How to repair the pulse transformer on the induction melting furnace?

Whether it is a rectifier pulse (6 small pulse transformers on the control board) or an inverter pulse (installed in another place, depending on the pulse pulse transformer used by the tungku peleburan induksi manufacturer, there is a single transformer or two transformers together. For small circuit boards, there are 4 transformers on one circuit board). But there is a red or green light-emitting diode on the side of each transformer. When the pulse is normal, these diodes will emit light. Of course, sometimes the light-emitting diode itself is broken.

So is it certain that the light-emitting diodes are on to indicate that the pulse is normal? the answer is negative. The output part of some pulse circuits is equipped with two diodes, one is similar to half-wave rectification to provide forward trigger voltage to the thyristor, and the other is reversed and connected to the output terminal to limit excessive voltage output. Assuming that the previous diode used for rectification is broken (open circuit), the voltage-limiting diode becomes rectified, and the light-emitting diode still emits light when it has a forward voltage. Therefore, the light-emitting diode can not accurately determine whether the pulse transformer is damaged.

In the case of checking the integrity of other components (mainly thyristors), the way to judge whether the rectifier pulse is good or not: remove the common wire of the three inverter pulse wires on the control board. For the MPU-2 type control board, Turn the small switch No. 1 on the board to the opposite end (turn off the sweep circuit), then turn on the intermediate frequency power supply according to the program, turn the power potentiometer on the door panel to the maximum, and observe whether the DC voltage is 400～500V? If it is, it means that the rectifier circuit including the rectifier pulse is basically normal; if the DC voltage is abnormal or very low, remove the gates of the rectifier thyristor one by one and observe. Remember, if the thyristor with normal pulse is removed, The voltage will be lower. If the thyristor that is damaged by the pulse is removed, there is no response on the meter, as if the wire is not removed, it means that there is a problem with the corresponding pulse. Remove the pulse board, if there are two diodes at the output end of the pulse board, solder one end of the next diode, then measure with the resistance of a universal meter, and replace the broken one.