K2 VCO Alignment

[David Haas-2]

I'm stuck again fellas.  I'm on the Part II Alignment and Test.  Everything was going so well....
4 MHz Oscillator Calibration......................passed
PLL Reference Oscillator Range Test.......passed
VCO 8-10 MHz  Test.............................  passed
VCO 6 V Alignment.................................passed
VCO Voltage Readings............................failed!!!!!!!!!!!

The voltage readings on 80, 17, 15,12, & 10 meters are fine.

The 40 meter reading is .03V and doesn't change with  frequency change
The 30 meter reading is 8.13V and doesn't change with frequency change
The 20 meter reading is .03V and doesn't change with frequency change.

I've checked the capacitors (C71-C74) and diodes (D21-D26) All are placed correctly with good solder.
L 30 is also correct
I bought my toroids from Mychael so T5 is good.
Any ideas?

Dave N1PT

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[Jim Younce]

David:

In checking the truth table for the VCO I find that there are no capacitors
common to all three bands.  However in checking the relay truth table I find
that K14 is common to all bands that you are having problems with.  You
might want to check the solder connections on all the pins of  K14.  However
I also notice that K14 comes in to play on the 12 meter band.

I think you can assume that all other circuits in the PLL are working
properly since you get a lock on all other bands.. It almost has to be with
C71, C73, or C74 or Relay K14.  I would also check to make sure the correct
type varicap is installed in D21 & D22. They should be the smaller of the
varicap diodes.  You might want to check to make sure the cut off pin on
those two are not shorting out to the board.

I am pretty sure that the 8.13V on 30 meters indicates and unlocked PLL.  I
would double check and make sure that values of C71, C73 & C74 are correct.
Make sure that you dont have a 470PF in place of the 47 at C73 and make sure
that C71 is an 82 and not 820PF.

73 & Good Luck
Jim Younce K4ZM
K2  SN: 18


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