Reparing my Soldering Iron

After being fed up of buying new soldering iron because they easily get damaged(I had just bought a new one which stopped working only after a week) and I have three of them and because soldering iron is essential tool for building electronics circuit, I decided to try to repair these at home. Because suppose I was to work in a place where there is no where to buy and get immediately a soldering iron then such repair knowledge can be very helpful and it is one of the tools that are easily destroyed.There are other reasons as well to learn how this soldering iron works because the same concept is applied in for example, cooking heater, water heater, diy incubator, Woodburning (pyrography) pen,Foam cutter, Mini heat sealer,DIY wax or plastic melter etc.

Below are some pictures I have taken of my malfunctioning soldering iron.

There are only few components, the heater made up of the Nichrome coil(Nichrome is an alloy of nickel and chromium (80% Ni, 20% Cr)) assembly which has two terminals to which the AC main power supply are connected. A neon bulb with 150kohm resistor is connected across the coil terminals. Hence the across the parallel circuit of the cold and the neon bulb +resistor circuit. The AC main voltage of 230 VAC is applied directly to the coil. A single coil is used to make couple of layers wound around a metallic cylinder and then terminating the ends of the wire with another metallic wires to make the ends of two terminals. By applying the ac main voltage the coil layers heats up due to the resistive heating(Joules).

Circuit Diagram of Soldering Iron

I made a simple circuit diagram showing the main soldering parts. The AC main power supply to the two terminals of the nichrome wire. The nichrome wire made actually of layers is shown as a resistor with resistances of 50 ohms to 500 ohms.

Troubleshooting Soldering Iron

My guess was that the nichrome coil broke due to overheating and sudden cooling because where I live the ac main is over 230 VAC sometimes and the ac main suddenly gets cut off. This could explains the reason for all of the 3 soldering irons to malfunction(not heating up). So first I checked the continuity between the two terminals of the coil, and since it is a single coil distributed in layers, there should be a beep. But I did not get any continuity beep. I measured the resistance of the nichrome wire coil and I got over 30Mohm which is too much and can be assumed open circuit. This means the coil is broken somewhere.

So next, I checked the outer most layer nichrome coil under a magnifying glass and saw a break in one of the ring. Below is picture of the broken nichrome wire of my soldering iron.

The neon bulb with 150kohm resistor in series used with the soldering iron as power indicator is shown below.

So I have to unwind the coil and rewind without any break in connection.

Reparing my Soldering Iron

Circuit Diagram of Soldering Iron

Troubleshooting Soldering Iron

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