Hickok 539B with a broken meter

[cwr56]

Hi, I have an interesting problem. I have a Hickok 539B, with a broken Micromho meter. Actually, the D'Arsonval movement itself seems to work properly with current applied, but the needle assembly and top hairspring has come unglued from the moving coil.
The coil has it's pivot points inside the coil, so it pivots on the magnet, unlike most other D'Arsonval movements I've seen.

So basically, the coil rotates as it should, but the needle is just sitting there on top of it, with the glue that holds it together broken.

His anyone had any luck repairing these? I figured just take a toothpick and dab a tiny dot of epoxy to the top of the coil, line up the needle again on top, and let it set.
Sound like it would work?

-John

[Mikeinkcmo]

I'm not doubting what you say, but how are both sides of the coil connected to the current source? I thought that one side was through the front coil spring and the other through the rear spring.

Mike
_________________
Mike Harrison, KE0ZU.
Out in the country, not far from Jessy James' farm.

[W. Arnold]

Hi John,
I repaired meters commercially for over 13 years many moons
ago, 50s & 60s.
Hickok's have a weakness & you found it, the glue was crap.
Your fix is exactly what I have done many times.
Don't use a fast setting glue or you could have trouble.
I block moving coil from underneath with 4 round tooth
picks so it is exactly centered left & right.
There is a hole in top bar, push a shaved tooth pick thru & anchor
the top plate with the pointer at exactly center scale.
You can hold pointer there with a piece of notched paper folded
& with one fold slid under scale plate.
Be careful to have plate centered left & right & front to back of coil.
Then put small dab of glue on both sides of plate using a long fine needle
with just a little at a time on very tip.
Sometimes I put just a little on & let it dry so I can then remove
all tooth picks & apply a little more without them in way.
If spring is in way, carefully push it up slightly where it is soldered
to zero corrector.
When all done spring can be carefully readjusted.
When all is dry, you have another thing to do, that is to poise the meter.
If the meter is never set up vertically you only need to
get close to balance, but if it is at any angle, you need to poise carefully.
Some poise weights twist to adjust & some only push.
Do not twist or push so hard that you destroy your glue job.
If the balance is not too far off, sometimes I just put some meltable
material on end of cross pieces.
You could use some wax. Do both side & end poise, one at a time.
Your last job is to very carefully clean all junk out of air gap using
a magnetic sewing needle stuck in a small wooden dowel.
Do not put needle near coil as it can break the coil wire.
If any of this is not clear email me w_arnold@att.net.
Good luck
Wm.

[cwr56]

Well, I just got done, but I did it on the zero mark of the meter, not the center. I carefully applied the 2 hour epoxy to the top of the coil, then very carefully adjusted the needle on top of the coil (very good eyesight), so it looked perfectly even, and now I'm waiting for the glue to set.

BTW, to answer your question why it still worked, the glue gave way, but the tiny wire was still intact.

We'll soon see how well it worked.

-John

[cwr56]

Well, the repair seems to hold well. Only problem, is the outer end of the upper hairspring seems very weak, right where it's soldered on to the adjusting lever, it seems to have flexed quite a bit there when the needle was just floating around. Anyone have any suggestions?

Is anybody able to replace a hairspring?