XO 1.75 A3 ECOs
These are recommended engineering change orders (ECOs) to the A3 prototype of the XO-1.75 laptop. This is NOT a list of changes from A3 to B1, that is located elsewhere.
SMBus Pullups
These correct a mistake omitting the pullup resistors for the SMBus between the EC and the battery charger. It has been done to all boards.
- Add a 1.3K resistor between PR200 and +3.3VSUS (available at PD31, pin 2).
- Add a 1.3K resistor between PR201 and +3.3VSUS.
External SD Power
This corrects a wiring error. It has been done to all boards.
- Tie PQ64.2 to Q22.2
Audio Power
This corrects a wiring mistake (<trac>10974</trac>).
- Wire +3.3VA_AUDIO (U24.5) to +3.3V_AVDD (the side of C218 closest to the codec).
It has not been done to many boards. Marked AUDIO on the tag.
RTC Power
This corrects the inability of the RTC to maintain data across a power-off (<trac>10999</trac>).
- Change R29 (top side of board, underneath the RTC) to 330 ohms
- Add a 10 uF capacitor in parallel with C227
It has not been done to many boards. Marked RTC on the tag.
Keyboard Touchpad Routing
This connects the keyboard and touchpad to the Security Processor instead of to the embedded controller. It is necessary for using an A3 with OFW Q4B11 and later.
- Remove R351-R354 (zero-ohm resistors)
- Install jumper wires or zero-ohm resistors at R355-R358
One fast way to do it:
- Mark the unpopulated pads R355-R358 with a pen so you can identify them easily after having removed the adjacent zero-ohm resistors.
- Remove R351-R358 by putting a blob of solder onto the end of a soldering iron and touching the molten blob to the resistors. They will lift easily.
- Strip an inch of insulation from a piece of rework wire.
- Holding the other end of the wire, place the bare wire across a pair of pads, touch the iron to it to solder it down, then cut to length with an XActo knife. Repeat for each of the 4 pad pairs R355-R358.