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K2 BFO not oscillating

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Conway Yee

K2 BFO not oscillating

TP2 reads 0 MHz.

Checking the components involving the BFO, No obvious missing components.
No obvious cold joints.

I checked the to pads adjacent to L33 which I believe to be the pads to
the BFO crystal filters (two more are hidden under L33). With power on,
the voltages are different making me suspect that I did not short the
crystals.

The manual tells me that the BFO isn't working or the frequency probe is
not hooked up (which it is). It also tells me to go to the
troubleshooting section. The table in the section doesn't seem to
illuminate anything. The signal tracing part only seems to tell me to
check the voltages (which are lower than the 0.020 volts).

What do I do?

tnx.
Conway Yee, N2JWQ

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Don Wilhelm-4

Re: K2 BFO not oscillating

Conway,

Does your counter probe report a frequency reading when plugged into
TP1? If so, the probe is working, if not, then your problem is with
either the probe itself or the Q9 and Q10 circuits on the Control Board.

If (and only if) the probe works in TP1, then do the following -
otherwise skip the steps below.
Turn your manual to Appendix E page 11 and do the 4 test steps indicated
at the top of the 1st column. Then compare the DC voltages during CAL
FCTR at the leads of Q24 and U11. If that does not reveal the problem
for you, tell us what those measurements are an we may be able to help.

73,
Don W3FPR

Conway Yee wrote:

> TP2 reads 0 MHz.
>
> Checking the components involving the BFO, No obvious missing components.
> No obvious cold joints.
>
> I checked the to pads adjacent to L33 which I believe to be the pads to
> the BFO crystal filters (two more are hidden under L33). With power on,
> the voltages are different making me suspect that I did not short the
> crystals.
>
> The manual tells me that the BFO isn't working or the frequency probe is
> not hooked up (which it is). It also tells me to go to the
> troubleshooting section. The table in the section doesn't seem to
> illuminate anything. The signal tracing part only seems to tell me to
> check the voltages (which are lower than the 0.020 volts).
>
> What do I do?
>
> tnx.
> Conway Yee, N2JWQ
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
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>
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>

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Conway Yee

Re: K2 BFO not oscillating

> Does your counter probe report a frequency reading when plugged into
> TP1? If so, the probe is working, if not, then your problem is with
> either the probe itself or the Q9 and Q10 circuits on the Control Board.

The frequency probe is fine.

TP3 shows 12099.11
when I switch to TP2, I read zero.

> Turn your manual to Appendix E page 11 and do the 4 test steps indicated
> at the top of the 1st column. Then compare the DC voltages during CAL
> FCTR at the leads of Q24 and U11. If that does not reveal the problem
> for you, tell us what those measurements are an we may be able to help.

>From Appendix E, the BFO fails to oscillate.
BFO Output : Vrms = 0.001
BFO buffer output : Vrms = 0.008

[measurments done with Fluke 77, AC voltage]

U11 DC voltages appear nominal
pin 1 : 1.403 manual 1.4
2 : 1.403 1.4
3 : 0 0
4 : 4.75 5.0
5 : 4.76 5.0
6 : 5.86 6.1
7 : 5.44 5.6
8 : 5.92 6.1

Q24 DC voltages are abnormal
S : 0 manual 0.0
G : 0 1.2
D : 0 1.3

Looking at the circuit diagram, nothing is soldered to the other side of
R98, V_{alc}. Could this be the problem?

I am unable to find where in the circuit diagram V_{alc} is hiding.

On the circuit board, it appears that jumpers are supposed to be there. I
am also unable to find in the construction instructions I was supposed
to (or not) place what appears to be jumpers in the area.

tnx.
Conway Yee, N2JWQ
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Don Wilhelm-4

Re: K2 BFO not oscillating

Conway,

The DC Voltages are OK - even for Q24. Recall that I asked you to
measure while in CAL FCTR. That places a voltage on the VALC signal
line. It normally is used for power control and is developed on the
Control Board at Q8.

So the problem is that the BFO is not oscillating. First steps are to
check soldering of the BFO components X3, X4, C174, C173, D38 and D39.
Examine L33 carefully to be certain the very fine wires are soldered to
the leads of the 1/8 watt resistor.
Measure the resistance between the solder pads that L33 and its mounting
resistor are soldered to - if the resistance is in the megohm range,
then L33 either has an unsoldered lead or has a broken wire.
Check the orientation of D38 and D37.

The other components in the BFO circuit help control the frequency, but
your problem is that it is not oscillating.

Jumpers are not the problem, but you should have installed W1 through W6
during the Assembly Part II

73,
Don W3FPR

Conway Yee wrote:

>> Does your counter probe report a frequency reading when plugged into
>> TP1? If so, the probe is working, if not, then your problem is with
>> either the probe itself or the Q9 and Q10 circuits on the Control Board.
>>
>
> The frequency probe is fine.
>
> TP3 shows 12099.11
> when I switch to TP2, I read zero.
>
>
>> Turn your manual to Appendix E page 11 and do the 4 test steps indicated
>> at the top of the 1st column. Then compare the DC voltages during CAL
>> FCTR at the leads of Q24 and U11. If that does not reveal the problem
>> for you, tell us what those measurements are an we may be able to help.
>>
>
> >From Appendix E, the BFO fails to oscillate.
> BFO Output : Vrms = 0.001
> BFO buffer output : Vrms = 0.008
>
> [measurments done with Fluke 77, AC voltage]
>
> U11 DC voltages appear nominal
> pin 1 : 1.403 manual 1.4
> 2 : 1.403 1.4
> 3 : 0 0
> 4 : 4.75 5.0
> 5 : 4.76 5.0
> 6 : 5.86 6.1
> 7 : 5.44 5.6
> 8 : 5.92 6.1
>
> Q24 DC voltages are abnormal
> S : 0 manual 0.0
> G : 0 1.2
> D : 0 1.3
>
> Looking at the circuit diagram, nothing is soldered to the other side of
> R98, V_{alc}. Could this be the problem?
>
> I am unable to find where in the circuit diagram V_{alc} is hiding.
>
> On the circuit board, it appears that jumpers are supposed to be there. I
> am also unable to find in the construction instructions I was supposed
> to (or not) place what appears to be jumpers in the area.
>
> tnx.
> Conway Yee, N2JWQ
>
>

Conway Yee

Re: K2 BFO not oscillating

On Wed, 3 Feb 2010, Don Wilhelm wrote:
> So the problem is that the BFO is not oscillating.

Searching some more, I am no longer certain that this is the case, I have
been using a Fluke 77 for AC voltage measurements. Checking the spec
sheet, it appears thaat AC voltages are measured from 100mV to 750V with a
frequency range from 45Hz to 1KHz. Certainly the BFO voltages are too low
and the frequency too high to register.

Testing this theory, I place my Fluke 77 to TP3 which is KNOWN to have
12099Hz, I read 0V. This MAY explain my zero measurements on TP2 and pin
6 of U11.

Trying the frequency probe on pin 6, I see 4913.11Hz!!!! This is also seen
on pin 7 (as expected). I also see the same on both sides of D37
(although slightly higher frequency 4913.38Hz. Nothing is seen on TP2.
and possibly on C168 (unstable number much smaller than 4913, mostly in
the 2000 range). In summary, assuming that the signal is from the
crystal, I see it up to the gate of J310 but not on the source.

Does this mean that I have managed to fry Q24?

I note that V_{alc} is zero. Could I have missed something that is
supposed to be hooked up to the other side of R98? I still can't find a
jumper in the instructions that is supposed to be soldered to the tracing
extending from the other side of R98 toward the control board.

Also, what test equipment am I supposed to purchase that is able to
measure voltages in the MHz range? I can break out my oscilloscope but
this seems overkill for the job. Is there a handheld multimeter that can
handle HF frequency measurements?

tnx.
Conway Yee, N2JWQ
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Don Wilhelm-4

Re: K2 BFO not oscillating

Conway,

If you have an oscilloscope, dragging it out is *not* overkill - it will
show you the peak to peak RF voltages as well as the waveform.
Lacking the 'scope, you can build up the RF Probe - the parts are
supplied with the K2 kit and the circuit board is part of the 'switch
spacing tool'. That RF Probe will indicate the RMS value of the RF
Voltage on your DMM.
I can't say what the response of your Fluke 77 may be on AC, but I made
a check with my Fluke 179 and at the 4915 MHz frequency, it does provide
a response comparable you your measurements.

Are you attempting to measure the Q24 response while either in transmit
or in the menu CAL FCTR state? If not, then your results are as
expected - Q24 does not pass the BFO signal on receive due to the
absence of voltage on the VALC signal line.

If you *are* in either CAL FCTR or transmit state when measuring at TP2,
then yes, Q24 may be the problem.

73,
Don W3FPR

Conway Yee wrote:

> On Wed, 3 Feb 2010, Don Wilhelm wrote:
>
>> So the problem is that the BFO is not oscillating.
>>
>
> Searching some more, I am no longer certain that this is the case, I have
> been using a Fluke 77 for AC voltage measurements. Checking the spec
> sheet, it appears thaat AC voltages are measured from 100mV to 750V with a
> frequency range from 45Hz to 1KHz. Certainly the BFO voltages are too low
> and the frequency too high to register.
>
> Testing this theory, I place my Fluke 77 to TP3 which is KNOWN to have
> 12099Hz, I read 0V. This MAY explain my zero measurements on TP2 and pin
> 6 of U11.
>
> Trying the frequency probe on pin 6, I see 4913.11Hz!!!! This is also seen
> on pin 7 (as expected). I also see the same on both sides of D37
> (although slightly higher frequency 4913.38Hz. Nothing is seen on TP2.
> and possibly on C168 (unstable number much smaller than 4913, mostly in
> the 2000 range). In summary, assuming that the signal is from the
> crystal, I see it up to the gate of J310 but not on the source.
>
> Does this mean that I have managed to fry Q24?
>
> I note that V_{alc} is zero. Could I have missed something that is
> supposed to be hooked up to the other side of R98? I still can't find a
> jumper in the instructions that is supposed to be soldered to the tracing
> extending from the other side of R98 toward the control board.
>
> Also, what test equipment am I supposed to purchase that is able to
> measure voltages in the MHz range? I can break out my oscilloscope but
> this seems overkill for the job. Is there a handheld multimeter that can
> handle HF frequency measurements?
>
> tnx.
> Conway Yee, N2JWQ
> ______________________________________________________________
> 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
> ------------------------------------------------------------------------
>
>
> No virus found in this incoming message.
> Checked by AVG - www.avg.com
> Version: 9.0.733 / Virus Database: 271.1.1/2667 - Release Date: 02/04/10 02:35:00
>
>

Conway Yee

Re: K2 BFO not oscillating

> expected - Q24 does not pass the BFO signal on receive due to the
> absence of voltage on the VALC signal line.

Thats it! Your clue led me to trace V_{alc} back to the control board.
I NEVER had a non-zero measurement on V_{alc} even though I was in CAL
FCTR.

It turns out that I forgot to solder pin 1 on U10 on the control board.
Oops. Once soldered, TP2 is happy.

tnx.
Conway Yee

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Don Wilhelm-4

Re: K2 BFO not oscillating

Conway,

It is great news that you have found the source of the problem.
Onward to the rest of the K2 build, and I wish you no more unsoldered pins.

73,
Don W3FPR

Conway Yee wrote:

>> expected - Q24 does not pass the BFO signal on receive due to the
>> absence of voltage on the VALC signal line.
>>
>
> Thats it! Your clue led me to trace V_{alc} back to the control board.
> I NEVER had a non-zero measurement on V_{alc} even though I was in CAL
> FCTR.
>
> It turns out that I forgot to solder pin 1 on U10 on the control board.
> Oops. Once soldered, TP2 is happy.
>
> tnx.
> Conway Yee
>
> ______________________________________________________________
> 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
> ------------------------------------------------------------------------
>
>
> No virus found in this incoming message.
> Checked by AVG - www.avg.com
> Version: 9.0.733 / Virus Database: 271.1.1/2667 - Release Date: 02/04/10 02:35:00
>
>