[Elecraft] vexing K3 transverter problem solved

[Edward R Cole]

Lew,

Excellent observation (and troubleshooting).

Too often a problem can be due to something very simple but 
unnoticed.  If you build kits (the kind you solder components to a pc 
board) you may have noticed many holes place in strategic areas of 
the board that have no components installed thru them.  They are call 
via's and are place to ground the circuit board to avoid sneak paths 
for currents that can cause sporadic oscillation in the 
circuit.  Often there are more screws holding down a board than just 
at the corners and they also help proper grounding.  A lose screw or 
board can lead to very strange operating characteristics.  This issue 
gets rapidly more complicated designing for VHF and higher 
frequencies, but can cause issues even in audio stages.

This "magic" that good RF designers have is what you pay more for.

73, Ed - KL7UW
my first job out of college was as Technician in a small R&D 
engineering dept.  Our job was to build up design prototypes from the 
engineers initial design and test them for proper operation - which 
they typically did not do.  Then we searched for some of those magic 
little "fixes" to the real circuit that did not show in the 
schematic.  Many rerouting of circuits and bypass capacitors and RF 
chokes are placed as result of this type of "fine tuning" of a 
design.  Your alpha tester do this.

------------------
Date: Wed, 7 Jan 2015 18:50:00 -0800
From: Lewis Phelps <lew at n6lew.us>
To: "elecraft at mailman.qth.net List" <elecraft at mailman.qth.net>
Subject: [Elecraft] vexing K3 transverter ptoblem solved
Message-ID: <A066DF1D-70C0-4433-8FDD-7D9E6AC34D25 at n6lew.us>
Content-Type: text/plain;       charset=utf-8

For what it?s worth, I thought I would pass along my recent 
experience with a vexing transverter problem, and the cause of the 
problem that I eventually identified.

The issue was that my XV432 would light up its power output 
LEDs  ever so briefly when the transmitter was keyed, and then shut 
down. It was pretty obviously a shorted output situation.

I first assumed it was a faulty coax cable connecting either the K3 
to the XV432 or the SV4 32 to the antenna. So I substituted different 
cables all the way around, with no benefit.

I even tested the hypothesis that the dummy load had gone bad, and 
substituted an older and smaller dummy load. Still no joy.

About the only thing left in the chain between the K3 and the XV432 
was the KXV3 transverter I/O board. Upon initial inspection, I saw 
that it was wobbling back and forth about 1/4?.  Upon closer 
inspection (requiring removal of the side panel of the case) it 
became clear that a 1/2? long 4-40 machine screw was missing, 
allowing the board to flex backward and forward, and apparently 
shorting the output.

I replaced the missing machine screw, tightened the other machine 
screw on the opposite corner of the I/O board, and the problem was gone.

Moral to the story:  mechanical problems can cause electrical problems.

At least I got it fixed in time for the upcoming VHF contest.

73,

Lew

Lew Phelps N6LEW
Pasadena, CA DM04wd
Elecraft K3-10
Yaesu FT-7800
Lew at N6LEW.US
www.n6lew.us


73, Ed - KL7UW
http://www.kl7uw.com
     "Kits made by KL7UW"
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