VCO Alignment

[Jim K4ZMV]

Hello.

I appreciate the suggestions related to the subject.  What I have found as an anomoly is that pin 7 of U4 is at 4.94vdc, as is pin 1 of U5.  Both of these pins are clocking (CLK) I/O pins for U4 and U5.  A steady 4.94vdc is abnormal.  I also looked more carefully at T5.  The four green wire turns are situated such that there are four red wire turns on the 2-4 side and seven red wire turns on the 1-3 side.  The green and red wires are in the correct holes.  I can find no problems with the thermister nor can I find any soldering problems.  Any suggestions at this point would be appreciated.  The alignment steps up to VCO alignment and the step subsequent all check out perfectly.  Thanks.

73,

Jim,K4ZMV
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
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

[Don Wilhelm-3]

Jim,

If you look at those lines with a 'scope and move the VFO dial, you will
likely see very short negative going pulses.  They are only active when need
be, and will show as almost 5 volts with a DMM.  Those lines are likely not
your problem unless you missed a solder connection on the signal lines on
the control board.

Go back a step to verify things:  Did you get a successful range when you
did the PLL Reference Oscillator test?  The high frequency should be near
12100 kHz and the low should be between 12080 and 12090.  If that range test
was not successful, then you need to start there to find out why.

If the PLL range was correct, then proceed to investigate the VCO.  The
first step is to check the voltage at pin 5 of U2 - if it is anything other
than 4 volts (within 10%), stop and recheck the thermistor board.

Next step is to find out what frequency the VCO is actually oscillating at
for each band.  The counter probe should be in TP1 - set the VFO dial to the
low frequency end of each band in turn and enter the menu to check CAL FCTR.
Compare the frequencies observed with the chart on the lower left corner of
the  K2 Schematic Key page in Appendix B of the manual.

Do the frequency measurements before drawing any conclusions - are all bands
incorrect, or only some?  If all, what are the frequencies?  If some, which
ones and what are the frequencies for each?  There could be an incorrect
capacitor, unsoldered connection, or incorrectly oriented varactor in the
VFO Range Select area that would give you the inability to change the
voltage at the left end of R30.  The absolute limits of the voltage at the
left end of R30 (output of U6 pin 7) are 8 volts and zero volts.  Your
indication that you find only 8 volts says that the VCO frequency is too low
and the PLL chip is attempting to reduce the varactor capacity, but has 'run
out of adjustment' at the high voltage end.  You will have to search for the
reason why.

I have written a lot of words here, but follow the steps in order - if you
find one in th emiddle that is not correct, stop because that has to be
corrected before any of the following are attempted (you can expect only
'wierd' readings beyond that point).

73,
Don W3FPR

> -----Original Message-----
> I appreciate the suggestions related to the subject.  What I have
> found as an anomoly is that pin 7 of U4 is at 4.94vdc, as is pin
> 1 of U5.  Both of these pins are clocking (CLK) I/O pins for U4
> and U5.  A steady 4.94vdc is abnormal.  I also looked more
> carefully at T5.  The four green wire turns are situated such
> that there are four red wire turns on the 2-4 side and seven red
> wire turns on the 1-3 side.  The green and red wires are in the
> correct holes.  I can find no problems with the thermister nor
> can I find any soldering problems.  Any suggestions at this point
> would be appreciated.  The alignment steps up to VCO alignment
> and the step subsequent all check out perfectly.  Thanks.
>
> 73,
>
> Jim,K4ZMV
>

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
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