[Elecraft] K2 PLL Reference Oscillator failure

[Don Wilhelm]

Will,

The information I have so far is that: 1) You obtained a good frequency 
reading from TP2 during the BFO range test (which says your counter 
probe is probably working). 2) You do not have a good frequency reading 
at TP3 for the PLL Range test - and your results usually indicate that 
the PLL reference oscillator is not oscillating.

There *is* an off chance that the counter probe is working fine at the 
lower BFO frequency, but not at the higher PLL frequency.  If you have 
access to an external frequency counter, you can check the frequency at 
TP3 with that meter as a double check.

Forget the thermistor board for a while - it may be a problem, but even 
if it has a problem, it will not cause the reference oscillator to cease 
oscillation.

Check L33 and the crystal leads for good soldering.  Be certain D18 and 
Q19 are oriented correctly and well soldered.  Check the varactors D16 
and D17 for proper orientation, proper types (D16 large and D17 smaller) 
and good soldering.  Measure the resistance from Q19 source to ground - 
if it is much larger than 270 ohms, check the lead tinning on RFC14 
(remove it and re-tin the leads), and check R21, C84, and C85 for 
correct values as well as good soldering.

If all that above is correct, you should find a frequency near 12100 MHz 
at TP3 - in fact if you find a frequency anywhere between 11,900 and 
12,200, at least the PLL reference is oscillating, but if the range test 
is not within the correct range, you have another problem to be discovered.

73,
Don W3FPR

sbm at ottix.net wrote:
>
> Hi all,
>     I'm part way done building #6197, arriving at the Alignment and 
> Test, Part II of the RF aasembly on page 63 (Rev G of the K2 manual).
>
>     At step 3, I plug-in the probe as described and enter CAL FCTR to 
> enable the on-board counter.  I'm getting a reading of 189.52, rapidly 
> changing by around +/- 0.30.  This doesn't look anything at all like 
> what I should be expecting according to step 3.
>
>     I have pulled the assembly apart, retraced parts placement and 
> connections, and aside from correcting RFC14's winding (just one turn 
> of wire too many), I've not gotten any change in counter reading.  I 
> also re-did the thermistor board just in case, as it was sitting a bit 
> askew and almost making contact with RFC14's toroid core.  Power up 
> and test yielded the same result.
>
>     All else up to this point, including the 4MHz calibration (using a 
> Sony IC-SW7600G for zero-beat), checks out fine.  Also, as posted in a 
> very recent message referring to a PLL range test filaure, I have 
> checked RP2, D16, D17 and R19 for proper values and orientation, as 
> well as for cold solder joints.
>
>     The silver lining in all of this is that I did try the first few 
> steps of the BFO test on page 65 and that turned out perfect.
>
>     Otherwise, I'm pretty much stuck at this point as to where to go 
> from here.  Any pointers appreciated.
>
> Thanks,
>
> Will
> _______________________________________________
> Elecraft mailing list
> Post to: Elecraft at mailman.qth.net
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft   
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>
>