pa4tim at gmail.com
Thu Apr 28 17:03:43 UTC 2011
I have removed one switch. I have measured the resistance at 500V from
the (cleaned) original material and that was much lower as a same lenght
of teflon. (but the Teflon was very hard to measure, if I came closer
then a meter to the HP4329A the meter jumped around, the needle was
almost max left in the most upper range at 1000V so we are talking
penta-ohms, I'm not only a volt-nut ;-) ).
So I made out of teflon a shaft-to-rotor coupler. A hell of a job. took
me two hours milling and turning the lath but then it fitted like a
glove. Then I made 12 teflon studs. I drilled a 4mm hole and with a
little tool I made I could press in the old inserts. The switch is
already in its place.
But I noticed a strange thing. The stud that was broken in to pieces was
hard and brittle. One insert was still in but just a little hit with a
screwdriver and it broke in two.
The other stud was still in one piece. But I did not want to take a risk
so i thought, lets replace this one too. I gave it a gentle hit but
nothing, took a pair of pliers squeezed as hard as I could, nothing.
even with a cutter, it just left bitemarks but no breaking. After all
this violence I had to replace it but I think there was nothing wrong
with this one. I heated it and then I could pull the inserts out.
So this is weird, almost all studs are gone to dust but some are as
strong as new. The problem is, to test it I have to use force and that
weakens them so I exchange them all to be shure.
But making 5 extra new rotors is a hell of a job so I will check the
rotor couplers optical very careful for cracks and leave them. The
reason the studs break when the plastic get hard is because the inserts
are a bit conical so screwing in the bold expands them. So there is
tension in the material. The rotor couplers are just a "lose" fit and if
one breaks I now know how to replace them. Not much work. The broken
coupler was coupled to a floating one rotorswitch (both studs complete
lose) so maybe a shock during transport.
I also mailed Fluke here in the Netherlands. Got a mail back from the
service desk they forwarded it to the service manager. If they can
supply new rotors and studs (affordable) that is even better, I like it
to be original.
Now I am going to find out if there is a affortable solution to
calibrate and adjust the 731A. I spoke someone who had a Tek current
scope probe calibrated and adjusted, That was allmost 500 euro. To much
After that I can compare them with my Guildline. (if I remember well the
10V is not adjustable but I have the manual so I will look that up
Chuck Harris schreef op do 28-04-2011 om 10:36 [-0400]:
> The only real way to tell with plastics is to subject them to the test
> of time and environment. The basic problem is one of plasticizer migration.
> Many plastics have an added goo that improves the way they flow in molding,
> and softens the plastic so that it is suitable for use. The plasticizer
> evaporates slowly out of the plastic making it shrink, and leaving it very
> brittle. Some plasticizers migrate to the surface leaving the plastic very
> sticky... vinyl (PVC), particularly soft vinyl, which is heavy in plasticizer,
> has that problem. That plasticizer migration is what makes xerox'd pages
> stick to vinyl binders, leaving the lettering behind on the vinyl...
> Some of the ancient plastics aren't really plastic at all... bakelite is an
> example.... and they hold up incredibly well. The common characteristic,
> in my opinion, no plasticizer. The much fabled BPA is one of the plasticizers
> that causes problems if it isn't used just right.... It also causes breast
> development in men, but that is another story.
> -Chuck Harris
> Marvin E. Gozum wrote:
> > Is there a way to decipher plastics potential longevity in a finished
> > product?
> > I'm impressed plastic parts on many HP equipment endure intact over 20+
> > years, some barely discoloring. I can't tell what type they are, but the
> > more durable plastics often feel hefty and solid. Likewise, Fluke DMM
> > have the same 'feeling' and endure for decades.
> > On a side note, casing of some iPhones barely 2-3 years old are
> > spontaneously cracking, so it can be made quite badly too.
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