Hi, Paul!
Sounds like a tiny metal burr is shorting the case of Q6 to ground.
These are almost always at the screw hole. Check the following:
1. Make sure the screw itself is plastic; Elecraft will send you a
new one free if it isn't.
2. Pull off the insulated pad and use an Xacto knife from the inside
of the cover to "circle" (swirl around at a 45 deg angle) the Q6
mounting hole and remove any burrs.
3. Using fine sandpaper, sand the area inside the case that the
insulated pad covers to ensure it is perfectly flat, especially
around the screw hole.
Replace the insulated pad and reassemble. Very smart of you to use an
ohm meter to alert you of potential smoke inhalation during power-up.
Brian - W6FVI
Paul T. Rubin wrote:
Hello all:
I had disassembled my previously operational KX1 (SN854) in anticipation of
adding the KXB3080 option. However I realized that it would be some time
before I could get around to it, and I felt like operating. So I put it
back together, powered it up, and released the smoke. Examination showed
that a short section of V+ PCB trace just after the power switch had
vaporized. PCB traces make excellent fusible links. I measured the
resistance to ground from the far end of the trace. It was 1025 Ohms. By
now I had a pretty good idea what was going on. I repaired the trace, and
measured the same resistance at the power connector. So far so good. I
powered it up outside of the case and all is well. Now I'm real sure what's
going on. I reassembled it into the case, and measured the resistance at
the power connector; 0.4 Ohms. Q6 was shorted to the case. I backed off the
screw for Q6 1/8 of a turn and the short goes away. I examined the plastic
spacer and it does not seem deformed. The insulating pad also seems fine.
I did not torque the screw to 20 foot pounds. I don't know what to do next.
All suggestions appreciated.
Thanks,
Paul N8NOV
Houston
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