[Elecraft] KX1 RX and TX Problem

[Matt Stumbo]

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? 

Thanks and Happy Holidays everyone!
Matt KS6PKY