[Elecraft] K2 PLL range test SN 05233

[Don Wilhelm]

Dan,

You do have a problem there somewhere.   The initial frequency is much 
higher than expected, so check L31, C84, C85, D16 and D17 as well as the 
soldering on RP2 and R19 before anything else.  Be certain D16 and D17 
are the proper type and are oriented correctly.
 
After that, if the problem is not corrected, we have to investigate to 
find the source. Start at the beginning of the analog portion for the 
PLL frequency control and make the following measurements.
Set the menu to CAL FCTR and monitor the voltage at U5 pin 7 while 
tapping the BAND+ and BAND- buttons alternately.  The voltage should 
change from about 4 volts to about zero volts.  If that happens, the 
digital portion is doing its job, so move on to the next point.  But if 
you get no change, stop because further measurements of the analog 
signals is futile until you get a voltage swing at U5-7.

If all was well, check the next point, U6 pin 1 which should swing from 
about 8 volts to about zero volts.
If all was good so far, check for a voltage swing at RP2 pin 2 or pin 
4.  It should be similar to that at U6 pin 1.
Then if all that was good, check at the cathode of D16 and the cathode 
of D17.  Again, the voltage swing should be similar to that at U6 pin 1.

If the DC voltages are behaving as expected in the tests above when 
BAND+ and BAND- are tapped, then there is something wrong with the PLL 
crystal, L31, C84, or C85 - recheck those very carefully.

Let us know what you find.  If you are familiar with schematics, you may 
want to follow along at those points on the left side of RF Board 
schematic sheet 1.  The PLL Reference oscillator is nothing but a VXO 
circuit tuned by the varactors D16 and D17.

Note, the LED bargraph indication has nothing to do with this problem, 
so ignore that, and focus on the points I mentioned.

73,
Don W3FPR

kf4pob at aol.com wrote:
> I am at the end of part II and have started my alignment procedures. 
> When I got to CAL FCTR the frequency was 12597.91 with a little 
> fluctuation in the .91  The next step was to the PLL reference 
> oscillator range test. When pushing the Band+ or Band- I get no 
> frequency change at all.  I performed the following voltage test with 
> the rig set on 40 meters.
> U6    lead 1   7.6 vdc             U5   Lead 1   4.9 vdc     RP3   
> Lead   1     7.6 vdc
>                2   4.1 vdc                            2   5.0 
> vdc                        2     4.1 vdc
>                3   4.1 vdc                            3   5.0 
> vdc                        3     4.1 vdc
>                4   0.0 vdc                            4   4.9 
> vdc                        4     0.0 vdc
>                5   4.1 vdc                            5   0.0 
> vdc                        5     0.0 vdc
>                6   .67 vdc                            6   2.0 
> vdc                        6     4.2 vdc
>                7   8.3 vdc                            7   4.1 
> vdc                        7     4.2 vdc
>                8   8.3 vdc                            8   4.1 
> vdc                        8     8.3 vdc
>
> One thing I did notice that before I pushed any of the band buttons 
> the bar graph was on +20.
> When I hit Band + or Band - the bar dropped down one led. I don't know 
> if this indicates or points to the problem. I checked and rechecked my 
> soldering and it looks ok.
> Any help on this will be greatly appreciated.
> 73
> Dan
> af4lb
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