Hi Steve,
> Any hints for a pointer than hangs up periodically?
I assume you're satisfied that the problem is with the meter, not the circuit
sending it a naughty current. I'm also assuming it's a moving coil meter.
Three suggestions. Apologies if you're already thought of them, and if they're
teaching grandmother to suck eggs.
1. Needle bent, scraping on the plastic/glass or on the scale.
Cure: dismantle meter and bend pointer gently back.
2. Bearings either too tight or (possibly) too slack.
Cure: dismantle and examine the bearings at each end, the ones the rectangular
coil pivots in. With posh meters, you sometimes find that one of these can be
adjusted by screwing it in or out. Patience may be needed to find the best
setting. There may be a lock nut.
3. Grit (especially metal filings) in the works. This can get between the
moving coil and the pole-pieces it rotates within.
Cure: (you've guessed it) dismantle and clean out.
If the muck is magnetic (e.g. iron/steel), try to wipe it along the magnet away
from the poles and towards the middle(ish) of the magnet, where you have some
chance of pulling the bits off. This can be an extremely finicky and
aggravating job.
If the muck is non-magnetic, I suppose just brush or blow it out - I've never
been lucky enough to have non-magnetic muck ;-(
Two big words of warning:
Meters are v-e-r-y delicate, especially the coil springs that return the
pointer to zero. The reason I now dismantle them with confidence (though also a
sinking feeling) is that I wrecked a couple in my teens, and learnt the hard
way.
I've given myself frequent problems dismantling meters on my workbench - in
fact, doing so has probably been the main reason for having to clean them!
The problem is that my workbench has plenty of bits of steel and iron lying
around: filings from things I've made/sawn/filed/etc. over the years.
Dismantled meters are a very good way of cleaning it up! The muck jumps to the
strong magnets of a meter with evident glee. I would suggest dismantling the
meter somewhere else, e.g. on a dining room table.
Good luck!
Chris G4OKW
-----------------------------
Dr Chris Trayner
School of Electronic & Electrical Engineering,
The University of Leeds,
Leeds LS2 9JT, United Kingdom
Tel: +44 113 34 32053
Fax: +44 113 34 32032
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