[Elecraft] More data on my K2 problem

[Don Wilhelm]

Woodie,
In addition to your 15 and 17 meter problem (see my prior email), I have 
the following questions.

Is that the maximum or minimum frequency?
A few K2s need additional range for the capacitors around the crystal.
If the frequency is too high, it is easy to lower it with a parallel low 
value capacitor (try 10pF).
If that drives it in the wrong direction, you will need to reduce the 
value of C21 - try 27pF and if that is not enough try 22pF.

Be certain your frequency counter is truly accurate.  I can do that 
measurement with my frequency counter, but it is accurate to 10exp-9.
If you have any doubt about that counter accuracy, use the N6KR method 
when tuned to the highest frequency WWV signal that you can receive. 
Details on this method can be seen on my webpage www.w3fpr.com - article 
on K2 frequency calibration.

73,
Don W3FPR

On 5/18/2017 8:28 PM, woody wrote:
> Took more measurements, Ref the K2 manual (Rev C) Pg 57, 58...
> -----------------------------------------------------------------
> _4 MHz Osc Cal_:
> Setting C22 with well calibrated outboard counter, the counter at TP3
> indicated 12,096.62.  As close as C22 would adjust was a K2 display of
> 12,095.89.
>
> _PLL Ref Osc Range Test_
> Ref High Freq = 12.104.37
> Ref Low Freq = 12.08237
>
> _VCO Test
> Voltage readings_ (left end R30)  Note (*) that in the table below the
> band progression still has  15M and 18M progression *reversed* (see
> earlier, below).  Also note ZERO volts at 18000 !
>
> 3500 - 2.06 volts
> 7000 - 2.98
> 10000 - 5.13
> 14000 - 4.27
> * 21000 - 8.22
> * 18000 - ZERO (0.02v)
> 24.800 - 6.82
> 28000 - 4.74
>
> Hope this is some help.   Thanks again,  Woody
> ------------Earlier email is below----------------
>
> On 5/18/2017 20:18, woody wrote:
> Hello,
>
> I have an elderly K2 (S/N 02600)  that had been working well. After all
> these years, it was about 200 Hz off frequency so I proceeded to do an
> alignment.  Got it pretty close, but the trim cap (C22) would not pull
> quite on freq.  Close enough maybe...
>
> Proceeded with band by band alignment / peaking.  All bands peaked as
> expected except 17M, (maybe 15M too)....   No change when adjusting C32
> & C34  for 17M.
>
> More symptoms:
> * Stepping up the bands is normal until going from 20M to 17M. Then:
> 17M and 15M are reversed from normal progression.
> e.g:  160, 80, 40, 30, 20, _*15, 17*_, 12, 10
> * System Rx noise is significantly reduced on 17 & 15.
> * In CW mode, the Tx freq is OK on all but 15 & 17.
>
> The display reads as expected on 15 & 17 - as VFO is adjusted. But, my
> freq counter indicates the actual Tx output freq is different and does
> not change when the display freq is changed:
> Example...  For 17, the Display indicates 18.120, the output is on
> 18.766+-.  For 15, the display indicates 21.265, the output is
> 21.434+-.  It is also receiving on the (actual but wrong) Tx freqs.
> Changing the VFO changes the display but does not change the actual TX
> or Rx frequency which seems to always be the same.
>
> I am stumped!!!   Can you offer any suggestions as to what might be
> happening???
>
> Thanks,
> Woody, KZ4AK   (Formerly WB4QXE)
>