XO 1.75 A2 ECOs

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These are recommended engineering change orders (ECOs) to the A2 prototype of the XO-1.75 laptop. This is NOT a list of changes from A2 to A3, that is located elsewhere.

Contents

SD power

These correct a mistake in Embedded Controller pin assignments for the SD power control signals. It has been done to all boards.

  • Depopulate R335 and R345 (next to the EC).
  • Remove Q16, and short pins 2 and 3 (marked I and O).
  • Remove Q21, and short pins 2 and 3 (marked I and O).

VMEM stability

This corrects an undercompensation of the +1.5V memory power supply, and also delays the turn-on of the memory termination power supply. It has been done to all boards.

  • Change PR49 to 22K.
  • Change PR52 to 47K.
  • Populate PC37 with 0.1 uF.

eMMC

This adds a needed pullup to the eMMC CMD signal.

Done to all boards.

  • Populate R95 with a resistor between 4.7K and 10K.

Internal SD Selection

This makes OFW automatically use the internal SD (instead of eMMC) if a card is present in the internal slot.

  • Wire the non-grounded pin of R342 (located on the "top" side underneath the SOC) closest to the WLAN slot to pin 10 of CN21 (the internal SD slot) or TP117.

DCON Soft start

This fixes a supply voltage glitch caused by turning on the LCD 1.8V power (the glitch is caused by the DCON, not the LCD).

Done to all boards.

  • Cut the trace going to the gate of PQ22.
  • Insert a 47K resistor in the trace
  • Tie a 0.1uF capacitor between the gate of PQ22 and ground.
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