Welding is a condition where only a small amount of tin is soldered at the solder joint, resulting in poor contact and occasional on and off. False welding means that it seems to be welded on the surface, but in fact it is not. Sometimes the lead can be pulled out from the solder joint by pulling it out by hand. These two situations will bring great difficulties to the debugging and maintenance of electronic production. Both of these situations can only be avoided with extensive, careful welding practice. When welding circuit boards, be sure to control the time. If it is too long, the circuit board will be burned or the copper foil will fall off. When removing components from the circuit board, you can stick the soldering iron tip on the solder joint and pull out the component after the tin on the solder joint melts. The temperature of the soldering iron has a certain relationship with the volume, shape, length, etc. of the soldering iron tip. When the volume of the soldering iron tip is relatively large, the holding time will be longer. In addition, in order to adapt to the requirements of different welding objects, the shape of the soldering iron tip is different. Common ones include tapered, chisel-shaped, rounded bevel, etc.

Use the ohm setting of a multimeter to measure whether there is an open or short circuit at both ends of the plug, and then use the Rx1000 or Rx10000 setting to measure the resistance between the plug and the shell. If the pointer does not move or the resistance is greater than 2-3MΩ, it can be used safely without leakage. The soldering iron core of the internal heating electric soldering iron is made of relatively thin nickel-chromium resistance wire wound on a porcelain tube. Its resistance is about 2.5kΩ (20W). The temperature of the soldering iron can generally reach about 350OC. The internal heating soldering iron has the characteristics of fast heating, light weight, low power consumption, small size and high thermal efficiency, so it has been widely used. After the soldering iron is connected to the power supply, if it is not hot or not too hot, check whether the power supply voltage is lower than AC210V (normal voltage should be AC220V). Too low voltage may cause insufficient heat and difficulty in soldering. The soldering iron tip is oxidized or the fastening part between the root end of the soldering iron tip and the inner wall of the outer tube is oxidized. The reason why the neutral line is charged is that in a three-phase four-wire power supply system, the neutral line is grounded and has the same potential as the earth. If the neon bulb glows when tested with a voltage test pen, it indicates that the neutral line is charged (there is a potential difference between the neutral line and the earth). An open circuit in the neutral line, an increase in the grounding resistance of the neutral line, an open circuit in the ground down conductor, or a grounded phase line will all cause the neutral line to be electrified.