http://elecraft.85.s1.nabble.com/Setting-the-AGC-Threshold-on-K2-tp384636p384638.html
Don I worked with him last night, he has it all going it was a cold solder
joint on RP6 so he didn't have the 8 volt line. He's got it working
now....we emailed off the list. (Sometimes I forget to hit the reply all.)
Gregg R. Lengling, W9DHI, Un-Retired
> Jeff,
>
> Try measuring the voltage at U2 pin 5 again making certain your probes
> both
> have good contact.
>
> The voltage at U2 pin 5 is determined only by a resistor network - if it
> is
> still quite low, check the voltage on the 8A line - the output of
> regulator
> U4 (upper leg) - it should be 8 volts.
>
> If you have 8 volts at U4, then check and re-check the soldering of
> Control
> Board RP6, R1 and U2, then remeasure. Remember that the voltage is
> determined only by a resistive network (which includes the RF Gain pot),
> there are no active components involved, so if the voltages to the
> resistors
> and the connections are proper, you should achieve the correct voltage for
> the AGC Threshold.
>
> Be aware that the voltage for the AGC Threshold may not be optimum for
> your
> K2. After your K2 is fully built, aligned, and everything is working
> properly, you can optimize the AGC Threshold so that the AGC does not
> become
> active with no signal into the K2 antenna - so don't be concerned if the
> 3.8 volts is near the upper limit, I find that the optimum setting will
> vary
> from a low of 3.65 volts to a high of 3.78 volts.
>
> 73,
> Don W3FPR
>
>> -----Original Message-----
>>
>> I've just completed the first alignment and test and everything
>> checks out except setting the AGC threshold.
>>
>> When I put the probe of my DMM on pin 5 of U2 (a hellish place to get
>> consistent readings) and adjust R1
>> I get only .002 DC volts.
>>
>> I've resoldered the pins on both U2 and R1. I've looked through
>> Troubleshooting and the Reflector and
>> haven't found anything relevant.
>>
>> By the way I had no trouble with the S-Meter alignment which is
>> dependent on the AGC threshold.
>>
>> Is there any place else I should look on the control board for a
>> possible source of trouble, or could U2 or
>> R1 be defective? (I know components are rarely defective).
>>
>> TIA,
>>
>> Jeff
>>
>> KG6ZVT
>>
>
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