmail.com>To: <elecraft@mailman.qth.net>Subject: [Elecraft] K3S - KPA3A High Power Module Failure - FixedMessage-ID: <004901db7d96$6348bf80$29da3e80$@gmail.com>Content-Type: text/plain; charset="us-ascii" My K3S (s/n 10440) developed an intermittent fault a few months ago where itwould unexpectedly drop to "0" watts on transmit, and the receiver woulddrop about 20 dB in sensitivity. The fault initially corrected itself aftera few minutes, and could sometimes be resolved by briefly pressing the"Tune" button on the radio. However, eventually it became continuous. After some experimentation I discovered that turning the power down below 12watts (8 watts on 6 meters) solved the problem. I now had a perfectlyfunctioning 10 watt version K3S with a non-functioning KPA3A internalamplifier. I was able to bypass the faulty module in the Configuration Menu. I then turned my attention to diagnosing and fixing the problem. First, Itested the components and 12v relay on the KPAIO3A interface board whichcontrols the KPA3A. All tested OK. Next, after reading through similar fault discussions on this reflector, Iconcentrated on the PIN diode T/R switching circuit on the KPA3A board.Specifically, I checked the PIN diodes D5 and D8, and the red toroid RFchokes L1, L3, L4 and L5. All checked OK. Stumped, I then went back to this reflector's archives and searched for morerelevant discussions and ideas. Finally, I ran across two discussions from2020 entitled "K3S - No high power output - Low power OK" and "[K3S]intermittent RF path interruption." These both described a known issue withthe solder connection of a critical resistor, R5. This resistor does notmatch the footprint mechanically on the PC board, so a solid connection isnot possible. As the board went through many heating and cooling cycles overtime, this fragile solder connection would eventually break. According to the discussion, Elecraft acknowledged the problem with Rev D ofthe KPA3A PC board, and corrected it beginning with Rev E. My radio is anearly production model and has a Rev A board, and it has the same issue.However, I have never seen a notification or application note from Elecraftconcerning this issue. I then examined R5 on my KPA3A board, and it was partially tucked under RFchoke L1, with a small amount of silicone obscuring the label. Aftercarefully cutting away the silicone, I gently touched the side of theresistor nearest the edge of the board with a thin dental tool. Itimmediately lifted up off the board. I had found the problem! In the schematic I saw that the other side of R5 (away from the edge) iselectrically connected to C17. As it was also physically close to C17 on theboard, I re-soldered that end of the resistor to the same solder pad as C17,which allowed me to re-position the other side of R5 to access the solderpad that was originally underneath the resistor. This fix was successful,and I have now been operating the radio at 100 watts, with no receiverissues, for about 10 hours. I was fortunate enough to have access to the right tools (and eyesight) towork with small surface mounted components like this resistor, but noteveryone can. As earlier production K3S radios get older, it is likely thatthis failure will become much more prevalent. As this was basically theresult of a latent design/assembly flaw, I hope that Elecraft will assistthose who are unable to make the repairs themselves. 73 de Pat / WA6SCW ------------------------------ Message: 2Date: Wed, 12 Feb 2025 21:57:54 -0700From: Alan Bloom <n...@sonic.net>To: Elecraft Discussion List <elecraft@mailman.qth.net>Subject: [Elecraft] KX2 I/Q output boardMessage-ID: <207f02de-b09f-41df-9beb-34c365706...@sonic.net>Content-Type: text/plain; charset=UTF-8; format=flowed Does anyone have excess to their needs one of those little plug-in boards that provide I/Q output from the KX2?? Either the UC6UAA model or the Elekitsorports one designed by BG6JJI.? I'd like to buy one do some experimenting. Please reply off-list. Alan N1AL ------------------------------ Message: 3Date: Thu, 13 Feb 2025 14:09:08 +0000From: Michael Carter <mike.car...@unh.edu>To: Elecraft Reflector Reflector <Elecraft@mailman.qth.net>Subject: Re: [Elecraft] K3S - KPA3A High Power Module Failure - FixedMessage-ID: <bl3p223mb0385c6582331ce74246b3bc5e4...@bl3p223mb0385.namp223.prod.outlook.com> Content-Type: text/plain; charset="iso-8859-1" Hi Pat, Thanks very much for taking the time to carefully document and report your fix of the intermittent RF signal path in your KPA3A. While I have a much newer KPA3A in my old K3 (non-S) radio, it's good to know what you've learned by diagnostic effort and successful repair. 73,Mike, K8CN ------------------------------ _______________________________________________Elecraft mailing listPost to: elecr...@mailman.qth.nethttp://mailman.qth.net/mailman/listinfo/elecraftYou must be a subscriber to post.Elecraft web page: http://www.elecraft.com End of Elecraft Digest, Vol 250, Issue 10***************************************** ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net
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