Common maintenance methods for inverters - Solutions - Huaqiang Electronic Network

Photocoupler

1. Ten General Maintenance Methods: ● Observe: Look at the fault symptoms, identify the root cause, and inspect the entire board and machine. ● Measure: Use a multimeter to check components, solder joints, and tin points. ● Test: Measure waveforms and use test boards for verification. ● Listen: Pay attention to sounds from relays, inductors, and contactors — no unusual noise should be heard. ● Touch: Feel ICs, MOSFETs, and transformers for overheating. ● Disconnect: Cut signal connections by removing printed circuits or component pins. ● Short: Temporarily short a control signal to another point for testing. ● Press: A faulty component may temporarily fix itself when pressed, often due to poor soldering or loose connections. ● Tap: This method is effective for checking relay movement or internal issues. ● Discharge: Before removing resistors or capacitors, make sure to discharge them first. 2. Common Causes of Failure: ● Faulty Repaired Boards: Issues like cold soldering, bridging, incorrect mounting, misassembly, damage, or missing parts. ● Units Sent for Repair: Problems such as knocked-out components, improper plug-in, wrong wiring, or damaged devices. ● Spare Board: Damaged components on the spare board. ● Spare Parts: Damaged spare parts used during repair. 3. Maintenance Experience Tips: ● As the saying goes: "A good memory is not as good as a pen." Knowledge is valuable, but experience is even more so. If you have solid skills, both will help. ● Experience is useful, but it can't solve every problem. The future brings new situations that may not match past experiences. ● While experience can guide you when you're stuck, it shouldn’t be relied on entirely. Always verify with tests and logic. ● When a system fails, start by testing the control board using a simple tooling setup. Alternatively, replace the board or module to isolate the issue. 4. Common Inverter Maintenance Experience (Emerson Series Example): 1. Pre-Maintenance Notes: Below are some abbreviations used: - "Red" refers to the red probe of the multimeter. - "Black" is the black probe. - "Two" means the diode mode. - "Ohm" refers to the resistance mode. - All units are in volts. - "+" stands for the positive busbar. - "-" stands for the negative busbar. - LN or RST refers to the input power. - UVW refers to the output power. 2. Important Steps Before Powering On: (Step One) Check the IPM quality: Use the diode mode. Connect the red probe to "-", and the black probe to RSTUVW. The reading should be around 0.5 V. Then reverse the probes: connect the black to "+", and the red to RSTUVW — again, the value should be about 0.5 V. If not, the IPM is likely damaged. If it reads 0.5 V, it only indicates that the freewheeling diode inside the IPM is working. Next, test the optocoupler connected to the IPM: set the meter to diode mode. Connect the red probe to pin 5 and the black to pin 6 — the reading should be around 0.55 V. Then connect the red to pin 7 and black to pin 8 — the reading should be approximately 0.77 V. This confirms the optocoupler and IPM are functioning. If the optocoupler is faulty, the IPM is likely damaged too. Also, if the IPM is broken, related resistors and diodes may also be bad. (Step Two) Check the switching power supply MOSFET: Look for burnt gate resistors or changes in measured resistance values, which may indicate a faulty gate resistor, MOSFET, or associated chip (e.g., 2844). If after replacement, there's no display or the fan runs too fast (high voltage), the four-pin optocoupler (like PC9) might be damaged. If steps one and two pass but the inverter still has no display, the switching power supply diode could be faulty. To check the diode: connect the red probe to the anode and the black to the cathode. A good diode should read between 0.4–0.5 V (for one type) or 0.2–0.3 V (for another). If the diode shows 0.14 V in both directions, it’s likely damaged. If the switching power supply is faulty, the fan may not turn on, the voltage may be low, and the D3 diode may show a forward/reverse voltage of 0.14 V, indicating a fault.