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[K2] VCO Not Oscillating

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Joseph Baxley

[K2] VCO Not Oscillating

Hi,

I've been trying for the last four days to figure out what is wrong with my rig. I'm at Phase 2 Test and Alignment and got to testing the frequency of the VCO. It had a reading of 00000. Also the voltage on R30 was 7.87V. This is consistent with the VCO not oscillating. The reference oscillator works fine and was within the expected ranges when I looked at it. What I was able to notice was that U4 on the RF board has two pins with voltage values that are out of spec. Pin 1 has 0.9V and pin 13 has 0V. If I read the table they should be 2.1 and 4V respectively. It also seems that the 0V on pin 13 is causing a 0V reading on pin 6 of U6. Otherwise U6 is in spec. I got out my oscilloscope and got a Vrms of 1.13V on U4 pin 1. There wasn't anything on pins 3 or 6 of U3. The voltages for Q17, Q16, and Q18 are as follows:

Q17 E: 0V
B: 7.13V
C: 0.08V

Q16 E: 0V
B: 0V
C: 7.13V

Q18 G: 0.08V
S: 6.64V
D: 0V

I have been measuring and testing voltages and components for the last four days and have run out of things to look at for the moment. If any of you can help me with what my problem is, I would be most grateful.

Sincerely,
Joseph
KI4ITG

Don Wilhelm-4

Re: [K2] VCO Not Oscillating

Joseph,

The first thing to check is T5. The direction of the windings is
critical, and the leads must be in the proper holes as shown in the
diagrams in the manual. In other words, the sense (direction) of the
green wire turns on T5 must be the same as the direction of the red wire
winding.

If that is correct, the VCO will oscillate, and things usually fall
'into line' after that once L30 is adjusted for the proper voltage at
the left end of R30.

73,
Don W3FPR

On 4/28/2014 8:22 PM, Joseph Baxley via Elecraft wrote:

> Hi,
>
> I've been trying for the last four days to figure out what is wrong with my
> rig. I'm at Phase 2 Test and Alignment and got to testing the frequency of
> the VCO. It had a reading of 00000. Also the voltage on R30 was 7.87V.
> This is consistent with the VCO not oscillating. The reference oscillator
> works fine and was within the expected ranges when I looked at it. What I
> was able to notice was that U4 on the RF board has two pins with voltage
> values that are out of spec. Pin 1 has 0.9V and pin 13 has 0V. If I read
> the table they should be 2.1 and 4V respectively. It also seems that the 0V
> on pin 13 is causing a 0V reading on pin 6 of U6. Otherwise U6 is in spec.
> I got out my oscilloscope and got a Vrms of 1.13V on U4 pin 1. There wasn't
> anything on pins 3 or 6 of U3. The voltages for Q17, Q16, and Q18 are as
> follows:
>
> Q17 E: 0V
> B: 7.13V
> C: 0.08V
>
> Q16 E: 0V
> B: 0V
> C: 7.13V
>
> Q18 G: 0.08V
> S: 6.64V
> D: 0V
>
> I have been measuring and testing voltages and components for the last four
> days and have run out of things to look at for the moment. If any of you
> can help me with what my problem is, I would be most grateful.
>
> Sincerely,
> Joseph
> KI4ITG
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-VCO-Not-Oscillating-tp7588086.html
> Sent from the Elecraft mailing list archive at Nabble.com.
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Joseph Baxley

Re: [K2] VCO Not Oscillating

Don,

Thanks for the reply. I should have mentioned that I checked the windings on T5. Pins 1 and 3 should be coming out of the top of the core, no? That's what I have. I also used the yellow core for the transformer.

Thanks,

Joseph

On Monday, April 28, 2014 8:43 PM, Don Wilhelm-4 [via Elecraft] <[hidden email]> wrote:

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vk2rq

Re: [K2] VCO Not Oscillating

Yes, leads 1 & 3 should come out the top of the core. However, you also need to make sure the windings are in the same direction, like in figure 6-16, otherwise you are applying negative instead of positive feedback, and the VCO won't oscillate.

Also, make sure leads 1 & 2 are both red, and go through the core for 16 turns. Leads 3 & 4 should both be green, and consist of 4 turns. If you get the windings backwards, then the feedback loop won't have sufficient gain, and the VCO won't oscillate.

Finally, the other problem that can occur with toroids is that the insulation on the magnet wire wasn't stripped back enough, and there is a poor joint. If this happens, the VCO won't oscillate :-)

There are other reasons why the VCO may not oscillate (eg. loading due to solder bridges, components in backwards etc.), but toroids in particular can be quite tricky and confusing, which is why Don suggests to look there first.

73, Matt VK2RQ

> On 29 Apr 2014, at 11:56 am, Joseph Baxley via Elecraft <[hidden email]> wrote:
>
> Don,
>
> Thanks for the reply. I should have mentioned that I checked the windings on T5. Pins 1 and 3 should be coming out of the top of the core, no? That's what I have. I also used the yellow core for the transformer.
>
> Thanks,
> Joseph
> On Monday, April 28, 2014 8:43 PM, Don Wilhelm-4 [via Elecraft] <[hidden email]> wrote:
>
> Joseph,
>
> The first thing to check is T5. The direction of the windings is
> critical, and the leads must be in the proper holes as shown in the
> diagrams in the manual. In other words, the sense (direction) of the
> green wire turns on T5 must be the same as the direction of the red wire
> winding.
>
> If that is correct, the VCO will oscillate, and things usually fall
> 'into line' after that once L30 is adjusted for the proper voltage at
> the left end of R30.
>
> 73,
> Don W3FPR
>
>> On 4/28/2014 8:22 PM, Joseph Baxley via Elecraft wrote:
>>
>> Hi,
>>
>> I've been trying for the last four days to figure out what is wrong with my
>> rig. I'm at Phase 2 Test and Alignment and got to testing the frequency of
>> the VCO. It had a reading of 00000. Also the voltage on R30 was 7.87V.
>> This is consistent with the VCO not oscillating. The reference oscillator
>> works fine and was within the expected ranges when I looked at it. What I
>> was able to notice was that U4 on the RF board has two pins with voltage
>> values that are out of spec. Pin 1 has 0.9V and pin 13 has 0V. If I read
>> the table they should be 2.1 and 4V respectively. It also seems that the 0V
>> on pin 13 is causing a 0V reading on pin 6 of U6. Otherwise U6 is in spec.
>> I got out my oscilloscope and got a Vrms of 1.13V on U4 pin 1. There wasn't
>> anything on pins 3 or 6 of U3. The voltages for Q17, Q16, and Q18 are as
>> follows:
>>
>> Q17 E: 0V
>> B: 7.13V
>> C: 0.08V
>>
>> Q16 E: 0V
>> B: 0V
>> C: 7.13V
>>
>> Q18 G: 0.08V
>> S: 6.64V
>> D: 0V
>>
>> I have been measuring and testing voltages and components for the last four
>> days and have run out of things to look at for the moment. If any of you
>> can help me with what my problem is, I would be most grateful.
>>
>> Sincerely,
>> Joseph
>> KI4ITG
>>
>>
>>
>> --
>> View this message in context: http://elecraft.365791.n2.nabble.com/K2-VCO-Not-Oscillating-tp7588086.html
>> Sent from the Elecraft mailing list archive at Nabble.com.
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>> 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]
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>
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>
> ________________________________
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> To unsubscribe from [K2] VCO Not Oscillating, click here.
> NAML
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-VCO-Not-Oscillating-tp7588086p7588093.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
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Don Wilhelm-4

Re: [K2] VCO Not Oscillating

In reply to this post by Joseph Baxley

Joseph,

Yes, leads 1 and 3 should be coming out of the top of the core, but the
leads must look like the illustration on page 56 of the manual, the
green wires must not cross over each other, but be wound between the red
wires.

You can check with the internal counter probe or the RF Probe to see if
the VCO is oscillating. Make certain that the leads of T5 have been
well stripped and tinned before inserting and soldering the leads.
If you look at the solder connections and see a ring around the toroid
lead, it was not well tinned and soldered. In other words, the
connection should "look like a mountain, but not a volcano".

73,
Don W3FPR

On 4/28/2014 9:56 PM, Joseph Baxley via Elecraft wrote:

> Don,
>
> Thanks for the reply. I should have mentioned that I checked the windings on T5. Pins 1 and 3 should be coming out of the top of the core, no? That's what I have. I also used the yellow core for the transformer.
>
> Thanks,
> Joseph
> On Monday, April 28, 2014 8:43 PM, Don Wilhelm-4 [via Elecraft] <[hidden email]> wrote:
>
> Joseph,
>
> The first thing to check is T5. The direction of the windings is
> critical, and the leads must be in the proper holes as shown in the
> diagrams in the manual. In other words, the sense (direction) of the
> green wire turns on T5 must be the same as the direction of the red wire
> winding.
>
> If that is correct, the VCO will oscillate, and things usually fall
> 'into line' after that once L30 is adjusted for the proper voltage at
> the left end of R30.
>
>

Joseph Baxley

Re: [K2] VCO Not Oscillating

In reply to this post by Joseph Baxley

Don, Matt,

I looked at the transformer and have double checked him. I saw that there was electrical continuity between leads 1 & 2 and 3 & 4 (i.e. zero Ohm resistance between said leads). Also, 3 & 4 are the green leads. I checked that the green wires weren't crossing and that they were spaced each turn between the red wires. I did notice that they weren't exactly centered, with more red turns before lead three than after lead four. I pulled the transformer out and rewound the green wires to center them and see if it helped any. No dice. Also I checked the number of turns, 16 red and 4 green. I'm intimately familiar with not having properly stripped the wires. That was a problem building my K1!

I'm fairly certain then that the transformer is not the problem. I've been checking things like the diodes that run through the VCO to make sure that I have not put in one backwards. I've also been looking for cold joints or solder bridges. Haven't found one yet.

Thanks,
Joseph

Don Wilhelm-4

Re: [K2] VCO Not Oscillating

Joseph,

See if the VFO is oscillating. Check the internal counter probe by
plugging it into TP2 and use menu CAL FCTR - you should see a frequency
near 4913 kHz (the BFO frequency). If that is good, the counter probe
should be working. Then plug the probe into TP1. The frequency should
be near the K2 dial frequency plus 4913 kHz. If you see that frequency,
all is OK with the VFO.

If you instead see all zeros, the VFO is not oscillating, and you will
have to figure out why.
You have already checked the winding of T5, so there may be something
else. Check the orientation of D13 and D8 as starters. Then eliminate
the VFO ALC from the picture by placing a short from the drsin og Q17 to
ground (a convenient place to do that is to put a temporary solder
bridge across the leads of C50). Do you get a VFO frequency reading
with that in place? If so check the soldering of the VFO ALC
components. Look on the schematic and find on sheet 1 for the RF Board
all the components in the area labeled VFO ALC and check the soldering
of all those components - remove the solder bridge from C50 and see if
it still oscillates. If it does, you should be on your way to success.

73,
Don W3FPR

On 4/29/2014 9:13 PM, Joseph Baxley via Elecraft wrote:

> Don, Matt,
>
> I looked at the transformer and have double checked him. I saw that there
> was electrical continuity between leads 1 & 2 and 3 & 4 (i.e. zero Ohm
> resistance between said leads). Also, 3 & 4 are the green leads. I checked
> that the green wires weren't crossing and that they were spaced each turn
> between the red wires. I did notice that they weren't exactly centered,
> with more red turns before lead three than after lead four. I pulled the
> transformer out and rewound the green wires to center them and see if it
> helped any. No dice. Also I checked the number of turns, 16 red and 4
> green. I'm intimately familiar with not having properly stripped the wires.
> That was a problem building my K1!
>
> I'm fairly certain then that the transformer is not the problem. I've been
> checking things like the diodes that run through the VCO to make sure that I
> have not put in one backwards. I've also been looking for cold joints or
> solder bridges. Haven't found one yet.
>
> Thanks,
> Joseph
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-VCO-Not-Oscillating-tp7588086p7588156.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> 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]
>

Joseph Baxley

Re: [K2] VCO Not Oscillating

Don,

Thanks again. I had one question from your last email. Did you mean C60? I couldn't find C50 in the VFO circuit. I shorted C60 which put the drain to ground. Still no help. The BFO is working though, so that's good news. I also checked D13 and D8. They match the outline on the board, so they should be good. I will try again tomorrow when I've had some rest. Sometimes I've found fresh eyes help me see things I missed the night before.

Joseph

On Tuesday, April 29, 2014 9:15 PM, Don Wilhelm-4 [via Elecraft] <[hidden email]> wrote:

If you reply to this email, your message will be added to the discussion below:

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NAML

W2RMS

Calibrating KTCXO3 with the XG3

Hello again, everyone!
I just installed the K3EXREF board in my K3 and i also have the KTCXO3 unit in there from before.
The idea was to use the XG3 as the external 10 MHz reference for calibration.
I wasn't thrilled with the accuracy of the zero-beat method that i was using (or rather i wasn't thrilled with MY accuracy).
I think i did the procedure correctly: went to REF CAL menu, enabled the K3EXREF, hooked up the BNC cable, the asterisk started flashing, the frequency changed (clearly the zero-beat i did before wasn't correct).
My only question is about the output level of the XG3: i used the zero dBm. But the calibration procedure mentioned that the reference signal should be between +4 dBm and something else (higher).
XG3 doesn't seem to go that high though. Is that ok? Using zero dBm for this?

Thanks in advance!

Slava B
W2RMS
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Don Wilhelm-4

Re: [K2] VCO Not Oscillating

In reply to this post by Joseph Baxley

Joseph,

Blame it on poor lighting at the computer (and my eyes) - yes, C60 is
the appropriate capacitor.
So the VFO ALC is not the problem - you will have to discover why the
VFO is not oscillating. It could be a problem with Q18 or anything in
its circuit. Do check Q18 for the correct FET type (J310) and the
orientation of D13 and D8 - refer to the parts placement diagram in the
back of the manual for the diode orientation.

73,
Don W3FPR

On 4/29/2014 10:51 PM, Joseph Baxley via Elecraft wrote:

> Don,
>
> Thanks again. I had one question from your last email. Did you mean C60? I couldn't find C50 in the VFO circuit. I shorted C60 which put the drain to ground. Still no help. The BFO is working though, so that's good news. I also checked D13 and D8. They match the outline on the board, so they should be good. I will try again tomorrow when I've had some rest. Sometimes I've found fresh eyes help me see things I missed the night before.
>
> Joseph
>
>
>
>
> On Tuesday, April 29, 2014 9:15 PM, Don Wilhelm-4 [via Elecraft] <[hidden email]> wrote:
>
> Joseph,
>
> See if the VFO is oscillating. Check the internal counter probe by
> plugging it into TP2 and use menu CAL FCTR - you should see a frequency
> near 4913 kHz (the BFO frequency). If that is good, the counter probe
> should be working. Then plug the probe into TP1. The frequency should
> be near the K2 dial frequency plus 4913 kHz. If you see that frequency,
> all is OK with the VFO.
>
> If you instead see all zeros, the VFO is not oscillating, and you will
> have to figure out why.
> You have already checked the winding of T5, so there may be something
> else. Check the orientation of D13 and D8 as starters. Then eliminate
> the VFO ALC from the picture by placing a short from the drsin og Q17 to
> ground (a convenient place to do that is to put a temporary solder
> bridge across the leads of C50). Do you get a VFO frequency reading
> with that in place? If so check the soldering of the VFO ALC
> components. Look on the schematic and find on sheet 1 for the RF Board
> all the components in the area labeled VFO ALC and check the soldering
> of all those components - remove the solder bridge from C50 and see if
> it still oscillates. If it does, you should be on your way to success.
>
> 73,
> Don W3FPR
>
> On 4/29/2014 9:13 PM, Joseph Baxley via Elecraft wrote:
>
>> Don, Matt,
>>
>> I looked at the transformer and have double checked him. I saw that there
>> was electrical continuity between leads 1 & 2 and 3 & 4 (i.e. zero Ohm
>> resistance between said leads). Also, 3 & 4 are the green leads. I checked
>> that the green wires weren't crossing and that they were spaced each turn
>> between the red wires. I did notice that they weren't exactly centered,
>> with more red turns before lead three than after lead four. I pulled the
>> transformer out and rewound the green wires to center them and see if it
>> helped any. No dice. Also I checked the number of turns, 16 red and 4
>> green. I'm intimately familiar with not having properly stripped the wires.
>> That was a problem building my K1!
>>
>> I'm fairly certain then that the transformer is not the problem. I've been
>> checking things like the diodes that run through the VCO to make sure that I
>> have not put in one backwards. I've also been looking for cold joints or
>> solder bridges. Haven't found one yet.
>>
>> Thanks,
>> Joseph
>>
>>
>>
>> --
>> View this message in context: http://elecraft.365791.n2.nabble.com/K2-VCO-Not-Oscillating-tp7588086p7588156.html
>> Sent from the Elecraft mailing list archive at Nabble.com.
>> ______________________________________________________________
>> 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]
>>
> ______________________________________________________________
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>
> ________________________________
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> To unsubscribe from [K2] VCO Not Oscillating, click here.
> NAML
>
>
>
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vk2rq

Re: [K2] VCO Not Oscillating

In reply to this post by Joseph Baxley

Hi Joseph,

Just taking a closer look at the voltages you reported on Q16, Q17 & Q18:
Q17 should be a 2N7000 MOSFET, but the measurements you provided talk about Base, Emitter and Collector (rather than Gate, Source and Drain).

Also, the Drain of Q17 has a DC connection to the Source of Q18. You report the Source of Q18 as being 6.64V, but if there is no oscillation then this isn't consistent with the voltages you reported on Q17.

Can you maybe check you have used the right transistors, verify the orientation/pin outs, and recheck that the voltages you are reporting against each transistor and each transistor terminal are correct? Somehow something doesn't quite seem to add up with what you reported below :-)

Another obvious thing is to verify is the orientation of ICs U3 and U4.

73,
Matt VK2RQ

> On 29 Apr 2014, at 10:22 am, Joseph Baxley via Elecraft <[hidden email]> wrote:
>
> Hi,
>
> I've been trying for the last four days to figure out what is wrong with my
> rig. I'm at Phase 2 Test and Alignment and got to testing the frequency of
> the VCO. It had a reading of 00000. Also the voltage on R30 was 7.87V.
> This is consistent with the VCO not oscillating. The reference oscillator
> works fine and was within the expected ranges when I looked at it. What I
> was able to notice was that U4 on the RF board has two pins with voltage
> values that are out of spec. Pin 1 has 0.9V and pin 13 has 0V. If I read
> the table they should be 2.1 and 4V respectively. It also seems that the 0V
> on pin 13 is causing a 0V reading on pin 6 of U6. Otherwise U6 is in spec.
> I got out my oscilloscope and got a Vrms of 1.13V on U4 pin 1. There wasn't
> anything on pins 3 or 6 of U3. The voltages for Q17, Q16, and Q18 are as
> follows:
>
> Q17 E: 0V
> B: 7.13V
> C: 0.08V
>
> Q16 E: 0V
> B: 0V
> C: 7.13V
>
> Q18 G: 0.08V
> S: 6.64V
> D: 0V
>
> I have been measuring and testing voltages and components for the last four
> days and have run out of things to look at for the moment. If any of you
> can help me with what my problem is, I would be most grateful.
>
> Sincerely,
> Joseph
> KI4ITG
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-VCO-Not-Oscillating-tp7588086.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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Don Wilhelm-4

Re: Calibrating KTCXO3 with the XG3

In reply to this post by W2RMS

Slava,

Most external reference sources have an output of +10 dBm or somewhere
around that level.
It is not a matter of simply calibrating, the external reference is
intended to be connected continuously.
Yes, there is a data table created that can be used when the reference
is not present.

I really can't answer about the level of the XG3, but I am certain the
frequency accuracy it is not as tight as a real external reference -
rubidium standard or GPS disiplined oscillator. The spec for the XG3 is
+/- 50 ppm while an external reference is typically stated in parts per
billion.

73,
Don W3FPR

On 4/29/2014 11:18 PM, Slava Baytalskiy wrote:
> Hello again, everyone!
> I just installed the K3EXREF board in my K3 and i also have the KTCXO3 unit in there from before.
> The idea was to use the XG3 as the external 10 MHz reference for calibration.
> I wasn't thrilled with the accuracy of the zero-beat method that i was using (or rather i wasn't thrilled with MY accuracy).
> I think i did the procedure correctly: went to REF CAL menu, enabled the K3EXREF, hooked up the BNC cable, the asterisk started flashing, the frequency changed (clearly the zero-beat i did before wasn't correct).
> My only question is about the output level of the XG3: i used the zero dBm. But the calibration procedure mentioned that the reference signal should be between +4 dBm and something else (higher).
> XG3 doesn't seem to go that high though. Is that ok? Using zero dBm for this?
>
>

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Matt Zilmer-2

Re: Calibrating KTCXO3 with the XG3

Typically, the Trimble Thunderbolt GPSDO 10 MHZ reference exceeds
+/-100 PPT. Not sure of the statistics, but that's the high end of
the range Lady Heather reports. This GPSDO outputs a slightly
distorted sine wave at around 8 dBm, which is within the K3's rated
input range. I just leave mine connected full-time.

73,
matt W6NIA

On Wed, 30 Apr 2014 09:25:02 -0400, you wrote:

>Slava,
>
>Most external reference sources have an output of +10 dBm or somewhere
>around that level.
>It is not a matter of simply calibrating, the external reference is
>intended to be connected continuously.
>Yes, there is a data table created that can be used when the reference
>is not present.
>
>I really can't answer about the level of the XG3, but I am certain the
>frequency accuracy it is not as tight as a real external reference -
>rubidium standard or GPS disiplined oscillator. The spec for the XG3 is
>+/- 50 ppm while an external reference is typically stated in parts per
>billion.
>
>73,
>Don W3FPR
>
>On 4/29/2014 11:18 PM, Slava Baytalskiy wrote:
>> Hello again, everyone!
>> I just installed the K3EXREF board in my K3 and i also have the KTCXO3 unit in there from before.
>> The idea was to use the XG3 as the external 10 MHz reference for calibration.
>> I wasn't thrilled with the accuracy of the zero-beat method that i was using (or rather i wasn't thrilled with MY accuracy).
>> I think i did the procedure correctly: went to REF CAL menu, enabled the K3EXREF, hooked up the BNC cable, the asterisk started flashing, the frequency changed (clearly the zero-beat i did before wasn't correct).
>> My only question is about the output level of the XG3: i used the zero dBm. But the calibration procedure mentioned that the reference signal should be between +4 dBm and something else (higher).
>> XG3 doesn't seem to go that high though. Is that ok? Using zero dBm for this?
>>
>>
>
>______________________________________________________________
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Matt Zilmer, W6NIA
www.elecraft.com
831-763-4211 x129

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Joseph Baxley

Re: [K2] VCO Not Oscillating

In reply to this post by vk2rq

Matt,

My reason for asserting that the VCO is not oscillating is two-fold. One, there is no frequency at TP1 when I touch it with the probe, but there is when I touch TP2 and TP3. Both of these test points show a correct oscillation of 4.9MHz and 12.09MHz respectively. Second, when I applied my voltmeter to R30 and tried turn the slug for L30 there was no change in the voltage at R30. I will recheck both of these assertions.

I looked over my notes for Q17 and realized that I had them mis-labeled when I wrote the first email in this chain. Looking at the notes I have with me the labeling is S: 0V, G: 7.14V, and D: 0.08V. I will of course check these again when I go back to work on the radio as well as the part types, though I'm fairly certain they are correct. I'm taking the night off though. Also, I did check U3 and U4 over several times and recall them being in the correct orientation. Will look again here as well.

The action plan for tomorrow is to double check all components in the VCO for correct value and orientation and then to re-heat the solder joints on them. Hopefully it will be something simple and stupid like a misplaced part or a cold joint.

Thanks,
Joseph

vk2rq

Re: [K2] VCO Not Oscillating

Ok, that makes more sense now, although we now have the Drain of Q17
at 0.08V connected to the Source of Q18 at 6.64V via the primary
(green) winding of T5. I would hazzard a guess that there is also a
clerical error with the Q18 voltages, and that the Source is at 0.08V,
same as the Drain of Q17, the Gate of Q18 is at 0V, and the Source of
Q18 is at 6.67V. The alternative would be that the T5 primary winding
is open circuit, but then the other voltages wouldn't make sense.

There is minimal ALC voltage on Q17 Drain, so this supports your
conclusion that the VCO is not oscillating, although it could also be
that either Q16 or the U3 buffer is not working. An RF probe to pin 3
of the U3 buffer will tell you if there is any signal there.

You might check that all the variactor diodes are in the right way
(D21-D26) and the right type (D21 & D22 are 1SV149, D23 & D24 are
MV209) and that L30 is ok (no red line, large adjustment slot). You
could perhaps try changing bands to toggle the K13/K14/K15 relays to
isolate the associated components and see if the VCO starts
oscillating.

As you say, if any joints look suspect, reflowing them is not a bad idea.

Good luck, let us know how you go.

73, Matt VK2RQ

The most exciting phrase to hear in science, the one that heralds new
discoveries, is not 'Eureka!' but 'That's funny...' -- Isaac Asimov

On Thu, May 1, 2014 at 11:59 AM, Joseph Baxley via Elecraft
<[hidden email]> wrote:

> Matt,
>
> My reason for asserting that the VCO is not oscillating is two-fold. One,
> there is no frequency at TP1 when I touch it with the probe, but there is
> when I touch TP2 and TP3. Both of these test points show a correct
> oscillation of 4.9MHz and 12.09MHz respectively. Second, when I applied my
> voltmeter to R30 and tried turn the slug for L30 there was no change in the
> voltage at R30. I will recheck both of these assertions.
>
> I looked over my notes for Q17 and realized that I had them mis-labeled when
> I wrote the first email in this chain. Looking at the notes I have with me
> the labeling is S: 0V, G: 7.14V, and D: 0.08V. I will of course check these
> again when I go back to work on the radio as well as the part types, though
> I'm fairly certain they are correct. I'm taking the night off though.
> Also, I did check U3 and U4 over several times and recall them being in the
> correct orientation. Will look again here as well.
>
> The action plan for tomorrow is to double check all components in the VCO
> for correct value and orientation and then to re-heat the solder joints on
> them. Hopefully it will be something simple and stupid like a misplaced
> part or a cold joint.
>
> Thanks,
> Joseph
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-VCO-Not-Oscillating-tp7588086p7588251.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> 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-4

Re: [K2] VCO Not Oscillating

Joseph,

I don't know if you are mislabeling the leads of Q18 or not, but those
voltages and the leads do not make sense.
The Drain of Q18 is connected to the 8B voltage rail through a 33 ohm
resistor and should have almost 8 volts on it.
The Gate is biased by the rectification of the RF voltage by D13, and
when oscillating should have a negative voltage (the fact that you show
no negative voltage says Q18 is not oscillating).
The Q18 Source would normally have 2 to 3 volts on it, but since Q18 is
not oscillating, there is no VFO RF being applied to D11, and that means
Q18 will not conduct - that places the gate of Q17 at a high voltage and
saturates the Drain to Source of Q18 which will produce 0 volts at the
Q18 Source.

Refer to the Schematic Key page in the back of the manual for the proper
lead callouts for the J310 transistor.

In other words, Q18 is simply not oscillating for you. Look at the
schematic for the RF board Sheet 1 in the upper right quadrant. Check
each component shown there for proper values and good soldering. Make
certain Q18, Q17, and Q16 are oriented correctly and diodes D11, D8 and
D13 are oriented correctly (look at the Parts Placement Diagram in the
back of the manual).

Be certain varactors D21 thru D26 are oriented correctly.
If it still does not oscillate, rewind T5 being especially careful to
make it look exactly like the diagram in the manual and make certain the
leads are well stripped and tinned before installing it onto the board.
If all that is correct, it will oscillate at some frequency. If the
frequency is not correct, that is a different matter, but if everything
above is correct, it will oscillate.

You could try another J310 at Q18. There is one that should not be
mounted yet in your build which would eventually be used at Q24. If
that fixes the VFO, ask [hidden email] for a replacement J310.

73,
Don W3FPR

On 4/30/2014 11:44 PM, Matt Maguire wrote:

> Ok, that makes more sense now, although we now have the Drain of Q17
> at 0.08V connected to the Source of Q18 at 6.64V via the primary
> (green) winding of T5. I would hazzard a guess that there is also a
> clerical error with the Q18 voltages, and that the Source is at 0.08V,
> same as the Drain of Q17, the Gate of Q18 is at 0V, and the Source of
> Q18 is at 6.67V. The alternative would be that the T5 primary winding
> is open circuit, but then the other voltages wouldn't make sense.
>
> There is minimal ALC voltage on Q17 Drain, so this supports your
> conclusion that the VCO is not oscillating, although it could also be
> that either Q16 or the U3 buffer is not working. An RF probe to pin 3
> of the U3 buffer will tell you if there is any signal there.
>
> You might check that all the variactor diodes are in the right way
> (D21-D26) and the right type (D21 & D22 are 1SV149, D23 & D24 are
> MV209) and that L30 is ok (no red line, large adjustment slot). You
> could perhaps try changing bands to toggle the K13/K14/K15 relays to
> isolate the associated components and see if the VCO starts
> oscillating.
>
> As you say, if any joints look suspect, reflowing them is not a bad idea.
>
> Good luck, let us know how you go.
>
> 73, Matt VK2RQ
>
> The most exciting phrase to hear in science, the one that heralds new
> discoveries, is not 'Eureka!' but 'That's funny...' -- Isaac Asimov
>
> On Thu, May 1, 2014 at 11:59 AM, Joseph Baxley via Elecraft
> <[hidden email]> wrote:
>> Matt,
>>
>> My reason for asserting that the VCO is not oscillating is two-fold. One,
>> there is no frequency at TP1 when I touch it with the probe, but there is
>> when I touch TP2 and TP3. Both of these test points show a correct
>> oscillation of 4.9MHz and 12.09MHz respectively. Second, when I applied my
>> voltmeter to R30 and tried turn the slug for L30 there was no change in the
>> voltage at R30. I will recheck both of these assertions.
>>
>> I looked over my notes for Q17 and realized that I had them mis-labeled when
>> I wrote the first email in this chain. Looking at the notes I have with me
>> the labeling is S: 0V, G: 7.14V, and D: 0.08V. I will of course check these
>> again when I go back to work on the radio as well as the part types, though
>> I'm fairly certain they are correct. I'm taking the night off though.
>> Also, I did check U3 and U4 over several times and recall them being in the
>> correct orientation. Will look again here as well.
>>
>> The action plan for tomorrow is to double check all components in the VCO
>> for correct value and orientation and then to re-heat the solder joints on
>> them. Hopefully it will be something simple and stupid like a misplaced
>> part or a cold joint.
>>
>> Thanks,
>> Joseph
>>

Joseph Baxley

Re: [K2] VCO Not Oscillating

Don, Matt,

It is possible that I've mislabeled things, though I was trying to follow the diagram they have before the schematics that describes each part. Really I've not got a lot of experience with electronics beyond a couple of classes in college. It's not something they stressed in the physics department unfortunately. That's part of why I'm building the rig. It's an educational experience :)

I did wind up trying another J310 that I lifted out of the KIO2 option board I purchased with no luck. I have also ran over all the components in the synthesizer looking for correct value and orientation. I did not find anything out of the ordinary. At this point I am thinking of asking if the fellows at Elecraft in California will look at it. If I have to pull too many parts I'd be afraid of damaging the RF board. Once I get past this part of assembly, I should be fine to finish the rig.

Thanks,
Joseph

Joseph Baxley

Re: [K2] VCO Not Oscillating

P.S. I really would like to thank you all for your help.

Joseph Baxley

Re: [K2] VCO Not Oscillating

Hey,

I wanted to let you guys know that the root cause has been found. I asked Don to look at the radio and the root cause was that I had misplaced a 1pF cap at C68 which was labeled 1D. C68 was supposed to be 10pF. It was a stupid construction mistake after all. Perhaps this can serve as a nice data point for anyone else building the K2 that has a similar problem. I will be getting the radio back soon and hope to finish the kit without incident.

Thanks,
Joseph KI4ITG

Johnny Siu

[K2] VCO Not Oscillating

We did make similar mistakes throught out our hobby. Wrong parts, wrong components at wrong places are always the problems.

Even I built the 10th K2, I still made mistakes.

73

Johnny VR2XMC

________________________________
寄件人︰ Joseph Baxley via Elecraft <[hidden email]>
收件人︰ [hidden email]
傳送日期︰ 2014年05月12日 (週一) 11:59 AM
主題︰ Re: [Elecraft] [K2] VCO Not Oscillating

Hey,

I wanted to let you guys know that the root cause has been found. I asked
Don to look at the radio and the root cause was that I had misplaced a 1pF
cap at C68 which was labeled 1D. C68 was supposed to be 10pF. It was a
stupid construction mistake after all. Perhaps this can serve as a nice
data point for anyone else building the K2 that has a similar problem. I
will be getting the radio back soon and hope to finish the kit without
incident.

Thanks,
Joseph KI4ITG

--
View this message in context: http://elecraft.365791.n2.nabble.com/K2-VCO-Not-Oscillating-tp7588086p7588948.html
Sent from the Elecraft mailing list archive at Nabble.com.
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