[R-390] Autopsy of a bad PTO.

[Phil Atchley]

Hi.
Hi.
Since there is another PTO coming I went ahead and took this one apart =
all
the way down to the corrector disk to see if I could determine the =
failure
mode (not sure I can get it back together correctly 8^)  Anyway, I was
right.  The 48 tuning screws are rotated one by one past a round spring
loaded thingy made of spring steel that has a small piece of steel that
looks kind of like a "footbridge" spot welded to it.  As the screw for a
particular segment of the frequency range (25 KHz steps) walks over the
"footbridge" it presses down on it and pushes the slug under it further =
into
the coil. =20

The "footbridge" was damaged in two ways.  First it had a BIG dent in it =
on
one side that would make screws riding on that side of the bridge =
(they're
staggered) not press down as hard on the bridge. Secondly, the spot weld
that holds one end of the bridge is broken loose so that it has lost =
some of
its "stiffness" and positive action.

In trying to fix the "dent" in the bridge I'm afraid that I also =
weakened it
some more as spring steel doesn't take kindly to dents and trying to
straighten them out. =20

The third problem I found was that some of the screws had apparently =
been
turned "counterclockwise" too hard, spreading the slot and screw too =
wide to
thread down into the disk far enough to reach the damaged bridge.  These =
are
the culprits that probably had no adjustment affect as they wouldn't =
reach
the "footbridge".  These are very tiny screws that are really only a =
screw
shaft with a "slot" in the end and a flat head on the backside to "walk
across the bridge". =20

NOTE:  A couple articles that I read said that there was a flexible =
Teflon
ring that these screws rode on forming kind of a cam.  This one had no =
such
ring, only the spring steel thingy that the screw heads walked across.   =


73 de Phil, KO6BB

****************************************************
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