K2 Phase One Alignment Problem

[alan latz]

I need help with the 1st phase of alignment on a K2, s/n 6780. Everything
works perfectly with the exception of the Setting of the AGC Threshold
voltage on U2, pin 5.
I can only get a voltage of 3.62 volts with the R1 trimmer cap turned to
it's max ccw. The manual calls for 3.8 volts and I assume with the trimmer
set less than full ccw.
With a regulated power supply set at 12.51v, I get 12.33 going into 8v
regulator and 7.59 coming out.
Both oscillators are running as shown by Heatkit IM-2420 digital freq ctr.
X1 at 5.086 ant X2 at 3999.99.
U2 Pin voltage follows:1 @3.1, 2 @3.1, 3 @ 3.1, 4 @ 0.0, 5 @ 3.62, 5 @ 3.62,
6 @ 3.62, 7 @ 3.62 and 8 @ 7.59.

Perhaps this is not a problem. With all the K2's built, I wonder If I'm the
only one to encounter this problem.
I have examined all solder joints and redone any that were not good and
bright. I find no improper installed items. I checked the trimmer R1 and it
operates within it's range of 5.1K ohms.
I'm going to search for a "return to factory default" input in case I have
screwed up the controller with some wierd setting.

I have a Hayko 808 on order so I have no capability of desoldering any
componets at this point.

Thanks for any sugestions ahead of time.

Alan Latz KA9UCP
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[Don Wilhelm-4]

Alan,

You are not the only one.

The 8 volt regulator is on the low side of its spec.  That will cause no
problem other than you will not be able to adjust the AGC Threshold to
3.8 volts.  The 3.8 volt point is only valid if the 8 volt regulator is
really 8 volts.  When the 8 volt supply is lower than 8 volts, the AGC
Threshold can (and should) be a bit lower than 3.8 volts.  Just set the
AGC Threshold pot for maximum and all will be well.

If you find later that you need to increase the AGC Threshold voltage
(that is not likely), you can add a resistor in parallel with  the  
resistor in RP6 between pins 3 and 4 to bring the AGC Threshold voltage
a bit higher - a 10k resistor will usually suffice.

73,
Don W3FPR

alan latz wrote:

> I need help with the 1st phase of alignment on a K2, s/n 6780. Everything
> works perfectly with the exception of the Setting of the AGC Threshold
> voltage on U2, pin 5.
> I can only get a voltage of 3.62 volts with the R1 trimmer cap turned to
> it's max ccw. The manual calls for 3.8 volts and I assume with the trimmer
> set less than full ccw.
> With a regulated power supply set at 12.51v, I get 12.33 going into 8v
> regulator and 7.59 coming out.
> Both oscillators are running as shown by Heatkit IM-2420 digital freq ctr.
> X1 at 5.086 ant X2 at 3999.99.
> U2 Pin voltage follows:1 @3.1, 2 @3.1, 3 @ 3.1, 4 @ 0.0, 5 @ 3.62, 5 @ 3.62,
> 6 @ 3.62, 7 @ 3.62 and 8 @ 7.59.
>
> Perhaps this is not a problem. With all the K2's built, I wonder If I'm the
> only one to encounter this problem.
>  
>

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Please help support this email list: http://www.qsl.net/donate.html