Repair Case
Dual-Voltage Board Not Boosting
Use this page when a 220V/380V inverter welder powers on but the input switching or boost stage does not produce the expected DC bus level.
Main checks
| Check | Expected | If abnormal |
|---|---|---|
| Input selection/detection | Board detects 220V or 380V correctly | Detection resistor, comparator or optocoupler fault |
| Relay coil supply | Relay receives rated coil voltage when commanded | Driver transistor, diode or auxiliary supply fault |
| Relay contacts | Contacts close with low resistance | Pitted contact or failed relay |
| DC bus | Bus rises to expected level for the selected mode | Bridge, capacitor, boost/doubler path or relay fault |
Repair notes
- Use a current limiter for first power-up after input-stage repair.
- Check bus capacitors and discharge resistors before testing live voltage.
- Do not force the relay without understanding whether the board is in 220V or 380V mode.