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Difficulty: MediumLaptop Power Systems and Battery Management

A technician is troubleshooting a corporate laptop that turns on and operates normally while connected to its AC power adapter, but the battery status icon reads 'Plugged in, not charging.' When inspecting the UEFI/BIOS system statistics screen, the AC Adapter Type is reported as 'Unknown' despite using the original OEM charger. Which of the following is the most likely cause of this issue?

  1. A bent or damaged center signal pin inside the DC power connector pinoutAnswer
  2. B
    The Lithium-ion battery requires a full deep discharge cycle to recalibrate its internal fuel gauge
  3. C
    The laptop operating system is missing DisplayPort Alt Mode drivers for the power port
  4. D
    The motherboard failed its initial Power-On Self-Test (POST) system memory check

Answer

A bent or damaged center signal pin inside the DC power connector pinout prevents charger identification and disables battery charging.
The correct option correctly identifies that OEM laptop power adapters utilize a center ID/sense pin to transmit power rating data to the laptop's embedded power management controller. If this pin is bent, broken, or disconnected, the system BIOS reports the adapter as 'Unknown' and safely disables battery charging while allowing basic operation.

Step-by-Step Solution

1
Analyze the reported symptom and BIOS observation.
The laptop runs on AC power, but the BIOS identifies the AC adapter wattage as 'Unknown' and refuses to charge the battery.
OEM laptop power supplies use a dedicated sense/signal line (often a thin center pin in the barrel plug or ID pin) to communicate power ratings to the laptop power management controller.
2
Evaluate hardware power safety mechanisms.
When charger identification fails, the system defaults to a protective state where it allows basic system operation on AC power but disables charging to prevent thermal or electrical overload.
Connecting an unverified or underpowered charger could cause excessive heat or hardware damage if fast charging were enabled.
3
Identify the root cause.
Physical damage or a bent center signal pin on the connector interrupts charger identification data signals.
Inspecting and replacing the damaged AC power adapter or DC-in jack resolves the unknown adapter error.

Key Concept

Laptop DC Power Signal Pin Identification and Charging Safety Features
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Topics

Laptop Power Systems and Battery Management

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