k2 test rx v.poor

[Chris-584]

hi im at the stage with k2 sno 6436 where i have done alignment & test part 2
pll,vco,bfo, all tested ok with good ranges. vfo linearization ok, but next
to no audio noise in my headphones on recive (audio side tone good and strong on test)
if i send some v,low rf from my old icom on 40m i can hear it but verry week.rf pre amp
makes it a little better .att kills it. if i have some low  rf at 5.915mhz on a wire and put it neer
u11 or u12 i can hear the signal verry strong. neer to q22 its week agc, fast/slow/off
has no effect, could this be down to u4 on control board its out put is 7.55v i am
waiting for a new one from elecraft my last 3 k2's worked like a dream i would
be happy to recive any help thanks chris g0wfh
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[TF3KX]

Hello, Chris:

I have seen occasional references to low sensitivity of the K2 during construction, and the reasons may vary.  During the ongoing construction of my own K2 (#6425) I had similar symptoms as you have, and finally found out that U12 was bad.  I started a thread on this on 17-March, and you may check out if the symptoms of your unit, and the measurements, are the same as I had.  Incidentally, I received all kinds of suggestions to cure the problem, except the correct one - replacing U12.  So, I wonder how prone these chips are to failing...

If you come to the point of removing U12, it may not be straightforward.  I had  been given the advice of cutting the chip leads, and then solder each "foot" individually out of the board.  In my case this did not work out successfully, so finally I simply desoldered each pin using a vacuum pump as far as I could.  When all of the pins were reasonably solder free I used long nose pliers to loosen each foot in its hole (from the board bottom side) while keeping the remaining solder molten with my soldering iron.  This way I was able to loosen up all eight feet in the mounting holes and then pull the chip out of its place.

73 - Kristinn, TF3KX  http://radio.tf3kx.googlepages.com

Chris-584 wrote

hi im at the stage with k2 sno 6436 where i have done alignment & test part 2
pll,vco,bfo, all tested ok with good ranges. vfo linearization ok, but next
to no audio noise in my headphones on recive (audio side tone good and strong on test)
if i send some v,low rf from my old icom on 40m i can hear it but verry week.rf pre amp
makes it a little better .att kills it. if i have some low  rf at 5.915mhz on a wire and put it neer
u11 or u12 i can hear the signal verry strong. neer to q22 its week agc, fast/slow/off
has no effect, could this be down to u4 on control board its out put is 7.55v i am
waiting for a new one from elecraft my last 3 k2's worked like a dream i would
be happy to recive any help thanks chris g0wfh
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Elecraft web page: http://www.elecraft.com