[Elecraft] Seeking Help Solving KAF2 Problem

[Dennis Payton]

A couple weeks ago, I got out my K2 and operated the ARRL International DX 
Contest. During the contest, my audio output was so low I had to constantly 
use the preamp just to hear on my headphones, so afterwards I opened the rig 
up and tracked the problem down to the audio filter. Shorting pins 1 & 2 of 
J1 & J2 gave me full audio with the board removed, and flipping the 
board-mounted switch to "out" gave me full audio with the board installed.



That told me the problem 'had' to be in the filter board, but after checking 
the DC voltages from the chart and thoroughly examining each component's 
location and solder joints, I found nothing. I decided to use a RS 
speaker-amp to follow the audio signal through the filter to see where it 
was getting attenuated, but was very surprised to not see it getting 
attenuated anywhere. The filter appears to work properly from beginning to 
end. The audio at pins 1 & 2 of J1 & J2 all sound fine to me, whether the 
filter is switched in or out, but the K2's audio is 'greatly' attenuated 
when the filter is switched in. Although I'd made sure the filters were 
aligned with each other when I first started troubleshooting, I thought that 
was all that was left, so I started checking them again. Then, at one point, 
I hit the "spot" button and discovered I suddenly had no sidetone. I spent 
quite a bit of time trying to figure out what happened, but couldn't get any 
power from pin 25 of the MCU whether I keyed the rig, hit "spot", or turned 
the rig off & on. Then as a curiosity after giving up, I removed the audio 
filter board. That gave me sidetone again! Next, I reinstalled the board and 
I still had sidetone, so something must have "locked up"? Now, I've got the 
filter removed again though, and have decided that I'm at the end of my 
ability.



Something else I think I should mention is that I measure 5.15 volts on pins 
1 & 2 of  J1 on the control board. I hope that's expected. Also, I don't 
know if I've had this problem since the beginning or if it just popped up. I 
haven't operated the K2 since installing the KAF2 quite some time ago, and I 
just don't remember how I left it.



Any advice would sure be appreciated.



Thanks!



Denny Payton    N9JXY



(By the way, I worked Auckland, New Zealand on 40-meters during the contest 
operating one watt. That calculated to be 8312 miles-per-watt, which is by 
far a new record for me. My antenna is just an R7 vertical mounted on a shed 
in my back yard.)