K2 - Tuning is Nonlinear

[Cox, Norman R.]

Dear Group:


     I am about finished building my K2, but have encountered a frustrating problem.  Maybe someone can help me.   I have performed most of the alignment in Part III, but noticed the following when trying to receive signals:


    When I turn the tuning knob, tuning is nonlinear.  On some bands, it will change frequency gradually, as it should, but then jump to another frequency.  On other bands, it never tunes linear at all, but just makes large jumps in frequency as you are turning the knob.


     I checked this jump, and sure enough, it was 5 KHz.  So the PLL is working ok.  The problem is the lower bits of resolution that are processed by U5 (the DAC) on the RF Board.  On two of the bands, as the knob is turned, the output of U5 (pin 7) varies from 0 to about 0.8 volts, then jumps to 4.0 volts.  On one or two other bands, it just jumps the 5 KHz -- no linear parts.  And on the other bands, the output of the DAC does not change at all that I can tell.


   I checked the output of the encoder, and it seems to be working -- at least, digital levels are sent to the microprocessor U6 on the control board.  I don't know if there's something messed up in the EEPROM or the DAC or the programming of the microprocessor.


   Have any of you had this problem or have suggestions?


Thanks for your assistance,


Norm

KE0ZT

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[Don Wilhelm]

Norman,

I would first re-do the CAL PLL procedure, then see what happens.
If that does not fix it, try doing a Master Reset (hold the 4, 5, and 6
butons in while powering on).  When INFO 201 turns to the frequency
display, do a CAL PLL and check again.

Check the soldering of U5 and Control Board U7 and re-test after a CAL
PLL run.

Lastly, Try adding a 10 to 15pF capacitor between the source of RF Board
Q19 and ground.  Then re-run CAL PLL.

73,
Don W3FPR

On 7/17/2018 9:52 PM, Cox, Norman R. wrote:

> Dear Group:
>
>
>       I am about finished building my K2, but have encountered a frustrating problem.  Maybe someone can help me.   I have performed most of the alignment in Part III, but noticed the following when trying to receive signals:
>
>
>      When I turn the tuning knob, tuning is nonlinear.  On some bands, it will change frequency gradually, as it should, but then jump to another frequency.  On other bands, it never tunes linear at all, but just makes large jumps in frequency as you are turning the knob.
>
>
>       I checked this jump, and sure enough, it was 5 KHz.  So the PLL is working ok.  The problem is the lower bits of resolution that are processed by U5 (the DAC) on the RF Board.  On two of the bands, as the knob is turned, the output of U5 (pin 7) varies from 0 to about 0.8 volts, then jumps to 4.0 volts.  On one or two other bands, it just jumps the 5 KHz -- no linear parts.  And on the other bands, the output of the DAC does not change at all that I can tell.

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