[Elecraft] K2 VCO Alignment only 0.02V @ R30

[Don Wilhelm]

Jeremy,

I have read your exchanges with Gary,

First, don't bother with the C22 setting - just set it to the midpoint 
(slot parallel with the long edge of the board) and leave it there until 
you have the rest of the K2 receiver working on all bands, and then go 
to my website www.w3fpr.com and do the procedures stated in the K2 Dial 
Calibration article there.

Taking things one step at a time - is the PLL Range correct at TP3? Tap 
BAND+ to bring it to the highest frequency (about 12100 kHz) then tap 
BAND- to get to the lower limit (about 12087 kHz)  Those frequencies can 
vary by 2 to 3 kHz from the target values and still be OK.

Once assured that the PLL Range is correct, then tackle the VFO frequencies.
You do have something wrong there because your frequencies are too low 
on all bands.  That indicates either too much capacity or too much 
inductance is present in the VFO circuit.  Look at the schematic for RF 
Board sheet 1.  The area in question is in the upper right corner - the 
input side of Q18 - as well as the VFO range Select components.

Is T5 wound on a yellow core?  If wound on a red core, it will have too 
much inductance.  Does L30 have a slot across the entire diameter of the 
tuning slug?  It should.
Look at the tops of D23, D24, D25 and D26.  They should have a top shape 
like Q18 and about the same size.  D21 and D22 should have a smaller 
body profile when viewed from the top.  The wider flat side of all those 
varactors should be facing toward the rear of the RF Board.

Your next step is to check the relays K13, 14 and 15.  The white stripe 
should be on the end toward the rear of the RF board.

Examine the bottom of the board for the soldering of those components in 
the VFO and VFO Range Select areas to be certain there are no tiny 
solder bridges.

If everything is correct, it *should* have close the frequencies listed 
in VCO Table on the Schematic Key page - within 3 to 5 kHz when 
everything is correct.

73,
Don W3FPR



On 2/2/2013 9:43 AM, JeremyJones wrote:
> I'm in the process of building a K2 and am having trouble at the Alignment
> and Test part 2.  I've gone through at ton of previous posts here an have
> been talking with Gary at Elecraft but no luck so far.  The main issues are
> C22 only has adjustment less than 1khz (12085-12086) @ TP3, and R30 which
> should have 6V only has 0.02V.
>
> Below is the email chain (bottom to top) with the trouble shooting Gary and
> I went through.  Wonder if anyone has any ideas of what the issue might be,
> or further trouble shooting steps to isolate the problem.
>
> Thanks,
> Jeremy
>
>