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Here are 3 of my 4 P6139A
scope probes. These are all about 14 years old, and for most of that time
they have been plugged into a TDS540 scope. No interesting chemicals in
the area. All have various levels of crumbling and cracks. Merely touching
the white plastic makes it crumble, with a consistency reminiscent of chalk.
This seems to only apply to the thin cylinder of the plastic, the remainder
seems to not be ready to fall apart. As can be seen on the center
example, all the insulator has fallen out, the one on the right is partially
damaged, and the one on the left has cracks in it but I have been very
careful not to touch it. |
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Here is the middle BNC from
the above picture after dissasembly. |
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Here is the insulator from
the BNC on the right in the first picture |
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With a lot of careful measurements,
this is what I think the insulator dimensions should be. This was about
2 hours work.
Here are the dimensions for the external diameters from left to right
for the X axis: 0.165, 0.035, 0.120, 0.162, 0.268 and the respective
diameters are 0.272, 0.327, 0.288, 0.270,0.255
The internal diameters from left to right are: 0.400, .060 (implied), 0.255
and the respective diameters are 0.120, 0.052, 0.201
Procedure:
From the right end drill with #55 0.500, do not drill the 0.201 till later.
Do all outside surfaces. Now drill 0.201 with #7 drill. Touch the end of
the drill to the end of the work, and enter 0.280
Part off and with a little force, the 0.255 end should fit in a 0.250 collet.
Center drill and drill 0.120 with #31 total depth including drill tip 0.400
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With a few hours of work
I had 4 blank pieces of Teflon ready. A .5 inch stub at one end will go
into the lathe collet, and the rest is turned down to .4 inch diameter.
My first attempt at making a replacement failed, and the resulting scrap
are the two pieces on the right. 3 more to go with a bit more care. |
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First, drill a hole .052
diameter into the piece. This is the clearance for the center pin, and
will also be used for support from the tailstock through the rest of the
opperations (what I failed to do on my first attempt) |
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Checking setup to make sure
the cutting tool is at exactly the right height. Then do the first cut
brings it down to .327 inch, which is the outer diameter of the thin (.035)
triagular wedge (collar) that seats against the compensation box threaded
section (see second picture above). Haven't screwed up yet. |
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Second cut (.288) is one
of three diameters for the part of the insulator that goes into the BNC
housing. |
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Third and fourth cut finish
the outer surface for the section that goes into the BNC housing. |
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Now I am cutting the section
that goes into the threaded part of the compensation box. Then the diagonal
cut on the collar on the side that faces the BNC housing.
Next, carefully drill the
large hole for the BNC end, then separate the part from the stub, and drill
the compensation box end. This is the point where I broke my first attempt. |
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Here is a view of the new
part and the old damaged part |
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This is looking into the
BNC end |
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A side view of the finished
part |
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This is the compensation
box end of the insulator. The middle pin of the BNC plug only touches the
Teflon for a short distance at the narrow neck inside the insulator |
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Installed the new part.
What luck, it fits perfectly. |
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All assembled and ready
for use again. |