As a general principle, when the intermediate frequency power supply fails, the whole system shall be comprehensively checked under the condition of power failure, which includes the following aspects:

（1） Power supply: use a multimeter to check whether there is power behind the main circuit switch (contactor) and control fuse, which will eliminate the possibility of open circuit of these elements.

（2） Rectifier: the rectifier adopts three-phase full control bridge rectifier circuit, which includes six fast fuses, six thyristors, six pulse transformers and one continuous current diode. There is a red indicator on the fast fuse. Normally, the indicator shrinks inside the shell. When the fast fuse is burnt out, it will pop up. Some fast fuse indicators are relatively tight. When the fast fuse is burnt out, it will be stuck inside. Therefore, for the sake of reliability, a multimeter can be used to test whether it is burnt out.

The simple way to measure the thyristor is to measure its cathode anode and gate cathode resistance with the multimeter resistance block (200 Ω block). During the measurement, the thyristor does not need to be taken down. Under normal circumstances, the resistance between anode and cathode should be infinite, and the resistance between gate and cathode should be between 10-50 Ω. Too large or too small indicates that the gate of this thyristor is invalid, and it will not be triggered.

The secondary side of the pulse transformer is connected to the thyristor, the primary side is connected to the main control board, and the primary side resistance is about 50 Ω measured with a multimeter. In general, the continuous current diode is not easy to fail. When checking, use the multimeter diode to block the two ends. In the forward direction, the multimeter shows that the junction voltage drop is about 500mv, and the reverse direction is blocked.

（3） Inverter: the inverter includes four fast thyristors and four pulse transformers, which can be checked according to the above methods.

（4） Transformer: each winding of each transformer should be on. Generally, the primary side resistance is about tens of ohms, and the secondary pole resistance is several ohms. Xi'an intermediate frequency power supply should note that the primary side of the intermediate frequency voltage transformer is parallel to the load, so its resistance value is zero.

（5） Capacitor: the electric heating capacitor in parallel with the load may be broken down. Generally, the capacitor is installed on the capacitor rack in groups. During the inspection, the group of the broken down capacitor shall be determined first. Disconnect the connection point between the bus bar of each group of capacitors and the main bus bar, and measure the resistance between the two bus bars of each group of capacitors, which should be infinite under normal conditions. After confirming the broken group, disconnect the soft copper skin from each electric heating capacitor to the bus bar, and check one by one to find the broken capacitor. Each electric heating capacitor is composed of four cores, the shell is one pole, and the other pole is respectively led to the end cover through four insulators. Generally, only one core will be broken down, and the lead on this insulator will be disconnected. This capacitor can continue to be used, and its capacity is 3 / 4 of the original. Another fault of the capacitor is oil leakage, which generally does not affect the use, but attention should be paid to fire prevention.

The angle steel for installing the capacitor and the capacitor frame are insulated. If the insulation breakdown will make the main circuit grounded, the insulation condition of this part can be judged by measuring the resistance between the capacitor shell lead and the capacitor frame.

（6） Water cooling cable: the function of water-cooling cable is to connect intermediate frequency power supply and induction coil. It is made of each Φ 0.6 – Ф 0.8 purple copper wire. For 500 kg furnaces, the cable cross-sectional area is 480 mm2, for 250 kg furnaces, the cable cross-sectional area is 300-400 mm2. The outer rubber tube of the water-cooled cable is a pressure rubber tube with a pressure of 5kg, which is connected with cooling water. It is a part of the load circuit. When it works, it is subject to tension and torsion, and turns with the furnace body, so it is easy to break at the flexible connection after a long time. In the process of breaking water-cooled cables, most of them are cut off first, and then a small part of them will be burnt out quickly when they are running at high power. At this time, if the over-voltage protection is not reliable, the thyristor will be burnt out. After the water-cooled cable is disconnected, the if power supply cannot be started. If the reason is not found out and the startup is repeated, it is likely to burn out the intermediate frequency voltage transformer. In case of failure, use an oscilloscope to clamp the oscilloscope probe at both ends of the load, and observe whether there is attenuation waveform when pressing the start button. When the cable core is broken, disconnect the water-cooled cable from the output copper bar of the electric heating capacitor, and measure the resistance value of the cable with the multimeter resistance block (200 Ω block). Normally, the resistance value is zero, and when the cable is disconnected, it is infinite. When measuring with a multimeter, turn the furnace body to the dumping position to make the water-cooled cable fall off, so that the broken part is completely separated, so as to correctly judge whether the core is broken.