> Sounds a bit as if one or both hairspings have become
> unconnected. It's got to be worth opening it up to have a
> look, but whether or not it's repairable without special
> tools and equipment is another matter. For opening it up
> (this is probably teaching grandmother to suck eggs
> but........)
If a hairspring is broken the meter will stick (if it hangs
up on something), not read at all (the current path is
through the springs in conventional movements), or it will
be far too sensitive (in a moving magnet movement). It also
won't zero. The hairsprings set the zero position. One is
generally adjustable outside with the zero regulator, the
other is set by the assembler to make the external regulator
fall in range.
Since he reports normal meter operation except for there
bounce it has to be a dampening problem. When we made panel
meters back in the 70's and 80's we used a tiny amount of
controlled viscosity silicone on the meter movement pivots.
The silicone did the required dampening.
Other things that control "bounce" are the mass of the
moving parts and the torque of the meter. Some meters have
very sensitive (low power) movements with almost no spring
or motor force and they move slowly, and some have very high
torque and moving part weight and the friction is such a
small part of losses the pointers will bounce. We know none
of this changed.
It sounds to me like his meter jewels have dried out and it
is simply a bouncy meter. I had one do that in a receiver.
If a person is careful and has a clean area to work he can
loosen the lock nuts (or dissolve any thread locking) and
remove the bearing screws. A small wetting of silicone oil
will dampen the movement, but the problem is not breaking
anything in the process.
It can be fixed. It can also be broken.
73 Tom
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|