Analog Instrument repair

[lukin1977]

I have a faulty analog instrument. The needle does not move. I checked the signal coming to the instrument and signal is Ok
I feed the instrument with a 9V battery and nothing so I open up the instrument
Found out that there is a tiny coil that is damaged (the little black coil in the pictures)

How can I repair this?
What is the function of this coil? Is it part of an internal LR filter?

Any comments will be appreciated

 

[ScottyUK]

Is this an AC or DC instrument? That would give a clue to the purpose of the coil.

 

[lukin1977]

Is a DC Instrument
The input signal comes from a Tachometer of a DC motor

 

[OperaHouse]

Those are generally a custom wire wound resistor. What makes you think it is bad? Resistance is generally high. If that is damaged, the meter coil is likely shot. If it Might be time to just stick a digital readout in that case.

 

[flexoprinting]

Hi Luukin

Possibly you could use the calipers in background of your picture measure the wire count the turns on coils and rewind them. Just a thought.

Chuck

 

[waross]

The overwhelming majority of those analog instruments were milli-ammeters with d'Arsonville movements.
Use a limiting resistor to pass 5 or 10 ma through the meter movement. Change resistors to find out the current required to produce full scale deflection.
If the meter will not respond, buy a 0-50 ma milliammeter to replace it.
Or, if the wound resistor is open, calculate the resistance required to produce full scale deflection with your signal and replace the resistor.
If you don't need high accuracy, you don't need a wire wound resistor.
You may have to replace both the meter and the resistor.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[lukin1977]

OperaHouse: The wire of the wire resistor is broken (shorted). The picture cant tell but it is

I am trying to rewound the coil: same wire size, same turns and see what happens
I will come back with results

 

[lukin1977]

The instrument is back in service
The coil was rewound
Thanks to all!