Chris,
If your kit was shipped between mid-August 2018 and mid-January 2019,
then the most likely problem is that Q19 should be replaced with a new
J310 from Elecraft.
As for the 7.07 volts from U6A pin 1, that is not necessarily the cause
of the problem (Q19 should oscillate even with almost 8 volts from U6
pin 1) - if it does not, then the problem is Q19.
While waiting for a replacement J310 from Elecraft, try putting a small
value capacitor from the source of Q19 to ground - use 10 to 15pF. Then
measure the PLL Reference oscillator range using the counter probe in
TP3 and entering CAL FCTR in the menu. You should have oscillation at
both the low (BAND-) and high (BAND+) and the frequency of the high end
should be near 12100 kHz.
Another potential problem if the voltage on U5 pin 7 (and as a result U6
pin 1) can be that the /DAC2CS input to U5 pin 3 is always at or near
ground - check for that condition, and if present, find the solder
bridge. That signal line should go to ground as you rotate the VFO, but
otherwise should be at 5 volts. You will need an oscilloscope to see
the negative transitions.
73,
Don W3FPR
On 5/21/2019 12:27 PM, Chris Smith wrote:
Hi,
I've just completed my K2 up to the PLL reference oscillator.
Initially when I assembled it the PLL reference oscillator would not oscillate
at all. No reading on internal counter. I popped it on my external Racal
counter and still dead. After tracing the problem out I found that the voltage
on input to the varactors was pegged at 7.07V which was too high for the
oscillation to carry on. I lifted one end of R19 on the output of U6A and the
thing oscillates fine isolating this to a control voltage problem.
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