[Elecraft] Re: section II alignment pll problems

[Don Wilhelm]

Dan,

The varactors are changed simultaneously, so the voltage on one should 
be the same as the voltage on the other.  A low voltage should be 
applied when BAND- is tapped and the capacitance will be at a maximum, 
then when BAND+ is tapped, the voltage is made high and the varactor 
capacitance is at a minimum.  In normal operation, the voltage will be 
somewhere between those extremes and will change as the K2 is tuned- 
that is how the K2 tuning is accomplished - it is a phase locked loop 
synthesizer where the PLL reference frequency is varied between each of 
the major tuning increments.  That feat is accomplished by 'pulling' the 
crystal frequency - it is a type of VXO circuit.

Since your frequency of oscillation is considerably higher than what the 
crystal frequency should be, I am suspicious about the crystal itself.  
It is possible that the crystal manufacturer mis-marked it, so I would 
try another one - but still, the frequency should change even though the 
entire range would be higher than normal.  If the crystal were 
completely dead, I guess it is possible for the circuit to oscillate at 
some strange frequency, but that is not likely either since you seem to 
have a stable frequency.  Have you checked the orientation of diode 
D18?  Although if it were reversed, it might kill all oscillation.

OK, enough rambling and speculation on my part - I suggest that you get 
a new PLL crystal from parts at elecraft and install it, then see what 
happens. Check the resistance across L31 before ordering the crystal, if 
the resistance is quite high, L31 could be open and should be replaced 
as well.

73,
Don W3FPR

kf4pob at aol.com wrote:
> I have tried all tests and checks offered up by you good folks but 
> none of them have cured my problem. I have even gone to a local ham 
> buddy that has built one and we both could not find the cure. I have 
> verified that all the parts are correct and in the right place. I have 
> re-soldered all joints, those looking questionable or not. I also 
> verified that the 12597.91 frequency displayed is in fact accurate.all 
> voltages are correct, L31 is correct and capacitors c84 & c85 are 
> correct. When checking the cathode voltages on d16 & d17 the voltage 
> did come and go when hitting the band- and band + buttons. I noticed 
> the voltage came and went on BOTH of the diodes simultaneously. 
> Male logic kicked in and said is that right? If the two diodes are 
> used to vary the frequencies to the display shouldn't they be 
> activated one at a time, one with band+ and one with band-?"
> Thanks in advance for your input.
>