[Elecraft] K2 VCO frequency out of range and not changing

[Don Wilhelm]

Gareth,

You did not supply much information with frequencies and voltage 
measurements, so I have to guess a bit about what your problem may be.

Usually when the VCO frequency at TP1 does not change, you will also 
find that the VCO voltage measured at the left end of R30 is at one of 
its extreme voltages - either about 8 volts or about zero volts.

The solution is to either adjust L30 or adjust the turns on T5 (or both) 
to get the frequency of the VCO into a range where the PLL can adjust it.

The easiest way I can tell you which way to move the frequency at TP1 is 
to tell you to look at the VCO table on the Schematic Key page (the 
first page of the schematics near the back of the manual.
Set the frequency on the VFO dial to the low end of a band (80 meters - 
3500 kHz is good).
Then measure the frequency at TP1 and compare it with the VFO frequency 
shown in the chart (for 80 meters it is 8415 kHz.
If the frequency at TP1 is too high or too low, adjust the turns of T5 
or adjust L30 to bring it onto frequency.  For gross adjustment, adjust 
the T5 turns spacing, and for fine adjustment use L30.
Note - if the frequency at TP1 is WAAAAY off, you may have a problem 
with the capacitors or relays in the VFO Range Select area.  See the RF 
Board schematic sheet 1.  The Schematic Key VFO chart tells you the 
capacitors used for each band - check the value and soldering and check 
the soldering of relays K13, K14, and K15.

Once you have the right frequency when tuned to 3500 kHz, tune to 4000 
kHz and measure the voltage at the left end of R30.  It should be able 
to be adjusted to something near 6 volts, and can then proceed to check 
the other bands as normal in the manual instructions.

73,
Don W3FPR

On 7/2/2014 9:35 AM, Gareth - M5KVK wrote:
> Hi
> I bought a K2 kit way way back; started to build it but then got distracted: divorce, moving, re-marrying - you get the picture:-) I’ve finally got back to it and have just started on Alignment 2.
>
> All is well until I check the VCO frequency at P1. It is out of spec and doesn’t change when I spin the dial. The display does, but not the VCO frequency.
>
> The VCO does change when I change band.
>
> I’ve checked through and the PLL is working, there is data in to the PLL and the VCXO works OK.
>
> It all looks OK, so I’m not sure where to look next. The varactor diodes maybe?
>