XO 1.75 A2 ECOs

From OLPC

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.

[edit] 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).

[edit] 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.

[edit] 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.

[edit] 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.

[edit] 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.