As Don indicated, U7 was the problem. After I replaced U7 my KX1 is able to hear again. And after I replaced Q6 I am able to transmit. I’m happy I can use my KX1 again!
Thanks and 73! Matt KS6PKY > On Dec 28, 2021, at 10:19, Matt Stumbo <[email protected]> wrote: > > Thank you Don, > > I ordered a TPS76427 and a couple spares from Digi-Key and will replace U7. > > Any thoughts on what may have caused U7 to fail? ESD comes to mind, though I > used an ESD mat and wrist strap anytime I worked on the KX1. Part infant > mortality also comes to mind. My primary concern is the U7 failure is a > symptom of some other failure I have yet to discover. My worst fear is I put > a new U7 in and it fails the same way. Have you seen U7 fail in other KX1s? > > I ordered a replacement 2SC2166 MOSFET for Q6 from RFParts. I’ll replace it > once I repair the U7 issue. > > 73! > Matt KS6PKY > >> On Dec 27, 2021, at 11:20, Don Wilhelm <[email protected]> wrote: >> Matt, >> >> You likely have a problem with U7. At least, that is the thing that you >> need to resolve first. >> >> Sorry about U6, it usually makes a loud pop when the base and collector are >> shorted. You will have to replace it before you get any power out. >> >> 73, >> Don W3FPR >> >> >>> On 12/25/2021 2:51 AM, Matt Stumbo via Elecraft wrote: >>> I had the pleasure of recently assembling a KX1 and KXAT1 kit. I had the >>> KX1 working on both 20m and 40m, which last worked on Sunday. Unfortunately >>> I now have the misfortune of debugging an issue with it. >>> >>> Today I found the RX and TX no longer work. The KX1 powers on, the menus >>> behave as I expect, the AF gain changes the audio and Filter knob changes >>> the audio, tuning results in the ATU relays clicking but without any power >>> out the tuner doesn’t find a solution and displays 0 W and 9.9 SWR. The RF >>> Gain knob doesn’t have any noticeable affect. >>> >>> I’ve done the following: >>> * Inspected the KX1 for poor solder joints and shorts, found none >>> * Verified R4 is fully clockwise >>> * Verified Q6 collector is isolated from ground >>> * Removed the KXAT1 and jumped J7 pin 1 to pin 3 >>> * Verified TX is 0 W with an external wattmeter >>> * Completed the voltage tables >>> >>> The voltage tables indicated the following issues: >>> * U1 pin 14, expected 0V measured 5V >>> * Most U2 pins do not measure expected. I attribute this to U7 2.7V power >>> output measuring 1V. >>> * U7 pin 4, expected 1.17V measured 0V >>> * U7 pin 5, expected 2.69V measured 1.0V >>> * Q5 Emitter on Tune expected 2.24V measured 1.48V >>> * All other measurements were in family with the expected values >>> >>> The issue that sticks out to me the most is the U7 pin 5 output is too low. >>> This results in the DDS U2 not receiving the power it needs to operate, >>> hence most of the U2 voltage measurements do not match predicts. Is there >>> any reason this 2.7V output could be low besides U7 failure? Are there >>> other areas I should probe not included in the voltage table? The U7 input >>> voltage is good, 5V. Do I need to replace U7? >>> >>> To make matters worse, while I was measuring the Q6 collector voltage, I >>> briefly shorted the base to the collector with the DMM probe. I have not >>> noticed any new issues with the KX1. The KX1 still turns on, the buttons >>> work, etc. Are there parts I should check to make sure I didn’t break or >>> stress anything? ______________________________________________________________ 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]
