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 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 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?
__
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