K2 alignment issue

[Dan Grizzard]

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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[Don Wilhelm-4]

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.

[hidden email] 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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