[Amps] Follow-up on Bouncy Meter

[Tom W8JI]

> 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