K2 PLL Reference Oscillator failure

[Will-69]

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
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[Don Wilhelm-4]

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

[hidden email] 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: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
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> Elecraft web page: http://www.elecraft.com
>
>

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[Will-69]

On Mon, 20 Aug 2007, Don Wilhelm wrote:

> 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

You did it again Don!  That was the hint I needed - all because of RFC14,
which I had recently re-wound.  Since I had re-installed that one part, I
had thought it would be the last thing to create a problem.  Toroids. :-)

We're now on Part III of the alignment and assembling some mini-modules
for the final push to testing.  Thanks very much!

Will
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