XO4 C1 ECOs
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 R417 and R420 with zero ohm resistors.
- Remove Q55.
- Replace Q54 with a 2N7002W. Run a wire from Q55, pin 3 to Q57, pin 3.
- Remove C498
- Change R414 and R415 to 330K
- Change C420 and C496 to 0.1 uF
- Replace Q50, which has been removed, with an AO3402.
All components mentioned are located on the "bottom" side of the PCB next to the external SD slot. Waveforms showing the problem and the timing of the fixed circuit are available.
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 higher quiescent power, but otherwise works fine and halves the soldering required. The board ID should also be modified.
- Replace R420 with zero ohm resistors (anything less than 50 ohms will do).
- Remove Q55.
- Replace Q54 with a 2N7002W. Run a wire from Q55, pin 3 to Q57, pin 3.
- 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.
