Fault route · Feeder does not stop
NBC / CO2-MIG wire feeds continuously
Use this page when the feeder motor keeps running after the torch switch is released, runs as soon as the machine powers on, or ignores 2T/4T and burn-back settings. The key is to separate stuck command logic from shorted motor-drive hardware.
Two different faults look similar
Command path stuck ON
Torch input, 2T/4T latch, burn-back timing, crater/slow-feed logic or relay command may remain active.
Power path shorted ON
Motor transistor/MOSFET, relay contact, flyback/snubber damage or solder bridge may power the motor even without command.
Stop-sequence checks
| Check | Expected behavior | Fault clue |
|---|---|---|
| Remove torch trigger input | Motor should stop if command is only from gun switch. | If motor stops, suspect torch switch, cable or trigger line short. |
| Switch 2T / 4T mode | Motor behavior should change according to mode. | No change suggests latch/mode logic or stuck output stage. |
| Turn speed pot to minimum | Motor speed should reduce or stop depending on design. | No duty change suggests motor output short or PWM control failure. |
| Check burn-back timing | Short post-trigger motor activity may be normal burn-back behavior. | Long or infinite run indicates timing capacitor/path or command latch fault. |
| Measure motor output with command removed | Output should fall near zero. | Voltage remains high: check relay contact, MOSFET/transistor short or board contamination. |
Likely parts by symptom
Runs at power-on
Check motor switch transistor/MOSFET short, relay contact welding, board contamination and connector miswire.
Stops late
Check burn-back timing circuit, timing capacitors, potentiometer and 2T/4T latch signal.
Runs after trigger release
Check torch switch line, 4T latch, crater control and command line from main control board.
Repair priority
First decide whether the board is still commanding feed or whether the motor power device is shorted. Replacing the PWM IC will not fix a welded relay contact, and replacing a motor will not fix a stuck 4T latch.