Fault
Welder connected to 380V by mistake
Wrong-voltage damage path: input fuse, varistor, rectifier, capacitors and auxiliary power.
Damage pattern
When a welder is connected to the wrong high input voltage, the damage usually starts at the input protection and energy-storage path. The fault can then spread into the auxiliary supply and control board. A machine that only blows the fuse may still have hidden rectifier, capacitor or varistor damage.
Inspection sequence
Disconnect and discharge
↓
Inspect fuse / breaker
↓
Inspect MOV / NTC / input traces
↓
Test bridge rectifier
↓
Inspect bulk capacitors
↓
Check auxiliary PWM supply
↓
Check control-board rails
↓
Power up with current limiting
Common damaged parts
- Input fuse or breaker.
- MOV/varistor cracked or shorted.
- NTC limiter damaged.
- Bridge rectifier shorted.
- Bulk electrolytic capacitors bulged or vented.
- Auxiliary supply startup resistor or PWM controller damaged.
Do not simply replace the fuse
Replacing the fuse without checking the input bridge, capacitors and auxiliary power stage can cause a second failure and may destroy more expensive parts.