JT,
Use a fully insulated tuning tool - both ends of the trimmer cap are
floating above ground, so you will see a lot of 'hand capacitance'
effects with a metallic screwdriver. If you can achieve a null below 9
or 10, that is a normal low value.
Tune slowly and you can obtain the null. If you have a high impedance
input analog reading meter, you can do it easier than the 'no tools'
manual method. Connect your meter from the hot side of R2 to ground and
tune the cap for a minimum reading - the null is easier to see on an
analog meter - just tune for the smallest voltage, then check the value
displayed on the K2 - if it is less than 10, all is good.
If you cannot achieve a decent null, then you may have a significant
amount of residual inductance or capacitance in the KAT2 - usually due
to a non-operating relay. If that is the case, first inspect the
soldering on each of the relays (yes, you will have to lift some
inductors to do that) to be certain all pins are soldered.
73,
Don W3FPR
JT Croteau wrote:
Folks,
I am having a hard time doing the Bridge Null Adjustment (C55) on the
KAT2. The display reads HI pretty much continuously as I adjust C55.
However, every once and awhile it will flicker a number while I am
turning C55 but this is inconsistent. Before installing R6, you are
to also check U4 pin 1 voltage during tune. I am showing 4.61V at
this spot. I have checked, and rechecked T1 multiple times and do not
see any problems. I also don't see any cold solder joints.
However, is it possible to installed C55 the wrong way? The manual
wasn't specific on this like it was when installing variable caps
during K2 assembly.
Thanks
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