John,
Where did the TP1 frequency go after you removed a turn?
It is possible that the VFO frequency is not getting back to U4 pin 4 --
the signal goes from U3 pin 6 thru C62 and then to U4.
Did we verify that U6 pin 5 is near 4 volts? What is the voltage at U4
pin 13?
Sorry to go over things, but I just returned from a few days away and my
memory is not yet focused.
73,,
Don W3FPR
On 4/28/2019 6:00 PM, John Wingard wrote:
Don,
Finally got back to the K2 this afternoon. I have confirmed that T5 is
on the yellow core, with 16 turns through the center on the red and 4
turns on the green. I mentioned earlier that I got all the toroids
from the Toroid Guy, so I felt confident that it was correctly wound.
I checked all the relay pins on K13, K14, and K15 and did not see any
solder bridges on any of them. Next, I pulled T5 and removed one turn
and re-installed. Unfortunately, nothing has changed. I'm still
getting that same 8.37 V at R30. Incidentally, I'm getting the 8.37 V
on either side of R30. Is that normal? I can also pull T5 and wind a
new one with the parts that came with the kit if you think that might
help, but something tells me that the problem lies elsewhere. I also
thought about pulling C72 and replacing it with another one, but
unfortunately there was only one of that value in the kit and I don't
have anything like it it my parts stash. Any new thoughts?
de John, WB4GLJ
On Sat, Apr 27, 2019 at 6:00 PM Don Wilhelm <[email protected]
<mailto:[email protected]>> wrote:
John,
Both frequencies are too low.
You have either too much capacitance or too much inductance in the
VFO.
Count the number of times the red wire goes through the center of
the T5
core - it should be 16.
Check relays K13, K14 and K15 for solder bridges.
Make sure the core of T5 is yellow.
You might have to try removing a turn from T5 if you can find no
other
cause - there have been a few K2s in the long past where the
permeability if the T5 core was higher than expected, and removing 1
turn from T5 corrected things - I have not seen that recently, but
I do
mention it 'just in case'.
If all else fails, you may have to "wind your way" through the relay
connections for the VFO Range Select area using the Relay Table on
the
Schematic Key page as your guide for the paths through the relays.
73,
Don W3FPR
On 4/27/2019 5:37 PM, John Wingard wrote:
> Hi Don,
>
> Thanks for the quick response. I did check C72 again. It is a 271
> value. I then spread the red turns on T5 as far as I could. I'd say
> they cover about 90+% of the toroid. I put the L30 slug at
mid-point
> of travel and measured voltage at R30 and it is still right at 8.37
> V. While there I checked the frequency at TP1 and it was 8247.90,
> which is considerably lower than the 8913 that you expected.
>
> Next I went up to 7100 and measured the voltage at R30. Still
right at
> 8.37 V, no change. Frequency at TP1 @ 7100 was 11558.11.
>
> So, it appears that the frequency at 4000 is not within the
expected
> range, and likely not at 7100 as well. Hope this tells you
something
> because I'm stumped.
> I've got some plans for this evening so I may not get back on it
until
> tomorrow afternoon, but if you've got any more things for me to
try I
> will do them then.
>
> John, WB4GLJ
>
> On Sat, Apr 27, 2019 at 1:57 PM Don Wilhelm
<[email protected] <mailto:[email protected]>
> <mailto:[email protected] <mailto:[email protected]>>>
wrote:
>
> John,
>
> That high voltage is trying to reduce the capacity of the
varactors.
> Which means there is either too much capacity or too much
> inductance in
> the circuit.
>
> Check the value of C72 first - it should be marked "271".
Then set
> the
> L30 slug to about mid-position and spread the red turns of T5
> enough so
> the starting and ending turns are adjacent. What is the
voltage when
> tuned to 4000 kHz? Measure the frequency at TP1 - it should
be near
> 8913 kHz.
>
> Then change to 40 meters - 7100 kHz - What is the R30
voltage and
> what
> is the VFO frequency measured at TP1.
>
> The answer to those questions will help in determining what
to do
> next.
>
> 73,
> Don W3FPR
>
> On 4/27/2019 1:32 PM, John Wingard wrote:
> > Working on my 2nd K2 (S/N 7869) and have run into a
problem with
> the VCO
> > alignment. I'm getting a constant 8.37 V at R30 at 4.000 MHz..
> I cannot
> > change it with the full range of L30. Correct type inductor is
> installed at
> > L30. Dropping the VFO down to 3.500 doesn't change it
either. I
> have gone
> > back through the archives and read just about every post
> concerning this
> > problem but nothing I have tried has made any difference.
I have
> double
> > checked all correct parts placements and orientations,
re-flowed all
> > connections in the quadrant of the board around the VCO
section.
> T5 is
> > wound as per the manual (from the Toroid Guy) and installed
> correctly. I
> > have tried both spreading and compressing the turns on T5 with
> no change
> > either way.
> >
> > Regarding the thermistor board, I have 4.18 V on pin 5 of U6.
> >
> > Test in the previous section were within specs:
> >
> > 4 MHz Oscillator Cal using CAL FCTR was 12099.61 and confirmed
> with an
> > external counter.
> > Range of the PLL reference oscillator: 12099.61 - 12086.01 =
> 13.59 kHz
> > VCO oscillator test: 8162.60 MHz
> >
> > I'm about out of ideas at this point. What should I start
> checking next?
> >
> > Thanks for any help!
> >
> > 73 de John, WB4GLJ
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