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 <d...@w3fpr.com> 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: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
