Preliminary Appearance and Functional Inspection
1. Appearance Inspection: Check the welding machine casing and terminals for obvious signs of burning, deformation, or oxidation. Also check for any abnormalities around key components on the circuit board (such as the rectifier bridge and capacitors).
2. Power-on Test: After connecting the power, observe whether the indicator lights illuminate and whether the fan runs. If there is no response, the problem may be with the power cord, fuse, or socket.
3. Open-circuit Voltage Measurement: Set the multimeter to the DC voltage range and measure the open-circuit voltage at the welding machine's output. The normal value should exceed 60V (60-80V for AC welding machines, and over 50V for DC welding machines). If the voltage is too low or there is no output, there may be a fault.
Key Component Inspection (Power Off Required)
1. Rectifier Bridge Inspection: Use the diode setting on a multimeter to measure the voltage drop between the positive and negative terminals of the rectifier bridge and the AC input pins (normally about 0.5V). If the measured value is 0, it indicates a short circuit in the rectifier bridge.
2. Inverter Diode Testing: Using the diode setting, measure the voltage drop between each pin of the inverter diode (normally approximately 0.5V). If there is no voltage drop or abnormal resistance between any pair of pins, the diode may be damaged.
3. Output Diode Testing: Measure the output terminals of the welding machine. If a short circuit is present, the output diode may be faulty.
Function Verification and Abnormal Phenomena
1. Listen for sound: A normal welding machine produces a uniform "humming" sound after power-on. If a popping sound or complete silence occurs, be alert to potential internal component problems.
2. Trial Soldering: Attempt arc welding. If the arc is unstable, fluctuates in size, or frequently breaks, it may indicate poor contact in the welding torch switch or aging of the output cable.
Safety Precautions
1. Always disconnect the power before testing to avoid the risk of electric shock.
2. If bulging, cracked, or burnt components are found, it is recommended to contact a professional repair technician.
