K2 BFO problem

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K2 BFO problem

Ken Mohler
Hi Gang -

 

I'm building my 2nd K2 and am at the point of Alignment and Test, Part II.
All of the tests and alignment steps through the VCO alignment have been
completed successfully.  Everything has been right in the center of the
expected parameters.  Then I got to the BFO test.  I'm getting a reading of
0000.00.  Here's what I know so far:  D37 and D38 are the correct types and
oriented properly.  I have measured the resistance across the resistor
holding L33 down (or up?) and get a reading of 1.5 ohms, indicating to me
that L33 is intact and effectively soldered to the resistor leads.  I have
checked the positioning of Q24 and it looks correct.  The right crystals are
installed at X3 and X4 and grounding the cases went smoothly, so I don't
think I overheated them.  I have reflowed the solder on the parts around the
BFO area.  A symptom that may or may not mean anything: the S-Meter is
showing S5.  It was properly adjusted back in Alignment and Testing Part I.
What should I do next?

 

Thanks for your ideas and suggestions.

 

73

Ken

K0WKM

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Re: K2 BFO problem

Don Wilhelm-4
Ken,

Did you obtain a good frequency reading when you did the PLL Reference
Oscillator test back on page 36?  If so, check the probe again by
putting the probe into either TP3 or TP1.  If you see a valid frequency
displayed, your probe is OK.

The most common problem builders have are soldering problems.  Re-flow
the soldering in the BFO  and U11 area with a hot soldering iron (750
deg/F).  Also check carefully for solder bridges.  Unfortunately, one
lead of both X3 and X4 are under the pad for L33, so ignore those for
the time being (if nothing else works, Lift one end of the resistor
securing L33 and re-flow the soldering at those leads).
Do you have near 8 volts at U11 pin 8?  Is U11 pin 1 and 2 close to 1.4
volts?  Do you have about 6 volts at U11 pin 6?

Touch the counter probe to U11 pin 6 (careful not to short to an
adjacent pin).  Do you have a valid frequency reading?  If you do, then
the BFO is working, and the problem is with Q24 and its associated
components.  Be certain you have mounted D36 (the SMT1B) part correctly,
and the soldering of Q24, RP6, R98, and R99 is good.

If still no progress, either assemble the parts provided in your K2 kit
for the RF Probe (schematic in Appendix E) or let us know that you have
an oscilloscope available.

73,
Don W3FPR

Ken Mohler wrote:

> Hi Gang -
>
>  
>
> I'm building my 2nd K2 and am at the point of Alignment and Test, Part II.
> All of the tests and alignment steps through the VCO alignment have been
> completed successfully.  Everything has been right in the center of the
> expected parameters.  Then I got to the BFO test.  I'm getting a reading of
> 0000.00.  Here's what I know so far:  D37 and D38 are the correct types and
> oriented properly.  I have measured the resistance across the resistor
> holding L33 down (or up?) and get a reading of 1.5 ohms, indicating to me
> that L33 is intact and effectively soldered to the resistor leads.  I have
> checked the positioning of Q24 and it looks correct.  The right crystals are
> installed at X3 and X4 and grounding the cases went smoothly, so I don't
> think I overheated them.  I have reflowed the solder on the parts around the
> BFO area.  A symptom that may or may not mean anything: the S-Meter is
> showing S5.  It was properly adjusted back in Alignment and Testing Part I.
> What should I do next?
>
>  
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Re: K2 BFO problem

John Fritze
In reply to this post by Ken Mohler
Ken,

Make sure you have your probe plugged into the correct jack.  Sounds
like what first happened to me, until I turned the rig around (back to
me) I forgot there were 2 jacks.  Probably not the problem, but hey,
you never know.

John
K2QY
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Re: K2 BFO problem

Ken Mohler
In reply to this post by Don Wilhelm-4
Don -

You have me on the right track.  I have a valid frequency reading at pin 6
of U11 and I can follow it back through L33 and C169 to the gate of Q24. The
waveform gets fuzzier and has lower amplitude past L33 (I do have a scope)
but is still countable at C169.  Past Q24 I don't have anything
recognizable.  I have reflowed the solder on everything around there.  D36
appears to be installed correctly. I don't have an extra J310 to swap out
Q24, but will get one if you think that's the next step.  BTW, I measured
the voltages at U11 and all are what you told me to expect except pin 8 is
around 6 volts.  Still, the BFO seems to be working, just not getting
anything as far as TP2.  Thanks for the help and please keep it coming.

73,
Ken
K0WKM

-----Original Message-----
From: Don Wilhelm [mailto:[hidden email]]
Sent: Friday, July 16, 2010 6:49 PM
To: Ken Mohler
Cc: [hidden email]
Subject: Re: [Elecraft] K2 BFO problem

Ken,

Did you obtain a good frequency reading when you did the PLL Reference
Oscillator test back on page 36?  If so, check the probe again by
putting the probe into either TP3 or TP1.  If you see a valid frequency
displayed, your probe is OK.

The most common problem builders have are soldering problems.  Re-flow
the soldering in the BFO  and U11 area with a hot soldering iron (750
deg/F).  Also check carefully for solder bridges.  Unfortunately, one
lead of both X3 and X4 are under the pad for L33, so ignore those for
the time being (if nothing else works, Lift one end of the resistor
securing L33 and re-flow the soldering at those leads).
Do you have near 8 volts at U11 pin 8?  Is U11 pin 1 and 2 close to 1.4
volts?  Do you have about 6 volts at U11 pin 6?

Touch the counter probe to U11 pin 6 (careful not to short to an
adjacent pin).  Do you have a valid frequency reading?  If you do, then
the BFO is working, and the problem is with Q24 and its associated
components.  Be certain you have mounted D36 (the SMT1B) part correctly,
and the soldering of Q24, RP6, R98, and R99 is good.

If still no progress, either assemble the parts provided in your K2 kit
for the RF Probe (schematic in Appendix E) or let us know that you have
an oscilloscope available.

73,
Don W3FPR

Ken Mohler wrote:
> Hi Gang -
>
>  
>
> I'm building my 2nd K2 and am at the point of Alignment and Test, Part II.
> All of the tests and alignment steps through the VCO alignment have been
> completed successfully.  Everything has been right in the center of the
> expected parameters.  Then I got to the BFO test.  I'm getting a reading
of
> 0000.00.  Here's what I know so far:  D37 and D38 are the correct types
and
> oriented properly.  I have measured the resistance across the resistor
> holding L33 down (or up?) and get a reading of 1.5 ohms, indicating to me
> that L33 is intact and effectively soldered to the resistor leads.  I have
> checked the positioning of Q24 and it looks correct.  The right crystals
are
> installed at X3 and X4 and grounding the cases went smoothly, so I don't
> think I overheated them.  I have reflowed the solder on the parts around
the
> BFO area.  A symptom that may or may not mean anything: the S-Meter is
> showing S5.  It was properly adjusted back in Alignment and Testing Part
I.
> What should I do next?
>
>  

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Re: K2 BFO problem

Don Wilhelm-4
Ken,

The "fuzzy" waveform on the 'scope is normal - but how much so is
difficult for me to say whether yours is normal or abnormal.

Check the value of C169 - it should be 390 pF (marked 391).

OK, the BFO is oscillating, so look at Q24 carefully - is it oriented
correctly?  If so, enter CAL FCTR and tap the BAND+ button while
measuring the voltage on the drain (see the schemastic key page if you
are not familiar with the pinout).  The voltage should go high(almost 8
volts), and then tap BAND- and the voltage should go nearly to zero.

Other things to check - look for a solder bridge between pins 1 and 2 of
U10;, check the SMT1B for correct orientation; re-check the orientation
of D36, and check the soldering of R98, C168, D36, R99 and SMT1B.

If all the above is correct, try replacing Q24.  If you have a J309
around, try that (if you have the KDSP2 kit, there are J309s in there).

73,
Don W3FPR


Ken Mohler wrote:

> Don -
>
> You have me on the right track.  I have a valid frequency reading at pin 6
> of U11 and I can follow it back through L33 and C169 to the gate of Q24. The
> waveform gets fuzzier and has lower amplitude past L33 (I do have a scope)
> but is still countable at C169.  Past Q24 I don't have anything
> recognizable.  I have reflowed the solder on everything around there.  D36
> appears to be installed correctly. I don't have an extra J310 to swap out
> Q24, but will get one if you think that's the next step.  BTW, I measured
> the voltages at U11 and all are what you told me to expect except pin 8 is
> around 6 volts.  Still, the BFO seems to be working, just not getting
> anything as far as TP2.  Thanks for the help and please keep it coming.
>
> 73,
> Ken
> K0WKM
>
> -----Original Message-----
> From: Don Wilhelm [mailto:[hidden email]]
> Sent: Friday, July 16, 2010 6:49 PM
> To: Ken Mohler
> Cc: [hidden email]
> Subject: Re: [Elecraft] K2 BFO problem
>
> Ken,
>
> Did you obtain a good frequency reading when you did the PLL Reference
> Oscillator test back on page 36?  If so, check the probe again by
> putting the probe into either TP3 or TP1.  If you see a valid frequency
> displayed, your probe is OK.
>
> The most common problem builders have are soldering problems.  Re-flow
> the soldering in the BFO  and U11 area with a hot soldering iron (750
> deg/F).  Also check carefully for solder bridges.  Unfortunately, one
> lead of both X3 and X4 are under the pad for L33, so ignore those for
> the time being (if nothing else works, Lift one end of the resistor
> securing L33 and re-flow the soldering at those leads).
> Do you have near 8 volts at U11 pin 8?  Is U11 pin 1 and 2 close to 1.4
> volts?  Do you have about 6 volts at U11 pin 6?
>
> Touch the counter probe to U11 pin 6 (careful not to short to an
> adjacent pin).  Do you have a valid frequency reading?  If you do, then
> the BFO is working, and the problem is with Q24 and its associated
> components.  Be certain you have mounted D36 (the SMT1B) part correctly,
> and the soldering of Q24, RP6, R98, and R99 is good.
>
> If still no progress, either assemble the parts provided in your K2 kit
> for the RF Probe (schematic in Appendix E) or let us know that you have
> an oscilloscope available.
>
> 73,
> Don W3FPR
>
> Ken Mohler wrote:
>  
>> Hi Gang -
>>
>>  
>>
>> I'm building my 2nd K2 and am at the point of Alignment and Test, Part II.
>> All of the tests and alignment steps through the VCO alignment have been
>> completed successfully.  Everything has been right in the center of the
>> expected parameters.  Then I got to the BFO test.  I'm getting a reading
>>    
> of
>  
>> 0000.00.  Here's what I know so far:  D37 and D38 are the correct types
>>    
> and
>  
>> oriented properly.  I have measured the resistance across the resistor
>> holding L33 down (or up?) and get a reading of 1.5 ohms, indicating to me
>> that L33 is intact and effectively soldered to the resistor leads.  I have
>> checked the positioning of Q24 and it looks correct.  The right crystals
>>    
> are
>  
>> installed at X3 and X4 and grounding the cases went smoothly, so I don't
>> think I overheated them.  I have reflowed the solder on the parts around
>>    
> the
>  
>> BFO area.  A symptom that may or may not mean anything: the S-Meter is
>> showing S5.  It was properly adjusted back in Alignment and Testing Part
>>    
> I.
>  
>> What should I do next?
>>
>>  
>>    
>
> ______________________________________________________________
> 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
>
>  
______________________________________________________________
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Re: K2 BFO problem

Ken Mohler
Don -

It gets weirder and weirder.  I did the test of the Q24 drain voltage.  When
I tapped Band+ I got 3.4V.  BAND- dropped to a little less than a volt.
Then I went on to check the following things you suggested.  Now here's
where it got weird... I went back to redo the Q24 drain voltage and now I
get around 0 volts no matter which BAND button I tap.  I didn't change
anything - honest!  I'm less convinced that the problem lies within Q24.
Perhaps Q24 is not getting the right signals from the other side.

My first K2 went together with nary a glitch, and I have been even more
deliberate and careful with this one.

If you still have the patience, suggest what I ought to do next.

73,
Ken
K0WKM

-----Original Message-----
From: Don Wilhelm [mailto:[hidden email]]
Sent: Saturday, July 17, 2010 7:57 PM
To: Ken Mohler
Cc: [hidden email]
Subject: Re: [Elecraft] K2 BFO problem

Ken,

The "fuzzy" waveform on the 'scope is normal - but how much so is
difficult for me to say whether yours is normal or abnormal.

Check the value of C169 - it should be 390 pF (marked 391).

OK, the BFO is oscillating, so look at Q24 carefully - is it oriented
correctly?  If so, enter CAL FCTR and tap the BAND+ button while
measuring the voltage on the drain (see the schemastic key page if you
are not familiar with the pinout).  The voltage should go high(almost 8
volts), and then tap BAND- and the voltage should go nearly to zero.

Other things to check - look for a solder bridge between pins 1 and 2 of
U10;, check the SMT1B for correct orientation; re-check the orientation
of D36, and check the soldering of R98, C168, D36, R99 and SMT1B.

If all the above is correct, try replacing Q24.  If you have a J309
around, try that (if you have the KDSP2 kit, there are J309s in there).

73,
Don W3FPR


Ken Mohler wrote:
> Don -
>
> You have me on the right track.  I have a valid frequency reading at pin 6
> of U11 and I can follow it back through L33 and C169 to the gate of Q24.
The

> waveform gets fuzzier and has lower amplitude past L33 (I do have a scope)
> but is still countable at C169.  Past Q24 I don't have anything
> recognizable.  I have reflowed the solder on everything around there.  D36
> appears to be installed correctly. I don't have an extra J310 to swap out
> Q24, but will get one if you think that's the next step.  BTW, I measured
> the voltages at U11 and all are what you told me to expect except pin 8 is
> around 6 volts.  Still, the BFO seems to be working, just not getting
> anything as far as TP2.  Thanks for the help and please keep it coming.
>
> 73,
> Ken
> K0WKM
>
> -----Original Message-----
> From: Don Wilhelm [mailto:[hidden email]]
> Sent: Friday, July 16, 2010 6:49 PM
> To: Ken Mohler
> Cc: [hidden email]
> Subject: Re: [Elecraft] K2 BFO problem
>
> Ken,
>
> Did you obtain a good frequency reading when you did the PLL Reference
> Oscillator test back on page 36?  If so, check the probe again by
> putting the probe into either TP3 or TP1.  If you see a valid frequency
> displayed, your probe is OK.
>
> The most common problem builders have are soldering problems.  Re-flow
> the soldering in the BFO  and U11 area with a hot soldering iron (750
> deg/F).  Also check carefully for solder bridges.  Unfortunately, one
> lead of both X3 and X4 are under the pad for L33, so ignore those for
> the time being (if nothing else works, Lift one end of the resistor
> securing L33 and re-flow the soldering at those leads).
> Do you have near 8 volts at U11 pin 8?  Is U11 pin 1 and 2 close to 1.4
> volts?  Do you have about 6 volts at U11 pin 6?
>
> Touch the counter probe to U11 pin 6 (careful not to short to an
> adjacent pin).  Do you have a valid frequency reading?  If you do, then
> the BFO is working, and the problem is with Q24 and its associated
> components.  Be certain you have mounted D36 (the SMT1B) part correctly,
> and the soldering of Q24, RP6, R98, and R99 is good.
>
> If still no progress, either assemble the parts provided in your K2 kit
> for the RF Probe (schematic in Appendix E) or let us know that you have
> an oscilloscope available.
>
> 73,
> Don W3FPR
>
> Ken Mohler wrote:
>  
>> Hi Gang -
>>
>>  
>>
>> I'm building my 2nd K2 and am at the point of Alignment and Test, Part
II.

>> All of the tests and alignment steps through the VCO alignment have been
>> completed successfully.  Everything has been right in the center of the
>> expected parameters.  Then I got to the BFO test.  I'm getting a reading
>>    
> of
>  
>> 0000.00.  Here's what I know so far:  D37 and D38 are the correct types
>>    
> and
>  
>> oriented properly.  I have measured the resistance across the resistor
>> holding L33 down (or up?) and get a reading of 1.5 ohms, indicating to me
>> that L33 is intact and effectively soldered to the resistor leads.  I
have

>> checked the positioning of Q24 and it looks correct.  The right crystals
>>    
> are
>  
>> installed at X3 and X4 and grounding the cases went smoothly, so I don't
>> think I overheated them.  I have reflowed the solder on the parts around
>>    
> the
>  
>> BFO area.  A symptom that may or may not mean anything: the S-Meter is
>> showing S5.  It was properly adjusted back in Alignment and Testing Part
>>    
> I.
>  
>> What should I do next?
>>
>>  
>>    
>
> ______________________________________________________________
> 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
>
>  

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Re: K2 BFO problem

Don Wilhelm-4
Ken,

You are likely chasing a bad solder connection - things that change by
themselves is usually an indication of a solder problem.
You are getting close if it was the Q24 drain voltage changing.  Check
RF Board R98, and then go to the Control Board and check the components
shown on the Control Board schematic area marked "ALC" (at the top of
the page).  Double-check the position of the components soldered on the
back of the board.   When in CAL FCTR, tapping BAND+ should result in a
high voltage on the VALC line, and tapping BAND-, it should drop to
zero.  Don't forget to check the connectors between the Control Board
and the RF Board.

73,
Don W3FPR

Ken Mohler wrote:

> Don -
>
> It gets weirder and weirder.  I did the test of the Q24 drain voltage.  When
> I tapped Band+ I got 3.4V.  BAND- dropped to a little less than a volt.
> Then I went on to check the following things you suggested.  Now here's
> where it got weird... I went back to redo the Q24 drain voltage and now I
> get around 0 volts no matter which BAND button I tap.  I didn't change
> anything - honest!  I'm less convinced that the problem lies within Q24.
> Perhaps Q24 is not getting the right signals from the other side.
>
> My first K2 went together with nary a glitch, and I have been even more
> deliberate and careful with this one.
>
> If you still have the patience, suggest what I ought to do next.
>
> 73,
> Ken
> K0WKM
>
> -----Original Message-----
> From: Don Wilhelm [mailto:[hidden email]]
> Sent: Saturday, July 17, 2010 7:57 PM
> To: Ken Mohler
> Cc: [hidden email]
> Subject: Re: [Elecraft] K2 BFO problem
>
> Ken,
>
> The "fuzzy" waveform on the 'scope is normal - but how much so is
> difficult for me to say whether yours is normal or abnormal.
>
> Check the value of C169 - it should be 390 pF (marked 391).
>
> OK, the BFO is oscillating, so look at Q24 carefully - is it oriented
> correctly?  If so, enter CAL FCTR and tap the BAND+ button while
> measuring the voltage on the drain (see the schemastic key page if you
> are not familiar with the pinout).  The voltage should go high(almost 8
> volts), and then tap BAND- and the voltage should go nearly to zero.
>
> Other things to check - look for a solder bridge between pins 1 and 2 of
> U10;, check the SMT1B for correct orientation; re-check the orientation
> of D36, and check the soldering of R98, C168, D36, R99 and SMT1B.
>
> If all the above is correct, try replacing Q24.  If you have a J309
> around, try that (if you have the KDSP2 kit, there are J309s in there).
>
> 73,
> Don W3FPR
>
>
> Ken Mohler wrote:
>  
>> Don -
>>
>> You have me on the right track.  I have a valid frequency reading at pin 6
>> of U11 and I can follow it back through L33 and C169 to the gate of Q24.
>>    
> The
>  
>> waveform gets fuzzier and has lower amplitude past L33 (I do have a scope)
>> but is still countable at C169.  Past Q24 I don't have anything
>> recognizable.  I have reflowed the solder on everything around there.  D36
>> appears to be installed correctly. I don't have an extra J310 to swap out
>> Q24, but will get one if you think that's the next step.  BTW, I measured
>> the voltages at U11 and all are what you told me to expect except pin 8 is
>> around 6 volts.  Still, the BFO seems to be working, just not getting
>> anything as far as TP2.  Thanks for the help and please keep it coming.
>>
>> 73,
>> Ken
>> K0WKM
>>
>> -----Original Message-----
>> From: Don Wilhelm [mailto:[hidden email]]
>> Sent: Friday, July 16, 2010 6:49 PM
>> To: Ken Mohler
>> Cc: [hidden email]
>> Subject: Re: [Elecraft] K2 BFO problem
>>
>> Ken,
>>
>> Did you obtain a good frequency reading when you did the PLL Reference
>> Oscillator test back on page 36?  If so, check the probe again by
>> putting the probe into either TP3 or TP1.  If you see a valid frequency
>> displayed, your probe is OK.
>>
>> The most common problem builders have are soldering problems.  Re-flow
>> the soldering in the BFO  and U11 area with a hot soldering iron (750
>> deg/F).  Also check carefully for solder bridges.  Unfortunately, one
>> lead of both X3 and X4 are under the pad for L33, so ignore those for
>> the time being (if nothing else works, Lift one end of the resistor
>> securing L33 and re-flow the soldering at those leads).
>> Do you have near 8 volts at U11 pin 8?  Is U11 pin 1 and 2 close to 1.4
>> volts?  Do you have about 6 volts at U11 pin 6?
>>
>> Touch the counter probe to U11 pin 6 (careful not to short to an
>> adjacent pin).  Do you have a valid frequency reading?  If you do, then
>> the BFO is working, and the problem is with Q24 and its associated
>> components.  Be certain you have mounted D36 (the SMT1B) part correctly,
>> and the soldering of Q24, RP6, R98, and R99 is good.
>>
>> If still no progress, either assemble the parts provided in your K2 kit
>> for the RF Probe (schematic in Appendix E) or let us know that you have
>> an oscilloscope available.
>>
>> 73,
>> Don W3FPR
>>
>> Ken Mohler wrote:
>>  
>>    
>>> Hi Gang -
>>>
>>>  
>>>
>>> I'm building my 2nd K2 and am at the point of Alignment and Test, Part
>>>      
> II.
>  
>>> All of the tests and alignment steps through the VCO alignment have been
>>> completed successfully.  Everything has been right in the center of the
>>> expected parameters.  Then I got to the BFO test.  I'm getting a reading
>>>    
>>>      
>> of
>>  
>>    
>>> 0000.00.  Here's what I know so far:  D37 and D38 are the correct types
>>>    
>>>      
>> and
>>  
>>    
>>> oriented properly.  I have measured the resistance across the resistor
>>> holding L33 down (or up?) and get a reading of 1.5 ohms, indicating to me
>>> that L33 is intact and effectively soldered to the resistor leads.  I
>>>      
> have
>  
>>> checked the positioning of Q24 and it looks correct.  The right crystals
>>>    
>>>      
>> are
>>  
>>    
>>> installed at X3 and X4 and grounding the cases went smoothly, so I don't
>>> think I overheated them.  I have reflowed the solder on the parts around
>>>    
>>>      
>> the
>>  
>>    
>>> BFO area.  A symptom that may or may not mean anything: the S-Meter is
>>> showing S5.  It was properly adjusted back in Alignment and Testing Part
>>>    
>>>      
>> I.
>>  
>>    
>>> What should I do next?
>>>
>>>  
>>>    
>>>      
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>>    
>
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Re: K2 BFO problem

Ken Mohler
You were right, Don, as usual.  The problem was an unsoldered point on the
control board. I was looking on the wrong board the whole time. All tests
and adjustments on Part II are complete and I'm moving forward.  Thanks for
all the help!

Ken
K0WKM

-----Original Message-----
From: Don Wilhelm [mailto:[hidden email]]
Sent: Monday, July 19, 2010 9:06 AM
To: Ken Mohler
Cc: [hidden email]
Subject: Re: [Elecraft] K2 BFO problem

Ken,

You are likely chasing a bad solder connection - things that change by
themselves is usually an indication of a solder problem.
You are getting close if it was the Q24 drain voltage changing.  Check
RF Board R98, and then go to the Control Board and check the components
shown on the Control Board schematic area marked "ALC" (at the top of
the page).  Double-check the position of the components soldered on the
back of the board.   When in CAL FCTR, tapping BAND+ should result in a
high voltage on the VALC line, and tapping BAND-, it should drop to
zero.  Don't forget to check the connectors between the Control Board
and the RF Board.

73,
Don W3FPR


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