Electronic – MS Surface power supply

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I have a faulty Microsoft Surface power supply and I found a circuit diagram for it that I could use some help figuring it.

Circuit diagram. Rightmost box is the Surface device itself, central box is the connector (pictured in next image), and the remaining circuit on the left is the power supply. Red, blue, and silver are colours of the wires inside the power supply's insulation.
Connector of power supply that plugs into the Surface device

Specifications:

  • The LED is supposed to be on only when the Surface's Power On
    Controller tells the connector it is charging (with the Surface receiving a 12V pulse every half second)
  • At all other times LED is supposed to be off
  • If however, there is any sort of problem with the power supply, the
    LED will blink
  • Blinking means the pulse generator is causing the LED to blink, which
    is somehow prevented when things are functioning properly

Can someone figure out what prevents the LED from blinking during normal operation, and more importantly, what flaw might cause it to blink?

Best Answer

During normal operation: When the MOSFET in the Connector box switches on (pulls the Blue line low) it prevents the pulses from the "Pulse Gen" from getting to the main power MOSFET (the left side MOSFET), those pulses are effectively shorted out, the main power MOSFET is full on, and the LED pair is also full on, (not blinking).

For a flaw that might cause it to blink: If the MOSFET in the Connector box went bad, or the Power on Controller went bad, or the resistor or the 3.3v (above that) went bad. In those cases the LED might be blinking instead of full on. Possibly even a loose 12v connection (from the battery or connection on the left side) could make it blink. To be thorough I suppose you could also include the possibility of loose (dirty or worn out) pins in the connector box making it blink too.

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