[Elecraft] K-1 TR Abnormality

[Brian Kassel]

Gang:

   A while back my K-1 took a high voltage hit  through the antenna 
connector, forgot to disconnect from an ungrounded antenna.  The 5V RX 
TR signal was being pulled low, so I replaced Q-4, the ZVN4424A, and 
everything seemed to work just fine on a dipole antenna. Then I noticed 
a strange thing: whenever I connected an antenna that had a DC sort at 
the feed point of the antenna, like in a BETA match, the RX goes dead! 
The transmitter works fine. I have the antenna tuner option, and I was 
able to eliminate that board as the problem by simply bypassing it via 
J-2 on the filter board.  Obviously something is shunting the RX signal 
to ground.  I took my ohmmeter and found no place in the RX path  that 
shows a low resistance to ground. I am guessing that the problem is in 
one of the 1N4007 diodes in the TR circuit that is biased on when in RX, 
but shunts the signal to ground only when the receiver is on.  Now I 
have a drawer full of  1N4007's, but I would like to be able to nail 
down the problem a little closer that that if possible.

  Interestingly, I had the same set of circumstances nail my K-2, but a 
previous post found in the archives gave me exactly what I need to 
repair the radio back to 100%, only $6.50 worth of parts, including 
shipping from Elecraft. I am betting that someone on the list has 
suffered the same type of failure, and has gone through the exercise.  I 
did check the archives, but I didn't find any post that seemed to apply. 
If not, I'll just begin replacing the diodes one by one. Please reply to 
me directly, AND to the list, as I get this list in digest form and I 
would like to get this puppy perking again for an upcoming trip. Yes, 
and I will repeat to myself over and over to disconnect the antenna when 
not in use. I promise. ;)

Brian K7RE