Laptop DC Power Input Stage: Failed reverse-polarity protection | Auckland
Pattern to record: The adapter is recognised mechanically but no protected voltage appears beyond the input stage.
Identify the input design
This guide concerns a laptop powered through a round DC jack. The adapter label and the laptop model determine the required voltage, polarity and rating; a plug that fits is insufficient evidence of compatibility. One possible explanation is that the input MOSFET or protection stage no longer passes valid adapter power.
Stop before further damage
Stop using any connector that sparks, smells hot or has visibly melted plastic. Guessing at MOSFET orientation can expose the board to full adapter current.
Workshop checks
- Compare adapter voltage at rest and under load, inspect the connector mechanically and trace protected input power with the battery isolated.
- Compare gate, source and drain conditions using the correct circuit reference.
Repair and power verification
If the checks support this cause, replace the failed protection device after confirming no secondary short remains. Verification should cover cold start, charging under load, connector temperature, battery transition and repeated plug cycles.
For an assessment of your barrel-charger laptop, contact AEPC in Burswood or call 027 908 8880. Provide the model and the conditions that reproduce this problem. Workshop visits are by appointment.