Posted by
John Wingard on
Apr 27, 2019; 9:37pm
URL: http://elecraft.85.s1.nabble.com/K2-VCO-Alignment-Issue-tp7651214p7651220.html
Hi Don,
Thanks for the quick response. I did check C72 again. It is a 271 value. I
then spread the red turns on T5 as far as I could. I'd say they cover about
90+% of the toroid. I put the L30 slug at mid-point of travel and measured
voltage at R30 and it is still right at 8.37 V. While there I checked the
frequency at TP1 and it was 8247.90, which is considerably lower than the
8913 that you expected.
Next I went up to 7100 and measured the voltage at R30. Still right at 8.37
V, no change. Frequency at TP1 @ 7100 was 11558.11.
So, it appears that the frequency at 4000 is not within the expected range,
and likely not at 7100 as well. Hope this tells you something because I'm
stumped.
I've got some plans for this evening so I may not get back on it until
tomorrow afternoon, but if you've got any more things for me to try I will
do them then.
John, WB4GLJ
On Sat, Apr 27, 2019 at 1:57 PM Don Wilhelm <
[hidden email]> wrote:
> John,
>
> That high voltage is trying to reduce the capacity of the varactors.
> Which means there is either too much capacity or too much inductance in
> the circuit.
>
> Check the value of C72 first - it should be marked "271". Then set the
> L30 slug to about mid-position and spread the red turns of T5 enough so
> the starting and ending turns are adjacent. What is the voltage when
> tuned to 4000 kHz? Measure the frequency at TP1 - it should be near
> 8913 kHz.
>
> Then change to 40 meters - 7100 kHz - What is the R30 voltage and what
> is the VFO frequency measured at TP1.
>
> The answer to those questions will help in determining what to do next.
>
> 73,
> Don W3FPR
>
> On 4/27/2019 1:32 PM, John Wingard wrote:
> > Working on my 2nd K2 (S/N 7869) and have run into a problem with the VCO
> > alignment. I'm getting a constant 8.37 V at R30 at 4.000 MHz.. I cannot
> > change it with the full range of L30. Correct type inductor is installed
> at
> > L30. Dropping the VFO down to 3.500 doesn't change it either. I have
> gone
> > back through the archives and read just about every post concerning this
> > problem but nothing I have tried has made any difference. I have double
> > checked all correct parts placements and orientations, re-flowed all
> > connections in the quadrant of the board around the VCO section. T5 is
> > wound as per the manual (from the Toroid Guy) and installed correctly. I
> > have tried both spreading and compressing the turns on T5 with no change
> > either way.
> >
> > Regarding the thermistor board, I have 4.18 V on pin 5 of U6.
> >
> > Test in the previous section were within specs:
> >
> > 4 MHz Oscillator Cal using CAL FCTR was 12099.61 and confirmed with an
> > external counter.
> > Range of the PLL reference oscillator: 12099.61 - 12086.01 = 13.59 kHz
> > VCO oscillator test: 8162.60 MHz
> >
> > I'm about out of ideas at this point. What should I start checking next?
> >
> > Thanks for any help!
> >
> > 73 de John, WB4GLJ
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