In article .com, "dick
on the langwang" wrote:

Has anyone experience of repairing moving coil meters and/or able give
me to any useful pointers. One of my (many !!) restoration projects is
being held up by an u/s meter & from inspection I suspect although the
coil/pointer move freely one of the fine wire connections to the coil
has gone open circuit, due to corrosion. I'm happy stripping down &
repairing clocks but have no experience of doing the same to meters. In
the end I'll probably have to find a replacement but it would be nice
to try & get the original meter working again.

Dick-

As I recall, current is conducted via upper and lower springs, to the
moving coil. If you can determine that the coil itself is still
conducting, you may be able to repair connections to the other components.

If the needle cannot be zeroed with the mechanical adjustment, it is
possible one of the springs has broken or come loose at one end.

It would be handy if you have an Ohmmeter with a beeper, that sounds with
very low current conduction.

(I've had very few movements with open coils, but have obversed several
cases where plating of the pole pieces peeled and jammed the movement.)

As far as replacement, look near the bottom of the meter scale. You may
find the meter sensitivity listed. It might be something like "FS=1mA" or
"FS=50uA". If you determine the sensitivity, any meter with the same size
and sensitivity may be useable by swapping meter scales.

Fred
K4DII

Already know the sensitivity (250 microamps) but thanks for the tip
about peeling pole piece plating, don't think it's that though because
the coil/needle rotate freely. Reason I suspect the o/c is because
there's a 'green, furry blob' (due damp storage sometime in the past ?)
halfway along the fine coil connection wire, possibly surrounding a
joint. Job for a fine brush & steady hand I think !!