[Elecraft] PLL reference oscillator range test

[Don Wilhelm]

Mike,

Back up to the PLL range test done with the probe at TP3.  You results there
were incorrect, so everything that follows (VCO voltages etc.) will be
incorrect too.  Get that problem fixed first (yes, there is a proper order
and sequence to those steps in the manual).

The most likely place for a problem to occur in the PLL area is a solder
bridge on the thermistor board.  You may be able to examine it by removing
the front panel and the control board - if not, then the next best thing is
to remove it, check it, solder on new wires and remount it.

One of the quick checks on the health of the thermistor board is to measure
the voltage at U6 pin 5 - if it is not close to 4 volts, then you for sure
have a problem on the thermistor board to correct.

Another strong possibility since you can sometimes get a high and a low
value from your readings is a bad solder connection.  Check the soldering at
R19, RP2, L31, D16 and D17.  Be certain you have the correct varactors at
D16 and D17.

While you attempt the PLL range test, monitor the voltage out of U6 pin 1 -
it should go to almost 8 volts when you tap BAND+ and should drop to near
zero when you tap BAND-.  If you do not see that voltage swing with BAND+/-
then the thermistor board is the most likely place to find the root of your
problem.

Check soldering, then re-check the soldering, and when that is complete,
check the soldering.

73,
Don W3FPR


> -----Original Message-----

> I am assembling my K2 (#5286) and am stuck at the PLL reference
> oscillator range test.
>
> In the frequency counter mode with the probe attached to TP3, I
> get a reading of about 12085 kHz.  However, most of the time, the
> reading is unresponsive to the BAND+ and BAND- switches and the
> voltage on U6 pin 1,2, & 3 is 0.  The BAND switches work fine in
> other modes.
>
> Occasionally the BAND switches do respond and the frequency reads
> up to 12093.8 kHz with the voltages on U6 pin 1, 2, & 3 being
> 4.38, 2.38, 2.38 volts respectively.
>
> I have been checking the soldering around U6, U5, Q19, D16, D17,
> and around the area.  Any ideas of where to focus the search?
>
> Thanks very much,
>
> 73
>
> Mike (KC2FJS)
>