[Elecraft] K2 VCO alignment problem

[Charles Vollum]

K2 #3632 is now in the part 2 alignment and test phase.  All RF board 
resistance checks on page 56 are OK.

On page 57, all goes well.  The 4 MHz oscillator is left uncalibrated 
for the moment.   PLL reference oscillator at TP3 shows a high 
frequency of 12099 and a low freq of 12086, for 13 kHz range -- well 
within spec.  VCO at TP1 showed stable 8906 on the FCTR, looked good.

Page 58 starts well; no problem getting 6.0 V at R30 by adjusting L30.  
After this, things go haywire.  Setting the VFO to 3500 gives 0.01 V at 
R30.  More precisely, if 4000 kHz gives 6.0V, then 3800 kHz gives 1.5V, 
and 3755 or lower gives 0.01V.  If I set L30 so that 4000 kHz gives 
7.5V, then 3760 gives 1.5V, and 3715 or lower gives 0.01V.  Similar 
behavior occurs on the other bands, with much too narrow a voltage 
adjustment range.

I assembled the RF probe and checked signal levels per appendix E page 
10 and 11.  Reference oscillator output, VCO output, VCO Buffer output, 
BFO output and BFO buffer output are all nominal.   I also did the BFO 
range tests on page 59, and everything is fine there.

I have double checked the winding and installation of T5, that L30 is 
the right inductor, that the varactors D21-26 are the right ones, and 
that C71-C74 are all the right values.

Any suggestions on how to proceed?

Thanks,

Charles N7BPT

ps -- I'm having troubles with my normal email address, moana@xsw.com.  
Please cc replies to vollumc@mac.com.  Thanks!
----
Charles Vollum
http://xsw.com/boojum -- Boojum, a trailerable offshore tug yacht