1. After turning on the power, the control panel displays normally and the cooling fan works normally. When the start button is pressed, the intermediate relay works and the centrifuge does not work. According to the analysis of the fault phenomenon, the power supply and control parts should be normal, and the fault should be in the circuit from the control board to the motor, the carbon brush, and the motor. Open the centrifuge and use a multimeter to measure the continuity of the circuit from the control board to the carbon brush. Then measure that the carbon brush is not conducting to the motor rotor. Carefully observe the poor contact between the carbon brush and the motor rotor. After removing the carbon brush, it was found that it was caused by too long or too short usage time. Replace the carbon brush with a new one and troubleshoot the issue. This type of malfunction is a common problem with centrifuges, and it is necessary to regularly replace the carbon brush to avoid the above malfunctions.

2. After turning on the power, the control panel displays normally and the cooling fan works normally. When the start button is pressed, the intermediate relay does not work and the centrifuge does not work. According to the analysis of the fault phenomenon, the power supply should be normal, and the fault should be in the control board and the circuit to the motor, carbon brush, and motor. Turn on the centrifuge and use a multimeter to measure the continuity of the circuit from the control board to the carbon brush. Then measure the continuity of the circuit from the carbon brush to the motor rotor, and confirm that the motor coil is normal. After turning on the machine, use a multimeter to measure that there is no voltage output in the wire from the control board to the motor. It can be determined that the fault should be on the control board. The intermediate relay is not working, and the fault should be on the control circuit that controls the intermediate relay. After troubleshooting one by one, it was found that the C9013 transistor on the control board had broken down, and the new C9013 transistor was damaged. The fault was resolved.

3. After turning on the power, the control panel displays normally. When the start button is pressed, the centrifuge works normally. But when the stop switch is pressed, the centrifuge does not respond and cannot stop working. According to the analysis of the fault phenomenon, the fault should be in the stop control part of the control circuit, which includes the stop switch, power control board, and timer control board. Turn on the centrifuge and use a multimeter to check the stop switch, which is normal; After powering on, the signal output from the power control board to the timer control board is AC 16V, which is normal. The fault should be on the timer control board. The timer control board cannot execute the stop task when it receives a stop signal. One by one, it was found that the C9013 transistor and capacitor with a model of 16V and 470 μ F on the timer control board had broken down, and the new transistor and capacitor were even worse. The fault was resolved.

4. After turning on the power, the control panel displays normally. When the start button is pressed, the centrifuge works normally. But when the stop switch is pressed, the centrifuge cannot stop working immediately, but rotates for a long time before slowly stopping. According to the analysis of the fault phenomenon, the fault should be in the stop brake control part of the control circuit, which includes a WJ176-12V intermediate relay, a brake resistor R: 20-30 Ω, a KBPC50A10M silicon stack, and wires. Turn on the centrifuge and use a multimeter to measure the brake resistance, intermediate relay, and wires, all of which are normal. After starting up, press the stop button and use a multimeter to measure the four corners of the silicon stack. There is an AC 12V input but no DC 12V output, indicating that the silicon stack is faulty. Replace it with a new one and troubleshoot the issue.