Scherrer Instruments on Manchester in St. Louis or a suburb, used to do
meter movements. But the last time I wished a fix for a broken taut band
movement, it proved years faster and cheaper to buy a new movement than
to wait for that perfect day for reattaching a broken taut band.
A meter that is sluggish, sounds like the pivots (if pivot and not the
modern taut band movement) are screwed in a little tight, or has had
excess current to expand the wire and charred insulation in the moving
coil. Otherwise it should never have gathered dirt (magnetic dirt is the
worst) to make it sluggish.
On the other hand a sensitive meter with a low value shunt will always
be sluggish because as the pointer moves it creates a back EMF just like
a motor (as it IS a motor) that when driven into a very low value shunt
will cause the meter to be sluggish. If this is a switchable multimeter,
it should not be very sluggish on plate voltage, but could be on plate
current. If its circuit that makes it sluggish, there is little that can
be done except to increase the resistance of the shunt, then add
resistance in series with the meter to bring the combination back into
calibration. That comes at the cost of increased power dissipation in
the meter shunt and poorer power supply regulation because of that added
shunt resistance (possibly not very significant).
I've opened meters and I've fixed one or two out per dozen attempted.
Doing anything significant requires the right touch on the right day,
else the meter gets trashed faster than I can say "oops." And that
applies to the meter repairer's I've known and used.
73, Jerry, K0CQ
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Entire content copyright Dr. Gerald N. Johnson. Reproduction by
permission only.
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