[Elecraft] K2 VCO Alignment Issue

[Don Wilhelm]

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
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>