K2 Internal ATU calibration issue

[Earl Richardet]

I've just completed the build on my internal K2 ATU.  I'm at the point of
performing the CALn Bridge Null Adjustment.  Following the procedures I am
unable to get any result other than "HI" unless I turn the power practically
down to zero.  Turning the power to zero I can get a reading close to 020.
However changing C55 doesn't lower or raise the indication.   I don't think
that the circuit is working as intended.  The voltage on pin 1 of U4 is
approx. 4.5 volts. With R6 removed.

 

I've looked over the components a number of times.  I've confirmed that all
the components in the circuit are the correct values, correctly soldered and
in the correct orientation.  Including L1.

 

Suggestions?

 

 

 

 

 

 

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[Don Wilhelm-4]

Earl,

The most likely cause is that T1 is not installed correctly - leads not
in the proper holes, leads not well stripped and tinned.

Of course, there are other possibilities as well - a relay pin not
soldered on the L/C board, an inductor or capacitor on the L/C board
that is somehow in the circuit.

To eliminate the L/C board from consideration, you can put a long jumper
between J4 pin 2 and J5 pin 15 (next to the last pins of the two
connectors) and try doing the bridge null adjustment (connect only to
ANT1).  If you can null the bridge with the jumper in place, the problem
is on the L/C board, but if you still cannot find a null with the jumper
in place, the problem is with T1, D1, D2, R1, R2, R3, R4, C50, C51, C52,
C53, C54, or C55.

73,
Don W3FPR

On 2/24/2012 3:17 AM, Earl Richardet wrote:

> I've just completed the build on my internal K2 ATU.  I'm at the point of
> performing the CALn Bridge Null Adjustment.  Following the procedures I am
> unable to get any result other than "HI" unless I turn the power practically
> down to zero.  Turning the power to zero I can get a reading close to 020.
> However changing C55 doesn't lower or raise the indication.   I don't think
> that the circuit is working as intended.  The voltage on pin 1 of U4 is
> approx. 4.5 volts. With R6 removed.
>
>
>
> I've looked over the components a number of times.  I've confirmed that all
> the components in the circuit are the correct values, correctly soldered and
> in the correct orientation.  Including L1.
>
>
>
> Suggestions?
>
>
>
>
>
>
>
>
>
>
>
>
>
> ______________________________________________________________
> 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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