[Elecraft] K2 VCO Alignment Issue
John Wingard
jwin1048 at gmail.com
Tue Apr 30 15:49:07 EDT 2019
Hi Don,
No problem on the delay. OK, after removing 1 turn from T5, the freq. at
TP1 (at 4000) is now 8535.14, so it did come up from the previous value,
but clearly not enough. I have 4.19 V on pin 5 of U6 and I have 4.21 V on
pin 13 of U4.
I wasn't sure of your schedule so I also put in a support request to
Elecraft but have not received a reply as of yet. Hopefully between your
help and their help I can get this resolved.
73 de John, WB4GLJ
On Tue, Apr 30, 2019 at 2:48 PM Don Wilhelm <donwilh at embarqmail.com> wrote:
> 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 <donwilh at embarqmail.com
> > <mailto:donwilh at embarqmail.com>> 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
> > <donwilh at embarqmail.com <mailto:donwilh at embarqmail.com>
> > > <mailto:donwilh at embarqmail.com <mailto:donwilh at embarqmail.com>>>
> > 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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