[Elecraft] K2– loss of sensitivity

[Don Wilhelm]

Hans,

That is definitely not normal.  The K2 should operate with 11 volts or 
less with no reduction in sensitivity.
Much of the K2 receiver operates from the 8 volt regulator output. 
Exceptions are the preamplifier, post-mixer amp and the audio amp.
Since you say the S-meter reading is low, that should rule out the audio 
amplifier.

I would first check the output of the 8 volt regulator (Control Board 
U4) then check the 8R voltage rail both at the collector of Control 
Board Q2 and on the RF board.  You can easily check the RF Board 8R 
voltage at the anode of D6.  Voltages below 7.6 would indicate a problem.

If the 8R voltages are OK, then focus your attention next on the post 
mixer amplifier stage - RF board Q22.  The DC voltages are listed in the 
DC Voltage chart in the back of the manual.  That chart is for full 14 
volts supplied to the K2, but at lower voltages, the DC voltages should 
be proportional.

Since this is a recently assembled K2, look carefully for connections 
that are not soldered or poorly soldered.

You may have to do Receive Signal Tracing following the procedure in 
Appendix A to determine just which stage is giving the failure.

Good luck with it and 73,
Don W3FPR

On 4/7/2013 8:56 AM, Hans Elfelt Bonnesen wrote:
> K2 # 7359 w/ built-in battery.
> If I turn on my K2 in the battery state the sensitivity is unexpectedly low. ( with 12.1 volts ). One S-unit local noise.
> As soon as I apply the normal charging voltage from the supply (with 13,7volts ) it
> suddenly jumps to normal sensitivity. Four S-units local noise.
> Is this normal, or could something be done ?
>
>