[Elecraft] [K2] Odd AGC problem with K60XV installed

[Bill Coleman]

Well, it was on receive that the S-meter would pin, and the audio output would be muted, hence AGC….

> On Dec 16, 2020, at 3:19 PM, Don Wilhelm <donwilh at embarqmail.com> wrote:
> 
> Bill,
> 
> I am glad to hear it has not re-occurred.  I think your analysis is correct, except that it would be ALC and power control that would be affected, not AGC.
> 
> 73,
> Don W3FPR
> 
> On 12/16/2020 3:07 PM, Bill Coleman wrote:
>> Don,
>> 
>> Just a quick follow-up. I’m going to close the book on this problem, as it has not come up again, despite leaving the K2 on a couple of days.
>> 
>> I think your diagnoses was spot on, I think a 15 MHz oscillation of the K60XV VRFDET components was causing the K2 to think the AGC was being activated under certain conditions.
>> 
>> I think the oscillation might have been precipitated due to some waxy flux left between the pins of the LM368.
>> 
>> Thank you for your assistance, as always.
>> 
>>> On Dec 7, 2020, at 8:35 PM, Bill Coleman <aa4lr at arrl.net> wrote:
>>> 
>>> I’m going to set it up in the damp basement at my other QTH. That’s where I saw the problem originally. Will let you know if it comes back.
>>> 
>>>> On Dec 7, 2020, at 11:43 AM, Don Wilhelm <donwilh at embarqmail.com> wrote:
>>>> 
>>>> Bill,
>>>> 
>>>> It does sound like it is fixed.  Just be aware that some intermittents do find their way back, so knowing the symptoms you can recognize it quickly.
>>>> 
>>>> 73,
>>>> Don W3FPR
>>>> 
>>>> On 12/6/2020 6:30 PM, Bill Coleman wrote:
>>>>> Don,
>>>>> 
>>>>> I set the K2 up this weekend to try to reproduce this problem. Once again I opened it up and re-installed the K60XV board. I put a scope probe on P1 pin 6.
>>>>> 
>>>>> I did not see the AGC failure mode right away, but I did find an intermittent oscillation on pin 6 at about 15 MHz. It would come and go, but no AGC activation.
>>>>> 
>>>>> I removed the board and re-soldered all the components around the LM358. Then I inspected the board and scraped away any residual solder flux in that area of the board between any pins.
>>>>> 
>>>>> I also re-soldered the 4.0 MHz resonator, although I did not hear or detect any relay activation when it failed before.
>>>>> 
>>>>> After that, I put the board back in with the scope probe and ran it on the workbench for a day. I saw no AGC failure mode and no more 15 MHz oscillation.
>>>>> 
>>>>> So, maybe it is fixed? Fingers crossed.
>>>>> 
>>>>> 
>>> Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
>>> Web: http://boringhamradiopart.blogspot.com
>>> Quote: "Not within a thousand years will man ever fly!"
>>>            -- Wilbur Wright, 1901
>>> 
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>> Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
>> Web: http://boringhamradiopart.blogspot.com
>> Quote: "Not within a thousand years will man ever fly!"
>>             -- Wilbur Wright, 1901
>> 
> 

Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
Web: http://boringhamradiopart.blogspot.com
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901