K2 building problem

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K2 building problem

Gary Auchard
I've just finished the assembly of part 2 on the RF board and ran into a BFO problem during the testing on page 65 of the manual.  All other tests have been right on the money to this point.
 
When testing in the frequency counter mode the front display is changing rapidly when using the frequency counter probe inserted in TP2.  If I tap the Band- button the display locks in at 4.91253.  When I tap the Band+ button the display goes back to changing rapidly.
 
I can measure a good solid reading at pin 6 of U11 telling me the BFO is working and the frequency displayed is 4.91253.
 
I cannot get a reading for the BFO High Frequency.  I've checked L33 and it's fine with no short caused by R116 being on top of it and has a good continuity across the windings.
 
X3 and X4 are the correct crystals for that location and came from the package marked 4.91 MHZ.
 
Anyone have an idea what the problem might be?
 
Gary Auchard - WB0MNA
K2 sn. 6506

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Re: K2 building problem

Don Wilhelm-4
Gary,

The frequency display changing rapidly is an indicator of one of 2 things.
1) The BFO oscillation is stopping, or
2) The BFO signal is too weak to be displayed properly by the counter.

I would suggest that you check the soldering at X3, X4, C173.C174. RP6,
D37 and D38, Q24, D36, R98, R99.  Reflow the soldering with a hot iron
(750 to 800 deg F) if necessary.

73,
Don W3FPR

Gary Auchard wrote:

> I've just finished the assembly of part 2 on the RF board and ran into
> a BFO problem during the testing on page 65 of the manual.  All other
> tests have been right on the money to this point.
>  
> When testing in the frequency counter mode the front display is
> changing rapidly when using the frequency counter probe inserted in
> TP2.  If I tap the Band- button the display locks in at 4.91253.  When
> I tap the Band+ button the display goes back to changing rapidly.
>  
> I can measure a good solid reading at pin 6 of U11 telling me the BFO
> is working and the frequency displayed is 4.91253.
>  
> I cannot get a reading for the BFO High Frequency.  I've checked L33
> and it's fine with no short caused by R116 being on top of it and has
> a good continuity across the windings.
>  
> X3 and X4 are the correct crystals for that location and came from the
> package marked 4.91 MHZ.
>  
> Anyone have an idea what the problem might be?
>  
> Gary Auchard - WB0MNA
> K2 sn. 6506
>
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