[Elecraft] K-2 PLL Reference Oscillator woes

[Howard W. Ashcraft]

The PLL is not oscillating--there is no frequency at TP3.  It is not the frequency counter.  The counter accurately reads the BFO and one side of crystal X1.

I have checked all of the components in the oscillator (all correct, proper polarities) and have checked (many, many times) for any evidence of cold joints, bridges, etc.--everything is clean.  The thermistor board looks very good, and to the extent possible (resistance measurements) checks out.  The voltages on Q 19 are correct, and I can read a frequency (slightly fluctuating) on the side of X1 connected to L31. The other side of the crystal is dead.  Everywhere in the circuit shows voltages, but no frequency--all the way to TP3.

One thought I would appreciate comments on:  Both of the diodes, D-16 and D-17, when measured in place, show a resistance of 16.35 k between their pins, regardless of polarity.  Seemed odd, so I checked another ISV149 diode (D-21) and found that it exhibited a resistance of 25.4 M in one direction, and had an infinite resistance in the other direction.  I know that measuring components "in circuit" can lead to erroneous results, and I could be measuring a resistance through RP2, but it seems odd that the resistance would be the same in both directions and is inconsistent with the measurement of D-21.  Does it look like the diodes are bad?

Any other thoughts on why the PLL is dead?

Thanks.

HOWARD W. ASHCRAFT, Jr.
W1WF