[Elecraft] K2 alignment issue

[Don Wilhelm]

Dan,

The 8.3 volts says that the VCO capacity is too great and the higher 
voltage is trying to reduce the capacity of the varactors.  
Unfortunately, the maximum the circuit can develop is 8.3 volts, so your 
voltage is stuck at maximum for all bands except 80 meters.

I am not certain which "voltage pot" you are trying to adjust - the 
adjustment is the inductor slug in L30 or the spacing of the turns on T5 
(or both).

I suspect you may have an extra capacitor in the VFO Range Select area - 
or that relays K13, K14 and K15 are not being operated properly (those 
are the relays that switch the VFO range capacitors) or that one of the 
varactors is oriented improperly..

Since you can obtain 6 volts on 80 meters, I must ask where the slug in 
L30 is located.  If it is just a few turns down from the top, that is 
OK, but if it is in an extreme position, check the turns on T5 for the 
proper number (count the times the red wire passes through the center of 
the core).  Then set L30 about 3 turns down from the top and adjust the 
spacing on T5 to get the 6 volts at 4000 kHz - once that condition is 
satisfied, check the other bands.

This may be a tough one to troubleshoot, but I would start by making 
continuity checks across the relay contact for K13, K14 and K15.  Refer 
to the relay table on the Schematic Key page to see which of these 
relays are set for any particular band, then refer to the schematic for 
RF Board sheet 1 to see the position of the relays in the reset position.
These are latching relays, so you can turn power on, set the band to be 
tested and turn power off - then use the ohmmeter to determine the relay 
actual position.

Check the varactors D19-D20 (if installed), D21 - D22, and D23 - D26.  
Check for the proper varactor (the 1SV149 has a smaller body than the 
MV209 when viewed from the top). and be certain the varactors are 
oriented properly - if you cannot see the board silkscreen, compare with 
the parts placement diagram at the back of the manual.

Good luck, as I indicated, if you soldered an extra capacitor in that 
circuit somewhere, it may be hard to find.

73,
Don W3FPR

Once you confirm that the relays are in the proper positions for each 
band, then you my conclude that it is not a relay problem.  Next look 
for the extra capacitor in that area.  The VCO table on the Schematic 
Key page tells you which capacitors are to be in the circuit for any one 
band.

af4lb at verizon.net wrote:
> I have recently completed phase III build of my K2 and started the alignment process.
> A couple of problems developed during the alignment so I went back
> and started re-checking phases I and II resistance and voltage checks.
> During the initial construction of these two phases all of the resistance
> and voltage checks were within tolerance ranges. This time the VCO
> voltages were off. I am able to get the 6vdc at r30 with no problem. It
> was fully adjustable to that value. The voltages on 80 meters did drop from
> 6 vdc at 4ooo hz to 1.7 vdc at 3500 hz. When checking the voltages on
> the other bands the voltage was a solid 8.3 vdc and would not vary when moving
> the vfo. The display on the dmm did momentarily fluctuate while moving the vfo
> but then went back to 8.3 vdc. Adjusting the voltage pot  on these bands did not change the 
> voltage either. When I switched back to 80 meters I was able to adjust back to 6vdc 
> as before. Anybody have any suggestions? I have searched the archives and found
> nothing on this subject.
> 73
> Dan
> af4lb
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