[Elecraft] Setting the AGC Threshold on K2

[Geoffrey Mackenzie-Kennedy]

Hello Jeff,
Have you tried measuring the voltage at the wiper terminal of R1 (Control 
Board) or RP6 pins 4/5? These points are all connected together along with 
U2 pin 5, so you should get the same voltage +- a couple of millivolts at 
each of these points. The voltage at all these points should vary but remain 
equal as you tweak R1 and be >>.002V, approx 3.8V downwards.
However your .002 volt reading makes me wonder whether or not the probe is 
actually making contact with U2 pin 5 or is sitting on top of a layer of 
gunge that has formed on the IC's pin e.g. corrosion.

73,
Geoff
GM4ESD

 "jrb" <jrbee at best.com> wrote on December 18, 2005 at 1128 PM

> 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).