XO4 C1 ECOs

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These are recommended engineering change orders (ECOs) to the C1 prototype of the XO-4 laptop. This is NOT a list of changes from C1 to C2, that is located elsewhere.

External SD Power Switch

There is a problem with the external SD power switch which prevents it from supplying +1.8V to the card. This can be fixed by:

• Replace R416, R417, and R420 with zero ohm resistors.
• Remove R414. Wire a 220K resistor between Q54, pin 3, and +3.3V_NAND. One location where this is readily available is PR102 (either end, above the battery connector and PU10).
• Remove C498
• Change R415 to 220K
• Change C420 and C496 to 0.1 uF
• Replace Q50, which has been removed, with an AO3402.

All components mentioned except PR102 are located on the "bottom" side of the PCB next to the external SD slot.

Modify the Board ID

Modify the board ID to 4C2 to communicate the new SD Power Switch capabilities to software:

• Change R337 ("bottom" side, near the EC) to a 33K resistor

Shorter version

This one has slightly longer turn-on/turn-off times, but otherwise works fine and halves the soldering required. The board ID should also be modified.

• Replace R416 and R420 with zero ohm resistors (anything less than 50 ohms will do).
• Remove R414. Wire a 100K resistor between Q54, pin 3, and +3.3V_NAND. One location where this is readily available is PR102 (either end, above the battery connector and PU10).
• Remove C498
• Replace Q50, which has been removed, with an AO3402.

Testing

A quick test if the ECO was done correctly is to manually control the external SD power from OFW and measure the voltage. Boot into OFW. Then turn on +1.8V to the external SD card using:

ok d# 116 gpio-set
ok d# 115 gpio-set

Check the voltage at pin 4 of the external SD slot (count from the white dot, not the end pin!) It should be +1.8V.

Now try +3.3V:

ok d# 116 gpio-clr

The voltage at pin 4 should be +3.3V.