[Elecraft] KAT2 problem.

[John Webster]

I need your help, once again!

All construction and tests have been fine up to
the Bridge Null Adjustment (C55) on page 16
Rev D KAT2 Manual.

I get erratic readings on the LCD at 5w while in
TUNE.  At times in adjustment I can get it to read 
10 or below, but it keeps varying all over the place
and not only when the screwdriver is adjusting the
trimmer.

Also, (as a result?) I cannot get more than .25 volts
on U4 pin 1 (page 17 step 4) on transmit.  Rx voltage
is 0 as it should be.

Note: I do not have a dummy load (that was a 
dummy move), but have a MFJ 259B Antenna 
Analyzer and use it to adjust my Match Box antenna
tuner (with long wire out of it) to exactly 1:1 SWR and
a verified resistive 50 ohms at the frequency in use
(empty spot at 7.120).

1. Since I can get to be more or less stable at a
2w power setting, I suspected RF getting into the
works.  I moved the whole setup 20 feet away from
tuner and antenna.  Readjusted for 50 ohms at the rigs
Ant1 connector.  No difference.  Cannot find a 
stable setting at 5w.

2. Took KAT2 apart.  Checked T1 (toroid wound by
Toroid Guy), redid the solder joints on it and all other
components in the Bridge circuit.  Can't find any 
problem.  Results same. J7 is oriented correctly.

Any helpful suggestions would be gratefully received.
My (limited) understanding of the circuit keeps coming
back to something wrong at T1 but I might be missing
something else.

[Now I regret my wasted energy posting silliness about 
lockwashers yesterday!]

73

John, N6JW