View source for XO 3 A1 ECOs

{{OLPC}}
These are recommended engineering change orders (ECOs) to the [[XO_3_A1|A1 prototype]] of the [[XO-3]] laptop.  This is NOT a list of changes from A1 to A2, that is [[XO3_A1_A2_Changes|located elsewhere]].

==Fix OTG connector==

The pinout on the USB OTG port needs to be swapped.

Done to some motherboards.  Motherboards which haven't been modified should have tape blocking the use of the port.

==Switch LCD Scan==

* Depopulate the 10K resistor in R200.
* Populate R189 with a 10K resistor.

Done to all motherboards.

==Fix Audio Jack==
We attempted to support TRRS headphones (ones w. integrated microphones) in the headphone jack.   Unfortunately, the engineer used the Nokia TRRS headphone/mic spec. instead of the one used by Apple, and as a result the external Mic. jack is crippled.   This ECO drops all support for integrated microphones.

* Depopulate R3

Done to all motherboards.

==Fix Camera==

* Swap an AO3402 into Q9

Done to all motherboards.

==Backlight PWM==

* Change PR128 to a 1K resistor.
* Populate PC122 with a 0.1uF capacitor

Done to all motherboards.

==USB OTG Power==
On almost all motherboards, PJP4 has been removed, disabling the ability for the USB OTG port to power the tablet.

If PJP4 is populated (don't do it!), there is a problem that power can leak back onto the USB OTG +5V line from the battery.  In order to fix this:

* Change PR92 from 7.15K to 69.8K
* Change PR108 from 10K to 100K
* Change PR97 from 5.1K to 52.3K
* Populate PR64 with a 10K resistor

This change has been made to most motherboards (even though PJP4 is removed).

==LCD Power Control==
The LCD digital power enable was unfortunately connected to a GPIO on the SOC which is asserted high on power-up.   This results in a visible flash of the backlight on power-up.

* Remove PR82 and R191
* Run a wire from TP66 to the pad of R191 attached to U5
* Run a wire from TP66 to the pad of PR82 attached to PQ40

This connects the LCDVCCENA signal to GPIO33 instead of GPIO138.  GPIO138 is still switched in conjunction with GPIO33, allowing non-modified motherboards to function properly.

Done to most motherboards.

[[Category:Hardware]]
[[Category:XO-3]]