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K2 7747 VCO alignment problem

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Keith Hamilton

K2 7747 VCO alignment problem

I am having trouble with the K2 VCO alignment. I have moved the T5 windings
and obtained 6 volts at the left end of R30. I then went on to the chart
(table 6-1) to measure the voltages at the listed frequencies. My readings
are ok on 80 40 and 15 meters (between 1.5 to 7.5 volts) but on 30,20,17
,12 and 10 meters the voltage is 8.29 volts and does not change.

I have checked the solder connections of T5 and the value of C72 (271). The
diodes D21,D22,D23, D24, D25 and D26 are correctly installed. I also went
over the solder connections of K13, K14 and K15.

Now I'm stuck. Any help will be appreciated.

Keioth Hamilton N8CEP
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Dave Van Wallaghen-2

Re: K2 7747 VCO alignment problem

Hi Keith,

Were you able to get 6v on R30 by tuning L30? Did you have to bring the
voltage down or up by moving the windings on T5?

If you would, set the VFO to 4 MHz and do a CAL FCTR on TP1 and let me
know what the reading is. I'm just looking for a couple of clues before
we proceed.

73,
Dave, W8FGU

On 7/13/2020 2:52:11 PM, "Keith Hamilton" <[hidden email]> wrote:

>I am having trouble with the K2 VCO alignment. I have moved the T5 windings
>and obtained 6 volts at the left end of R30. I then went on to the chart
>(table 6-1) to measure the voltages at the listed frequencies. My readings
>are ok on 80 40 and 15 meters (between 1.5 to 7.5 volts) but on 30,20,17
>,12 and 10 meters the voltage is 8.29 volts and does not change.
>
>I have checked the solder connections of T5 and the value of C72 (271). The
>diodes D21,D22,D23, D24, D25 and D26 are correctly installed. I also went
>over the solder connections of K13, K14 and K15.
>
>Now I'm stuck. Any help will be appreciated.
>
>Keioth Hamilton N8CEP
>______________________________________________________________
>Elecraft mailing list
>Home: http://mailman.qth.net/mailman/listinfo/elecraft
>Help: http://mailman.qth.net/mmfaq.htm
>Post: mailto:[hidden email]
>
>This list hosted by: http://www.qsl.net
>Please help support this email list: http://www.qsl.net/donate.html
>Message delivered to [hidden email]

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

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Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

Keith Hamilton

Re: K2 7747 VCO alignment problem

Thanks for your help Dave!

Yes. I was able to get 6 volts on R30 by turning L30. At first the voltage
was too high
so I adjusted the turns on T5 by spreading the red windings further apart.
Then I
was able to get to 6 volts.

I did a CAL FCTR with the probe on TP1 and the frequency set to 4000,
The reading is 8912.22

73 Keith N8CEP

On Mon, Jul 13, 2020 at 3:59 PM Dave Van Wallaghen <[hidden email]> wrote:

> Hi Keith,
>
> Were you able to get 6v on R30 by tuning L30? Did you have to bring the
> voltage down or up by moving the windings on T5?
>
> If you would, set the VFO to 4 MHz and do a CAL FCTR on TP1 and let me
> know what the reading is. I'm just looking for a couple of clues before
> we proceed.
>
> 73,
> Dave, W8FGU
>
>
> On 7/13/2020 2:52:11 PM, "Keith Hamilton" <[hidden email]> wrote:
>
> >I am having trouble with the K2 VCO alignment. I have moved the T5
> windings
> >and obtained 6 volts at the left end of R30. I then went on to the chart
> >(table 6-1) to measure the voltages at the listed frequencies. My readings
> >are ok on 80 40 and 15 meters (between 1.5 to 7.5 volts) but on 30,20,17
> >,12 and 10 meters the voltage is 8.29 volts and does not change.
> >
> >I have checked the solder connections of T5 and the value of C72 (271).
> The
> >diodes D21,D22,D23, D24, D25 and D26 are correctly installed. I also went
> >over the solder connections of K13, K14 and K15.
> >
> >Now I'm stuck. Any help will be appreciated.
> >
> >Keioth Hamilton N8CEP
> >______________________________________________________________
> >Elecraft mailing list
> >Home: http://mailman.qth.net/mailman/listinfo/elecraft
> >Help: http://mailman.qth.net/mmfaq.htm
> >Post: mailto:[hidden email]
> >
> >This list hosted by: http://www.qsl.net
> >Please help support this email list: http://www.qsl.net/donate.html
> >Message delivered to [hidden email]
>
>

Don Wilhelm

Re: K2 7747 VCO alignment problem

In reply to this post by Keith Hamilton

Keith,

Not a nice problem to address. I can give you some troubleshooting
information if you are willing to hang in there with me.
Eliminate the "[Elecraft]" from the subject line and reply to me
directly (not to the list).

Relay K15 is common on all those bands, but not on 80 and 40m, but that
does not explain why 15 meters is OK.
Check the resistance between pins 1 and 10 of all 3 relays - that is the
coil resistance, and if I recall, it is about 235 ohms.

Check that C73 and C74 are the correct values.

If that does not reveal the problem, you will have to measure the
open/closed state of the relays for the next step. Can you find those
relays on the schematic? They are all shown in the reset state.

73,
Don W3FPR

On 7/13/2020 2:52 PM, Keith Hamilton wrote:

Keith Hamilton

Fwd: Re[2]: K2 7747 VCO alignment problem

In reply to this post by Keith Hamilton

---------- Forwarded message ---------
From: Keith Hamilton <[hidden email]>
Date: Mon, Jul 13, 2020 at 9:19 PM
Subject: Re: Re[2]: [Elecraft] K2 7747 VCO alignment problem
To: Dave Van Wallaghen <[hidden email]>

Dave

Yes the frequency changes when turning the VFO knob when measuring with CAL
FCTR on TP1.

I have checked the markings on C71, C72, C73, and C74 (C75 is not installed
yet). They are
all correct and I resoldered them to be sure.

I am beginning to think I might have a bad relay K13, K14 or K15. My good
bands are 80,40 and
15 meters. My bad bands are 30,20,17,12 and 10 meters. Looking at the relay
table in appendix B
I am not sure which relay could be bad. How can I test them? Should I try
to replace them?
73,
Keith N8CEP

On Mon, Jul 13, 2020 at 4:58 PM Dave Van Wallaghen <[hidden email]> wrote:

> Ok Keith, just to make sure things are where we want on the bands that
> seem to work, does the frequency change when turning the VFO knob when
> measuring with CAL FCTR on TP1? If they do, then things are working ok.
>
> For the bands that are locked at 8.28v, that is the max output from the
> integrator circuit (U6B). This means that there is no lock between the PLL
> Oscillator and the VCO circuit and the PLL chip (U4) is trying to drive the
> varactors to provide more capacitance to the VCO circuit. The most likely
> cause will be a misplaced capacitor in the VCO range selector (C71 - C75)
> or a problem in the VCO circuit itself. But because this may be band
> dependent, I would look first in that range selection circuit. Verify that
> those caps are the proper values. They are easily misread and will cause
> the type of thing you are seeing.
>
> Also verify those varactor diodes are the proper type and in the right
> places. Soldering issues are typically the leading cause of problems, so
> check that also. If all looks right to you, you may want to signal trace
> through that selection circuit to verify the proper relays and active for
> the bands not working. There is a relay table in Appendix B that shows you
> which relays are active for each band.
>
> This is a brand new build, correct?
>
> 73,
> Dave, W8FGU
>
>
> On 7/13/2020 4:41:07 PM, "Keith Hamilton" <[hidden email]> wrote:
>
> Thanks for your help Dave!
>
> Yes. I was able to get 6 volts on R30 by turning L30. At first the voltage
> was too high
> so I adjusted the turns on T5 by spreading the red windings further apart.
> Then I
> was able to get to 6 volts.
>
> I did a CAL FCTR with the probe on TP1 and the frequency set to 4000,
> The reading is 8912.22
>
> 73 Keith N8CEP
>
>
> On Mon, Jul 13, 2020 at 3:59 PM Dave Van Wallaghen <[hidden email]> wrote:
>
>> Hi Keith,
>>
>> Were you able to get 6v on R30 by tuning L30? Did you have to bring the
>> voltage down or up by moving the windings on T5?
>>
>> If you would, set the VFO to 4 MHz and do a CAL FCTR on TP1 and let me
>> know what the reading is. I'm just looking for a couple of clues before
>> we proceed.
>>
>> 73,
>> Dave, W8FGU
>>
>>
>> On 7/13/2020 2:52:11 PM, "Keith Hamilton" <[hidden email]> wrote:
>>
>> >I am having trouble with the K2 VCO alignment. I have moved the T5
>> windings
>> >and obtained 6 volts at the left end of R30. I then went on to the chart
>> >(table 6-1) to measure the voltages at the listed frequencies. My
>> readings
>> >are ok on 80 40 and 15 meters (between 1.5 to 7.5 volts) but on 30,20,17
>> >,12 and 10 meters the voltage is 8.29 volts and does not change.
>> >
>> >I have checked the solder connections of T5 and the value of C72 (271).
>> The
>> >diodes D21,D22,D23, D24, D25 and D26 are correctly installed. I also went
>> >over the solder connections of K13, K14 and K15.
>> >
>> >Now I'm stuck. Any help will be appreciated.
>> >
>> >Keioth Hamilton N8CEP
>> >______________________________________________________________
>> >Elecraft mailing list
>> >Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> >Help: http://mailman.qth.net/mmfaq.htm
>> >Post: mailto:[hidden email]
>> >
>> >This list hosted by: http://www.qsl.net
>> >Please help support this email list: http://www.qsl.net/donate.html
>> >Message delivered to [hidden email]
>>
>>

Dave Van Wallaghen-2

Re: Fwd: Re[2]: K2 7747 VCO alignment problem

Keith,

I saw Don respond to this and he is right that K15 would be the common
denominator if not for 15m. You can check to see if the coils are intact
if you measure the resistance between pins 1 and 10 for each. It should
be around 230 ohms or so. If you find one open or well away from that
resistance, then it would indicate a bad coil on that relay.

You can also measure the intended path through the relays for each band
and make sure there are no unintended paths. If you can read the
schematic, it shows the path with each relay in it's reset state. You
would need to consult the table in Appendix B to see which relay(s) are
active for a respective band and you can then measure the continuity of
the intended path. You should also check any unintended paths which
could indicate a problem.

As Don stated, this is not a fun problem to find and will take some good
debugging skills. So far, everything you've indicated seems to suggest
the PLL oscillator and VCO circuits are working properly, but the range
selection area is not producing the proper capacitance to allow the VCO
to produce the proper frequency on those bands you indicated.

If reading the schematic is a problem, let us know and I am sure between
Don and myself, we can give you some step by step instructions for
tracing through this problem.

73,
Dave W8FGU

------ Original Message ------
From: "Keith Hamilton" <[hidden email]>
To: [hidden email]
Sent: 7/13/2020 9:34:03 PM
Subject: [Elecraft] Fwd: Re[2]: K2 7747 VCO alignment problem

>---------- Forwarded message ---------
>From: Keith Hamilton <[hidden email]>
>Date: Mon, Jul 13, 2020 at 9:19 PM
>Subject: Re: Re[2]: [Elecraft] K2 7747 VCO alignment problem
>To: Dave Van Wallaghen <[hidden email]>
>
>
>Dave
>
>Yes the frequency changes when turning the VFO knob when measuring with CAL
>FCTR on TP1.
>
>I have checked the markings on C71, C72, C73, and C74 (C75 is not installed
>yet). They are
>all correct and I resoldered them to be sure.
>
>I am beginning to think I might have a bad relay K13, K14 or K15. My good
>bands are 80,40 and
>15 meters. My bad bands are 30,20,17,12 and 10 meters. Looking at the relay
>table in appendix B
>I am not sure which relay could be bad. How can I test them? Should I try
>to replace them?
>73,
>Keith N8CEP
>
>
>On Mon, Jul 13, 2020 at 4:58 PM Dave Van Wallaghen <[hidden email]> wrote:
>
>> Ok Keith, just to make sure things are where we want on the bands that
>> seem to work, does the frequency change when turning the VFO knob when
>> measuring with CAL FCTR on TP1? If they do, then things are working ok.
>>
>> For the bands that are locked at 8.28v, that is the max output from the
>> integrator circuit (U6B). This means that there is no lock between the PLL
>> Oscillator and the VCO circuit and the PLL chip (U4) is trying to drive the
>> varactors to provide more capacitance to the VCO circuit. The most likely
>> cause will be a misplaced capacitor in the VCO range selector (C71 - C75)
>> or a problem in the VCO circuit itself. But because this may be band
>> dependent, I would look first in that range selection circuit. Verify that
>> those caps are the proper values. They are easily misread and will cause
>> the type of thing you are seeing.
>>
>> Also verify those varactor diodes are the proper type and in the right
>> places. Soldering issues are typically the leading cause of problems, so
>> check that also. If all looks right to you, you may want to signal trace
>> through that selection circuit to verify the proper relays and active for
>> the bands not working. There is a relay table in Appendix B that shows you
>> which relays are active for each band.
>>
>> This is a brand new build, correct?
>>
>> 73,
>> Dave, W8FGU
>>
>>
>> On 7/13/2020 4:41:07 PM, "Keith Hamilton" <[hidden email]> wrote:
>>
>> Thanks for your help Dave!
>>
>> Yes. I was able to get 6 volts on R30 by turning L30. At first the voltage
>> was too high
>> so I adjusted the turns on T5 by spreading the red windings further apart.
>> Then I
>> was able to get to 6 volts.
>>
>> I did a CAL FCTR with the probe on TP1 and the frequency set to 4000,
>> The reading is 8912.22
>>
>> 73 Keith N8CEP
>>
>>
>> On Mon, Jul 13, 2020 at 3:59 PM Dave Van Wallaghen <[hidden email]> wrote:
>>
>>> Hi Keith,
>>>
>>> Were you able to get 6v on R30 by tuning L30? Did you have to bring the
>>> voltage down or up by moving the windings on T5?
>>>
>>> If you would, set the VFO to 4 MHz and do a CAL FCTR on TP1 and let me
>>> know what the reading is. I'm just looking for a couple of clues before
>>> we proceed.
>>>
>>> 73,
>>> Dave, W8FGU
>>>
>>>
>>> On 7/13/2020 2:52:11 PM, "Keith Hamilton" <[hidden email]> wrote:
>>>
>>> >I am having trouble with the K2 VCO alignment. I have moved the T5
>>> windings
>>> >and obtained 6 volts at the left end of R30. I then went on to the chart
>>> >(table 6-1) to measure the voltages at the listed frequencies. My
>>> readings
>>> >are ok on 80 40 and 15 meters (between 1.5 to 7.5 volts) but on 30,20,17
>>> >,12 and 10 meters the voltage is 8.29 volts and does not change.
>>> >
>>> >I have checked the solder connections of T5 and the value of C72 (271).
>>> The
>>> >diodes D21,D22,D23, D24, D25 and D26 are correctly installed. I also went
>>> >over the solder connections of K13, K14 and K15.
>>> >
>>> >Now I'm stuck. Any help will be appreciated.
>>> >
>>> >Keioth Hamilton N8CEP
>>> >______________________________________________________________
>>> >Elecraft mailing list
>>> >Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>> >Help: http://mailman.qth.net/mmfaq.htm
>>> >Post: mailto:[hidden email]
>>> >
>>> >This list hosted by: http://www.qsl.net
>>> >Please help support this email list: http://www.qsl.net/donate.html
>>> >Message delivered to [hidden email]
>>>
>>>
>______________________________________________________________
>Elecraft mailing list
>Home: http://mailman.qth.net/mailman/listinfo/elecraft
>Help: http://mailman.qth.net/mmfaq.htm
>Post: mailto:[hidden email]
>
>This list hosted by: http://www.qsl.net
>Please help support this email list: http://www.qsl.net/donate.html
>Message delivered to [hidden email]

Keith Hamilton

Re: Fwd: Re[2]: K2 7747 VCO alignment problem

OK Dave -

I will check the relays as you suggest. In troubleshooting capacitors I
messed up
C74. I pulled it off the board and sent a request to Elecraft for a
replacement.
That may solve the problem. In the meantime I will check the coils on the
K13 to K15
relays and let you know what I find.

I did not see Don's post. I will check it out. So I will be waiting a bit
to fix this problem,

73 and thanks!
Keith N8CEP

On Mon, Jul 13, 2020 at 10:36 PM Dave Van Wallaghen <[hidden email]> wrote:

> Keith,
>
> I saw Don respond to this and he is right that K15 would be the common
> denominator if not for 15m. You can check to see if the coils are intact
> if you measure the resistance between pins 1 and 10 for each. It should
> be around 230 ohms or so. If you find one open or well away from that
> resistance, then it would indicate a bad coil on that relay.
>
> You can also measure the intended path through the relays for each band
> and make sure there are no unintended paths. If you can read the
> schematic, it shows the path with each relay in it's reset state. You
> would need to consult the table in Appendix B to see which relay(s) are
> active for a respective band and you can then measure the continuity of
> the intended path. You should also check any unintended paths which
> could indicate a problem.
>
> As Don stated, this is not a fun problem to find and will take some good
> debugging skills. So far, everything you've indicated seems to suggest
> the PLL oscillator and VCO circuits are working properly, but the range
> selection area is not producing the proper capacitance to allow the VCO
> to produce the proper frequency on those bands you indicated.
>
> If reading the schematic is a problem, let us know and I am sure between
> Don and myself, we can give you some step by step instructions for
> tracing through this problem.
>
> 73,
> Dave W8FGU
>
> ------ Original Message ------
> From: "Keith Hamilton" <[hidden email]>
> To: [hidden email]
> Sent: 7/13/2020 9:34:03 PM
> Subject: [Elecraft] Fwd: Re[2]: K2 7747 VCO alignment problem
>
> >---------- Forwarded message ---------
> >From: Keith Hamilton <[hidden email]>
> >Date: Mon, Jul 13, 2020 at 9:19 PM
> >Subject: Re: Re[2]: [Elecraft] K2 7747 VCO alignment problem
> >To: Dave Van Wallaghen <[hidden email]>
> >
> >
> >Dave
> >
> >Yes the frequency changes when turning the VFO knob when measuring with
> CAL
> >FCTR on TP1.
> >
> >I have checked the markings on C71, C72, C73, and C74 (C75 is not
> installed
> >yet). They are
> >all correct and I resoldered them to be sure.
> >
> >I am beginning to think I might have a bad relay K13, K14 or K15. My good
> >bands are 80,40 and
> >15 meters. My bad bands are 30,20,17,12 and 10 meters. Looking at the
> relay
> >table in appendix B
> >I am not sure which relay could be bad. How can I test them? Should I try
> >to replace them?
> >73,
> >Keith N8CEP
> >
> >
> >On Mon, Jul 13, 2020 at 4:58 PM Dave Van Wallaghen <[hidden email]>
> wrote:
> >
> >> Ok Keith, just to make sure things are where we want on the bands that
> >> seem to work, does the frequency change when turning the VFO knob when
> >> measuring with CAL FCTR on TP1? If they do, then things are working ok.
> >>
> >> For the bands that are locked at 8.28v, that is the max output from the
> >> integrator circuit (U6B). This means that there is no lock between the
> PLL
> >> Oscillator and the VCO circuit and the PLL chip (U4) is trying to
> drive the
> >> varactors to provide more capacitance to the VCO circuit. The most
> likely
> >> cause will be a misplaced capacitor in the VCO range selector (C71 -
> C75)
> >> or a problem in the VCO circuit itself. But because this may be band
> >> dependent, I would look first in that range selection circuit. Verify
> that
> >> those caps are the proper values. They are easily misread and will
> cause
> >> the type of thing you are seeing.
> >>
> >> Also verify those varactor diodes are the proper type and in the right
> >> places. Soldering issues are typically the leading cause of problems,
> so
> >> check that also. If all looks right to you, you may want to signal
> trace
> >> through that selection circuit to verify the proper relays and active
> for
> >> the bands not working. There is a relay table in Appendix B that shows
> you
> >> which relays are active for each band.
> >>
> >> This is a brand new build, correct?
> >>
> >> 73,
> >> Dave, W8FGU
> >>
> >>
> >> On 7/13/2020 4:41:07 PM, "Keith Hamilton" <[hidden email]>
> wrote:
> >>
> >> Thanks for your help Dave!
> >>
> >> Yes. I was able to get 6 volts on R30 by turning L30. At first the
> voltage
> >> was too high
> >> so I adjusted the turns on T5 by spreading the red windings further
> apart.
> >> Then I
> >> was able to get to 6 volts.
> >>
> >> I did a CAL FCTR with the probe on TP1 and the frequency set to 4000,
> >> The reading is 8912.22
> >>
> >> 73 Keith N8CEP
> >>
> >>
> >> On Mon, Jul 13, 2020 at 3:59 PM Dave Van Wallaghen <[hidden email]>
> wrote:
> >>
> >>> Hi Keith,
> >>>
> >>> Were you able to get 6v on R30 by tuning L30? Did you have to bring
> the
> >>> voltage down or up by moving the windings on T5?
> >>>
> >>> If you would, set the VFO to 4 MHz and do a CAL FCTR on TP1 and let me
> >>> know what the reading is. I'm just looking for a couple of clues
> before
> >>> we proceed.
> >>>
> >>> 73,
> >>> Dave, W8FGU
> >>>
> >>>
> >>> On 7/13/2020 2:52:11 PM, "Keith Hamilton" <[hidden email]>
> wrote:
> >>>
> >>> >I am having trouble with the K2 VCO alignment. I have moved the T5
> >>> windings
> >>> >and obtained 6 volts at the left end of R30. I then went on to the
> chart
> >>> >(table 6-1) to measure the voltages at the listed frequencies. My
> >>> readings
> >>> >are ok on 80 40 and 15 meters (between 1.5 to 7.5 volts) but on
> 30,20,17
> >>> >,12 and 10 meters the voltage is 8.29 volts and does not change.
> >>> >
> >>> >I have checked the solder connections of T5 and the value of C72
> (271).
> >>> The
> >>> >diodes D21,D22,D23, D24, D25 and D26 are correctly installed. I also
> went
> >>> >over the solder connections of K13, K14 and K15.
> >>> >
> >>> >Now I'm stuck. Any help will be appreciated.
> >>> >
> >>> >Keioth Hamilton N8CEP
> >>> >______________________________________________________________
> >>> >Elecraft mailing list
> >>> >Home: http://mailman.qth.net/mailman/listinfo/elecraft
> >>> >Help: http://mailman.qth.net/mmfaq.htm
> >>> >Post: mailto:[hidden email]
> >>> >
> >>> >This list hosted by: http://www.qsl.net
> >>> >Please help support this email list: http://www.qsl.net/donate.html
> >>> >Message delivered to [hidden email]
> >>>
> >>>
> >______________________________________________________________
> >Elecraft mailing list
> >Home: http://mailman.qth.net/mailman/listinfo/elecraft
> >Help: http://mailman.qth.net/mmfaq.htm
> >Post: mailto:[hidden email]
> >
> >This list hosted by: http://www.qsl.net
> >Please help support this email list: http://www.qsl.net/donate.html
> >Message delivered to [hidden email]
>
>

Don Wilhelm

Re: Fwd: Re[2]: K2 7747 VCO alignment problem

Keith,

C74 could explain a problem on 30, 20, and 12 meters, but you apparently
have something else awry.

If you do not find a problem with the relay coils, you should next check
the contacts of relays K13, K14 and K15.
On 20 meters, all the relays should be set - meaning you should have
conductivity from pins 3 to 4 and not between pins 2 and 3.
Check the other side of the relays - conductivity between pins 7 and 8,
and open between pins 8 and 9

Then check 80 meters, only K13 should be set - so check K14 and K15
which are reset on that band - no conductivity between pins 4 and 3 and
open between pins 2 and 3
Also check the other side, conductivity between pins 8 and 9 and open
between 7 and 8.

Then switch to 30 meters and you can check the reset state of K13 -
Continuity between pins 2 and 3 and open between pins 3 and 4
Also conductivity between pins 8 and 9 and open between pins 7 and 8.

If all that checks out, look again at the capacitor values of C71, C72,
and C73. I know some of those capacitors are tight tucked between the
relays, but bend them over a bit and use a good light and possibly a
magnifier to read the markings.

73,
Don W3FPR

On 7/13/2020 11:00 PM, Keith Hamilton wrote:

> OK Dave -
>
> I will check the relays as you suggest. In troubleshooting capacitors I
> messed up
> C74. I pulled it off the board and sent a request to Elecraft for a
> replacement.
> That may solve the problem. In the meantime I will check the coils on the
> K13 to K15
> relays and let you know what I find.
>
> I did not see Don's post. I will check it out. So I will be waiting a bit
> to fix this problem,
>
> 73 and thanks!
> Keith N8CEP
>
> On Mon, Jul 13, 2020 at 10:36 PM Dave Van Wallaghen <[hidden email]> wrote:
>
>> Keith,
>>
>> I saw Don respond to this and he is right that K15 would be the common
>> denominator if not for 15m. You can check to see if the coils are intact
>> if you measure the resistance between pins 1 and 10 for each. It should
>> be around 230 ohms or so. If you find one open or well away from that
>> resistance, then it would indicate a bad coil on that relay.
>>
>> You can also measure the intended path through the relays for each band
>> and make sure there are no unintended paths. If you can read the
>> schematic, it shows the path with each relay in it's reset state. You
>> would need to consult the table in Appendix B to see which relay(s) are
>> active for a respective band and you can then measure the continuity of
>> the intended path. You should also check any unintended paths which
>> could indicate a problem.
>>
>> As Don stated, this is not a fun problem to find and will take some good
>> debugging skills. So far, everything you've indicated seems to suggest
>> the PLL oscillator and VCO circuits are working properly, but the range
>> selection area is not producing the proper capacitance to allow the VCO
>> to produce the proper frequency on those bands you indicated.
>>
>> If reading the schematic is a problem, let us know and I am sure between
>> Don and myself, we can give you some step by step instructions for
>> tracing through this problem.
>>
>> 73,
>> Dave W8FGU
>>
>> ------ Original Message ------
>> From: "Keith Hamilton" <[hidden email]>
>> To: [hidden email]
>> Sent: 7/13/2020 9:34:03 PM
>> Subject: [Elecraft] Fwd: Re[2]: K2 7747 VCO alignment problem
>>
>>> ---------- Forwarded message ---------
>>> From: Keith Hamilton <[hidden email]>
>>> Date: Mon, Jul 13, 2020 at 9:19 PM
>>> Subject: Re: Re[2]: [Elecraft] K2 7747 VCO alignment problem
>>> To: Dave Van Wallaghen <[hidden email]>
>>>
>>>
>>> Dave
>>>
>>> Yes the frequency changes when turning the VFO knob when measuring with
>> CAL
>>> FCTR on TP1.
>>>
>>> I have checked the markings on C71, C72, C73, and C74 (C75 is not
>> installed
>>> yet). They are
>>> all correct and I resoldered them to be sure.
>>>
>>> I am beginning to think I might have a bad relay K13, K14 or K15. My good
>>> bands are 80,40 and
>>> 15 meters. My bad bands are 30,20,17,12 and 10 meters. Looking at the
>> relay
>>> table in appendix B
>>> I am not sure which relay could be bad. How can I test them? Should I try
>>> to replace them?
>>> 73,
>>> Keith N8CEP
>>>
>>>
>>> On Mon, Jul 13, 2020 at 4:58 PM Dave Van Wallaghen <[hidden email]>
>> wrote:
>>>
>>>> Ok Keith, just to make sure things are where we want on the bands that
>>>> seem to work, does the frequency change when turning the VFO knob when
>>>> measuring with CAL FCTR on TP1? If they do, then things are working ok.
>>>>
>>>> For the bands that are locked at 8.28v, that is the max output from the
>>>> integrator circuit (U6B). This means that there is no lock between the
>> PLL
>>>> Oscillator and the VCO circuit and the PLL chip (U4) is trying to
>> drive the
>>>> varactors to provide more capacitance to the VCO circuit. The most
>> likely
>>>> cause will be a misplaced capacitor in the VCO range selector (C71 -
>> C75)
>>>> or a problem in the VCO circuit itself. But because this may be band
>>>> dependent, I would look first in that range selection circuit. Verify
>> that
>>>> those caps are the proper values. They are easily misread and will
>> cause
>>>> the type of thing you are seeing.
>>>>
>>>> Also verify those varactor diodes are the proper type and in the right
>>>> places. Soldering issues are typically the leading cause of problems,
>> so
>>>> check that also. If all looks right to you, you may want to signal
>> trace
>>>> through that selection circuit to verify the proper relays and active
>> for
>>>> the bands not working. There is a relay table in Appendix B that shows
>> you
>>>> which relays are active for each band.
>>>>
>>>> This is a brand new build, correct?
>>>>
>>>> 73,
>>>> Dave, W8FGU
>>>>
>>>>
>>>> On 7/13/2020 4:41:07 PM, "Keith Hamilton" <[hidden email]>
>> wrote:
>>>>
>>>> Thanks for your help Dave!
>>>>
>>>> Yes. I was able to get 6 volts on R30 by turning L30. At first the
>> voltage
>>>> was too high
>>>> so I adjusted the turns on T5 by spreading the red windings further
>> apart.
>>>> Then I
>>>> was able to get to 6 volts.
>>>>
>>>> I did a CAL FCTR with the probe on TP1 and the frequency set to 4000,
>>>> The reading is 8912.22
>>>>
>>>> 73 Keith N8CEP
>>>>
>>>>
>>>> On Mon, Jul 13, 2020 at 3:59 PM Dave Van Wallaghen <[hidden email]>
>> wrote:
>>>>
>>>>> Hi Keith,
>>>>>
>>>>> Were you able to get 6v on R30 by tuning L30? Did you have to bring
>> the
>>>>> voltage down or up by moving the windings on T5?
>>>>>
>>>>> If you would, set the VFO to 4 MHz and do a CAL FCTR on TP1 and let me
>>>>> know what the reading is. I'm just looking for a couple of clues
>> before
>>>>> we proceed.
>>>>>
>>>>> 73,
>>>>> Dave, W8FGU
>>>>>
>>>>>
>>>>> On 7/13/2020 2:52:11 PM, "Keith Hamilton" <[hidden email]>
>> wrote:
>>>>>
>>>>> >I am having trouble with the K2 VCO alignment. I have moved the T5
>>>>> windings
>>>>> >and obtained 6 volts at the left end of R30. I then went on to the
>> chart
>>>>> >(table 6-1) to measure the voltages at the listed frequencies. My
>>>>> readings
>>>>> >are ok on 80 40 and 15 meters (between 1.5 to 7.5 volts) but on
>> 30,20,17
>>>>> >,12 and 10 meters the voltage is 8.29 volts and does not change.
>>>>> >
>>>>> >I have checked the solder connections of T5 and the value of C72
>> (271).
>>>>> The
>>>>> >diodes D21,D22,D23, D24, D25 and D26 are correctly installed. I also
>> went
>>>>> >over the solder connections of K13, K14 and K15.
>>>>> >
>>>>> >Now I'm stuck. Any help will be appreciated.
>>>>> >
>>>>> >Keioth Hamilton N8CEP
>>>>> >______________________________________________________________
>>>>> >Elecraft mailing list
>>>>> >Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>>>> >Help: http://mailman.qth.net/mmfaq.htm
>>>>> >Post: mailto:[hidden email]
>>>>> >
>>>>> >This list hosted by: http://www.qsl.net
>>>>> >Please help support this email list: http://www.qsl.net/donate.html
>>>>> >Message delivered to [hidden email]
>>>>>
>>>>>
>>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:[hidden email]
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>> Message delivered to [hidden email]
>>
>>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

Don Wilhelm

Re: Fwd: Re[2]: K2 7747 VCO alignment problem

In reply to this post by Keith Hamilton

I made an error in checking K14 and K15 while on 80 meters.
It should have been conductivity between pins 2 and 3 and open between
pins 3 and 4.
The state of the other side was correct - continuity between pins 8 and
9 and open between 7 and 8.

73,
Don W3FPR
--------------------------------------------------------------------------------------------------------------------------
Keith,

C74 could explain a problem on 30, 20, and 12 meters, but you apparently
have something else awry.

If you do not find a problem with the relay coils, you should next check
the contacts of relays K13, K14 and K15.
On 20 meters, all the relays should be set - meaning you should have
conductivity from pins 3 to 4 and not between pins 2 and 3.
Check the other side of the relays - conductivity between pins 7 and 8,
and open between pins 8 and 9

Then check 80 meters, only K13 should be set - so check K14 and K15
which are reset on that band - no conductivity between pins 4 and 3 and
open between pins 2 and 3
Also check the other side, conductivity between pins 8 and 9 and open
between 7 and 8.

Then switch to 30 meters and you can check the reset state of K13 -
Continuity between pins 2 and 3 and open between pins 3 and 4
Also conductivity between pins 8 and 9 and open between pins 7 and 8.

If all that checks out, look again at the capacitor values of C71, C72,
and C73. I know some of those capacitors are tight tucked between the
relays, but bend them over a bit and use a good light and possibly a
magnifier to read the markings.

73,
Don W3FPR

On 7/13/2020 11:00 PM, Keith Hamilton wrote:

> OK Dave -
>
> I will check the relays as you suggest. In troubleshooting capacitors I
> messed up
> C74. I pulled it off the board and sent a request to Elecraft for a
> replacement.
> That may solve the problem. In the meantime I will check the coils on the
> K13 to K15
> relays and let you know what I find.
>
> I did not see Don's post. I will check it out. So I will be waiting a bit
> to fix this problem,
>
> 73 and thanks!
> Keith N8CEP
>
> On Mon, Jul 13, 2020 at 10:36 PM Dave Van Wallaghen <[hidden email]>
> wrote:
>
>> Keith,
>>
>> I saw Don respond to this and he is right that K15 would be the common
>> denominator if not for 15m. You can check to see if the coils are intact
>> if you measure the resistance between pins 1 and 10 for each. It should
>> be around 230 ohms or so. If you find one open or well away from that
>> resistance, then it would indicate a bad coil on that relay.
>>
>> You can also measure the intended path through the relays for each band
>> and make sure there are no unintended paths. If you can read the
>> schematic, it shows the path with each relay in it's reset state. You
>> would need to consult the table in Appendix B to see which relay(s) are
>> active for a respective band and you can then measure the continuity of
>> the intended path. You should also check any unintended paths which
>> could indicate a problem.
>>
>> As Don stated, this is not a fun problem to find and will take some good
>> debugging skills. So far, everything you've indicated seems to suggest
>> the PLL oscillator and VCO circuits are working properly, but the range
>> selection area is not producing the proper capacitance to allow the VCO
>> to produce the proper frequency on those bands you indicated.
>>
>> If reading the schematic is a problem, let us know and I am sure between
>> Don and myself, we can give you some step by step instructions for
>> tracing through this problem.
>>
>> 73,
>> Dave W8FGU
>>
>> ------ Original Message ------
>> From: "Keith Hamilton" <[hidden email]>
>> To: [hidden email]
>> Sent: 7/13/2020 9:34:03 PM
>> Subject: [Elecraft] Fwd: Re[2]: K2 7747 VCO alignment problem
>>
>>> ---------- Forwarded message ---------
>>> From: Keith Hamilton <[hidden email]>
>>> Date: Mon, Jul 13, 2020 at 9:19 PM
>>> Subject: Re: Re[2]: [Elecraft] K2 7747 VCO alignment problem
>>> To: Dave Van Wallaghen <[hidden email]>
>>>
>>>
>>> Dave
>>>
>>> Yes the frequency changes when turning the VFO knob when measuring with
>> CAL
>>> FCTR on TP1.
>>>
>>> I have checked the markings on C71, C72, C73, and C74 (C75 is not
>> installed
>>> yet). They are
>>> all correct and I resoldered them to be sure.
>>>
>>> I am beginning to think I might have a bad relay K13, K14 or K15. My
>>> good
>>> bands are 80,40 and
>>> 15 meters. My bad bands are 30,20,17,12 and 10 meters. Looking at the
>> relay
>>> table in appendix B
>>> I am not sure which relay could be bad. How can I test them? Should
>>> I try
>>> to replace them?
>>> 73,
>>> Keith N8CEP
>>>
>>>
>>> On Mon, Jul 13, 2020 at 4:58 PM Dave Van Wallaghen <[hidden email]>
>> wrote:
>>>
>>>> Ok Keith, just to make sure things are where we want on the bands that
>>>> seem to work, does the frequency change when turning the VFO knob when
>>>> measuring with CAL FCTR on TP1? If they do, then things are working ok.
>>>>
>>>> For the bands that are locked at 8.28v, that is the max output from the
>>>> integrator circuit (U6B). This means that there is no lock between the
>> PLL
>>>> Oscillator and the VCO circuit and the PLL chip (U4) is trying to
>> drive the
>>>> varactors to provide more capacitance to the VCO circuit. The most
>> likely
>>>> cause will be a misplaced capacitor in the VCO range selector (C71 -
>> C75)
>>>> or a problem in the VCO circuit itself. But because this may be band
>>>> dependent, I would look first in that range selection circuit. Verify
>> that
>>>> those caps are the proper values. They are easily misread and will
>> cause
>>>> the type of thing you are seeing.
>>>>
>>>> Also verify those varactor diodes are the proper type and in the right
>>>> places. Soldering issues are typically the leading cause of problems,
>> so
>>>> check that also. If all looks right to you, you may want to signal
>> trace
>>>> through that selection circuit to verify the proper relays and active
>> for
>>>> the bands not working. There is a relay table in Appendix B that shows
>> you
>>>> which relays are active for each band.
>>>>
>>>> This is a brand new build, correct?
>>>>
>>>> 73,
>>>> Dave, W8FGU
>>>>
>>>>
>>>> On 7/13/2020 4:41:07 PM, "Keith Hamilton" <[hidden email]>
>> wrote:
>>>>
>>>> Thanks for your help Dave!
>>>>
>>>> Yes. I was able to get 6 volts on R30 by turning L30. At first the
>> voltage
>>>> was too high
>>>> so I adjusted the turns on T5 by spreading the red windings further
>> apart.
>>>> Then I
>>>> was able to get to 6 volts.
>>>>
>>>> I did a CAL FCTR with the probe on TP1 and the frequency set to 4000,
>>>> The reading is 8912.22
>>>>
>>>> 73 Keith N8CEP
>>>>
>>>>
>>>> On Mon, Jul 13, 2020 at 3:59 PM Dave Van Wallaghen <[hidden email]>
>> wrote:
>>>>
>>>>> Hi Keith,
>>>>>
>>>>> Were you able to get 6v on R30 by tuning L30? Did you have to bring
>> the
>>>>> voltage down or up by moving the windings on T5?
>>>>>
>>>>> If you would, set the VFO to 4 MHz and do a CAL FCTR on TP1 and let me
>>>>> know what the reading is. I'm just looking for a couple of clues
>> before
>>>>> we proceed.
>>>>>
>>>>> 73,
>>>>> Dave, W8FGU
>>>>>
>>>>>
>>>>> On 7/13/2020 2:52:11 PM, "Keith Hamilton" <[hidden email]>
>> wrote:
>>>>>
>>>>> >I am having trouble with the K2 VCO alignment. I have moved the T5
>>>>> windings
>>>>> >and obtained 6 volts at the left end of R30. I then went on to the
>> chart
>>>>> >(table 6-1) to measure the voltages at the listed frequencies. My
>>>>> readings
>>>>> >are ok on 80 40 and 15 meters (between 1.5 to 7.5 volts) but on
>> 30,20,17
>>>>> >,12 and 10 meters the voltage is 8.29 volts and does not change.
>>>>> >
>>>>> >I have checked the solder connections of T5 and the value of C72
>> (271).
>>>>> The
>>>>> >diodes D21,D22,D23, D24, D25 and D26 are correctly installed. I also
>> went
>>>>> >over the solder connections of K13, K14 and K15.
>>>>> >
>>>>> >Now I'm stuck. Any help will be appreciated.
>>>>> >
>>>>> >Keioth Hamilton N8CEP
>>>>> >______________________________________________________________
>>>>> >Elecraft mailing list
>>>>> >Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>>>> >Help: http://mailman.qth.net/mmfaq.htm
>>>>> >Post: mailto:[hidden email]
>>>>> >
>>>>> >This list hosted by: http://www.qsl.net
>>>>> >Please help support this email list: http://www.qsl.net/donate.html
>>>>> >Message delivered to [hidden email]
>>>>>
>>>>>
>>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:[hidden email]
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>> Message delivered to [hidden email]
>>
>>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>