[Elecraft] K2 Rev B problems and solutions

[A. Hansen]

This note is primarily directed to K2 builders who bought an early K2, but 
didn't build it, then bought the updates to a Rev B level, and are constructing it 
now or will in the future. 

After almost a year and a half since I ordered it I finally got around to 
building my K2. As John Lennon said, "Life is what happens to you while you're 
making other plans." But now the deed is done and the unit is working well in 
the basic CW configuration. 

I love the radio for all the reasons seen in many postings, so no need to repeat them. 
However, other tardy K2 constructors may find themselves in the same situation I did, 
hence this note. Early this year, having heard about the updated/revised K2, I 
purchased the conversion to the K2, Rev. B, which provides new printed circuit boards, 
revised documentation, and additional parts. Also an updated serial number (#2527 became 
#3302). During construction -- testing actually -- there were three problems, one of 
them self-inflicted. 1) No sidetone, 2) Massive "chirp" on both transmit and receive, 
and 3) PA shutdown due to high current. That last one was due to my installing a couple 
of transistors in the wrong positions and was easily diagnosed and fixed. As for the 
first two problems:

NO SIDETONE. I dutifully checked all parts and connections, resoldered, signal traced, 
and so on. Nothing made any difference. What was I missing? Well, thanks to the list 
archives I found the information about accessing the ST L menu, optionally setting a 
value, and then tapping DISPLAY to force the rig to get it's sidetone from the correct 
source (U8, pin 4 instead of U6, pin 25). 

Recommended acition: This information is currently not in the manual, but it has to be be 
there or in an addendum, not just buried in a list archive.

CHIRP. The receiver is very sensitive and all tuning ranges and other parameters came 
right in spec. But while tuning any signal, there was a chirp or warbling with every 
frequency step as the main tuning dial was turned. Also, the transmitted note was all 
chirp, with only very slow dashes being long enough to allow the note to settle to a 
final pitch on an external receiver. Again, long troubleshooting sessions, resoldering, 
tracing with a scope, and so on. No joy. Any proximity of my hand to the synth circuits 
and other portions of the RF board caused the received signals to vary in pitch. Finally, 
I found that RFC15/C91 "mod" to the RF board (documented in an addendum to the manual) 
was the culprit. I removed the two parts and put in a jumper to bridge the trace that had 
been cut between U4, pin 16 and the nearby circuit trace. Voila! The receiver warble was 
gone and the transmitted CW signal was perfect. 

Recommended action: Revisit the design of this "fix" because it is not universally 
applicable. Maybe a different approach is needed, or at least a better selection of 
component values or better parts placement on the board.

Sorry to dwell on these two problems. I just don't want anyone else to trip over these 
problems as long as I did.

73,
Gus / KB0YH

email: KB0YH@arrl.net