[Elecraft] K2 AGC

[Ed Lambert]

My K2 s/n 1999 was completed in February 2002.

 

Last Sunday, during the EC Nets, I noticed that some strong stations were
actually getting audio signals into my ears that were close to the threshold
of pain. I also noticed they were not "deflecting" the "S" meter one bar.
After some experimenting, I discovered that my agc was intermittent.
Recalibrating it sometimes brings it back to life. Touching pin 7 of U1 on
the control board seems inconclusive for me. I cannot hear the signal on or
about 10.136 MHz, but I have been doing this in the operating position while
standing on my head on a banana peel with three tools in each hand. Maybe
when I get it on the bench I'll be able to hear the signal.

 

At this time I suspect a marginal solder joint somewhere in the signal path
from pin 8 of U12 on the RF board to pin 1 of 1 on the control board, or one
of the pins on U1 or U12, or a bad crystal X1 on the control board. I intend
to do some signal tracing in these areas to see if I can induce the problem
one way or the other. (Simply resoldering all of the joints is a last
resort; I'd prefer to learn something and identify the exact problem.)

 

I am curious about the S meter calibration process since it sometimes seems
to "shock" the system into operation. Can anyone tell me how that process
interacts with U1?

 

I am also curious if the collected wisdom of the reflector has seen a
similar problem and might be able to shorten my search before I start
digging into this.

 

Ed Lambert KD3Y