[Elecraft] K2- VCO adjustment problem

[Don Wilhelm]

Laurie,

Your VFO is obviously oscillating, but at the wrong frequency - so look
carefully at the components in the VFO range selection area (see the
schematic RF Board sh 1 of 4).  Be certain the varicap diodes are inserted
the right way 'round, the capacitors are all the correct value and that the
relays are operating properly - the relays are latching type, so you can set
the K2 to the band you want to check, remove power and check which relay
contacts are closed with an ohmmeter.

I believe the other conditions will fall into line when you get the VFO to
tune the proper range (but you may have to add the turn back on T5).  I
would bet that everything else may be working, and what you are really
observing is the efforts of the circuits driving R30 to pull the VFO into
the correct frequency range - giving you the constant high voltage on R30
(and the zero volts on pin 6 of U6 - that voltage will vary with tuning, but
pin 7 that should have a constant 4 volts).

73,
Don W3FPR

"Life is what happens when you are making other plans"
(John Lennon wrote it in a book, Mike Cross used it in a song - I don't know
who was first)

----- Original Message ----- 

> I have a very stubborn problem with the VCO or PLL.
>
> This is in reference to Alignment and Tests, Part II.
>
> 1) The PLL reference oscillator results are very good.
>
> 2) Problems start here: With the 80m band selected and VFO set for 4000.10
> the frequency counter reading is 4248 KHz instead of in the 8 to 10 MHz
> range. (This frequency was verified with a HP frequency counter and it
gave
> the same results as the built in frequency counter.)
>
> 3) The voltage at the left end of R30 remains constant at 7.98 volts. No
> matter what band or setting of L30.  L30 was removed and tested with an
> inductance meter and it works perfectly.
>
> 4) Parts were checked for reverse installation.  All appeared to be ok.
>
> 5) The small PC board with the thermistor was removed, all joints appeared
> ok, then reinstalled.  Same results.
>
> 6) One big question :  The voltage on pin 6 of U6 is 0.000.  The manual
says
> it should be 4 volts.  Does anyone have an explanation for that voltage or
> the other problems.  Also, the board was checked by myself and others with
> no discoveries of bad joints.
>
> 7) One turn was removed from the primary (red winding) of T5.  No change
in
> the results.
>
>     If anyone has any insight into these problems, I thank you in advance
> for any input.
>
> Laurie, VE1AWJ
>
>
>
>
>
>
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