Repairing D'Arsonval Meters
Calculating Shunt Values and common metering circuits
The most common failures in old D'Arsonval meters that have not been wet, subjected to grossly excessive current, or otherwise physically damaged relate to bad electrical connections.
Remember when you dismantle the meter, work in a clean lint-free location. No dog or cat hair, and especially no steel or iron shavings! The following DX60 meter measured open and did not deflect.
There are two electrical paths. The rear regulator has a wire directly soldered to it, and that regulator is soldered to the hairspring. The hairspring makes a connection to the motor coil, which is also soldered. There is not much chance of a bad connection here.
The locations for bad connections are pressure connection points. They would be the two meter studs and the small screw. Securely tighten these three points.
The remaining slotted head screw can be checked for snugness. Unless it falls out, it is not a problem.
Do NOT adjust or move anything else! Do not get trash in the meter movement.
After snugging these three points, this meter started to work. It measured about 65 ohms.
In the front area, the front regulator is solidly soldered to the hairspring. The hairspring makes the electrical connection to the motor coil.
I dropped some liquid WD40 on the pressure contact area with a wooden toothpick. After wetting the area of the nut, I moved the regulator arm back and forth a few dozen times. I reset it to the original position so it would line up with the plastic adjustment post stub in the meter front.
After cleaning this contact, this meter read 50.3 ohms!
Do not adjust anything except position of the regulator arm.
I thoroughly cleaned the inside of the case by blowing it out with air. I wiped it down with a clean tack cloth.
I put a very thin layer of high viscosity pure clear silicon grease near the back bottom, and also around the meter terminal screw holes AFTER completely cleaning the case. This will help trap any debris or dirt I missed, or anything that gets knocked loose during assembly.
Notice all the small white dots. This is trash from the deteriorated meter seals where the two large connection studs go through the plastic. A light coating of thick 100% pure silicon grease on the holes will serve as a good seal, and trap any loose particles I could not scrape away.
Scotch tape works to pick up debris.
Only snug the rear outside nuts. The plastic won't take much torque. This meter case was already cracked before I opened it.
I sealed the crack on the OUTSIDE only with super-glue applied with a toothpick.