(1) What is the problem with one of the four rectifier diodes.
(2) There is carbon powder between the rotor and the motor commutator, or the motor carbon brush itself is not good. Adhering to targeted maintenance standards, we first accurately measured the variable resistor, and the resistance value changed periodically with adjustment, confirming that the resistor was good. Even after accurately measuring the thyristor, no problems were found because the diode is a high current metal sealed tube. One end is screwed tightly to the circuit board, and the other end is wrapped and welded to the circuit board. When removed from the circuit board, we found that the positive and negative terminals were loose. We then measured accurately while shaking to confirm that the diode was intermittent.
(3) There are also many situations that occur with thyristors, such as through short-circuit faults, routing faults, inability to open, or poor internal contacts.
(4) Variable resistor, the vertical centrifugal fan is installed on the operation panel due to the variable resistor, and the application frequency is particularly high. Over time, the situation of loosening is very common.