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?
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