[Elecraft] K2 dial alignment SOLVED!!

[paul]

Last year, I upgraded my K2 from rev A to Rev B.  Afterwards the dial was 
off by 12 KHz at 10MHz, even after setting the 4Mhz crystal, doing CAL 
PLL, CAL FIL more than 30 times.  Yes, I followed every procedure posted 
and verified the 4 MHz clock accurately.  Prior to the upgrade, the dial 
was right on.

It turns out that the VCO max frequency must be at least 12096 khz or the 
dial calibration will be off.  This should be in the FAQ, along with how 
to fix it in the upgrade instructions.

After making the rev A to B mod, the VCO range was 12084.87 to 19094.44 
creating the 12Khz dial error - no matter how many alignments attempted.  

Finally I just tried experimenting with the VCO.  I put in another 
crystal in parallel with X1 (that came with the BFO upgrade) in X2.  
The VCO range was 12081.52 to 12098.17 which fixed the dial error, but 
the VCO was too wide at 17.19 Khz.

I swapped out the 12uH inductor (L31) with the old 10uH inductor and got a 
VCO range of 12084.87 to 12094.44 - dial calibration was way off (Yes, CAL 
PLL and CAL FIL were run after each of these changes).

Then I removed the second crystal at X2 that I had temporarly installed 
two steps above.  VCO range now 12090.70 to 12097.63 - BINGO - the 
dial is dead on!!!  The VCO is a little narrow at 6.93 Khz, but I have no 
plans to use 160 meters - so this should be ok.

So the solution was to go back to the 10uH inductor.

I have spent several weekends and nights trying to figure out this 
problem.  While I have learned a lot doing this, please put this in a FAQ 
somewhere and save someone else the trouble.

Paul
AD5IW

On Sun, 2 Dec 2007, paul wrote:

> Hi,
> 
> Recently I started to upgrade my K2 (sn 2592) with the KPA100 kit.  Before 
> I could complete the KPA100 though, I had to upgrade the K2 from rev A to 
> rev B.  I have completed all the revs except for the firmware upgrade - 
> Elecraft sent only the MCU but not the IOC.  It is now being mailed.
> 
> Before the rev, the frequency on the dial matched the received frequency.  
> Now WWV is received on 10.012 MHz.  I have done the calibration of the 4MHz 
> several times - checking with a known good receiver (AOR AR7030+).  I can 
> vary the c22 and zero beat exactly on frequency (USB and LSB) - also at 
> higher harmonics (16Mhz).  I ran an antenna wire next to the 4MHz xtal and 
> listen on the SW receiver.
> 
> After the 4MHz calibration, I have run the CAL PLL and then modified every 
> CAL FIL entry afterwards.   Still no change.  The dial reads 7.010Mhz when 
> hearing 7MHZ and 14.020Mhz when hearing 14Mhz.
> 
> Otherwise, the receiver is excellent - much better than before.  Had a low 
> volume problem before, now it is really loud.  Did all the RF and contol 
> board changes, BFO temp stability mod, PLL upgrade, AF gain smoothness, 
> VFO ALC 10/12 meter band pass filter, AGC threshold (R1 from 51k to 
> 22.5k).  I have checked for bad solder joints or bridges - nothing wrong 
> that I can see.
> 
> I did not do the second crystal filer flatness mod or the sidetone mod 
> yet.  Also no firmware had been changed yet.  Any ideas what to check?
> 
> Thanks,
> 
> Paul
> AD5IW
> 
> Here are some measurements when receiving 10MHz WWV: 
> 
> TP1  14913.05
> TP2   4913.19
> TP3  12089.38
> 
> Dial: 10011.99
> 
> -------------------Range measurements
> PLL
> min: 12083.69
> max: 12094.29
> range:  10.60
> 
> TP1
> min: 14906.04
> max: 14919.09
> range:  13.05
> 
> BFO 
> min:  4916.99
> max:  4912.59
> range:   4.40
> 
> R30:  4.34V 10MHz
>       5.70V @ 4MHZ
>       2.02V @ 3.5Mhz
>