XO4 B1 C1 Changes
 B1 Electrical Fixes
These changes fix problems in the B1 prototypes:
 MMP3 B1 revision
 Increased Vin capacitance
The amount of capacitance local to each switching regulator was insufficient, causing high frequency currents in the power and ground planes. This was solved by increasing the amount of input capacitance at a number of voltage switchers:
- Add two 10 uF ceramic caps and one 0.1 uF cap in parallel with PC91, near PU8 (Vcore)
- Add one 10 uF ceramic cap in parallel with PC128, near PU11 (Vmem)
- Add one 10 uF ceramic cap and one 0.1 uF cap in parallel with PC75, near PU5 (+1.8V)
- Add one 10 uF ceramic cap in parallel with PC87, near PU7 (+3.3V)
- Add one 10 uF ceramic cap in parallel with PC52, near PU4 (+5V)
- Ferrites added to battery connector
- RF bypass caps added to SOC_RESET# line from EC
- Feedforward cap across R400, EC EDI SPI CLK voltage divider (done as ECO to ALL B1 motherboards)
 eMMC Power
Widening our options to deal with the SDHCI problem (ticket #12169), we:
- added a clamp which pulls +3.3V_eMMC to ground when power is turned off
- added a bypass to the eMMC power switch, in case we get eMMC_RST# working so well we don't ever need to power cycle it!
 B1 Layout Fixes
 Display Screws
The layout has to change to make room for display mounting screws intruding into the motherboard area.
 Correct IR PCB FFC Connector
The connector for the FFC cable to the IR PCB assembly had its pinout reversed accidentally in B1. This was fixed in B1 units by using a reversed FFC with an ugly bend.
- Ensure that CN5 has the correct layout.
- The pinout of CN5 has changed to be only 10 pins.
 B1 Mechanical Changes
 Display Mounting
The Display mounting screws in C1 will be the same as current XO-1.75 production. The B1 prototypes used a shorter screw to avoid damaging the motherboard. The motherboard will have to be modified to allow for an intrusive display screw boss.
 Speaker Mounting
This has to improve. It failed in 20% of the units in shipping air freight from QSMC to Cambridge!
 Touchscreen FFC Connector
The connector on the IR PCB will be strengthened to avoid the need to tape down the FFC to the bezel. This necessitates a change from 12 to 10 pins on the FFC to make room for the larger connector. The FFC pitch remains 0.5mm.
 Planned Feature Changes
 +3.3V SPI Flash ROM
XO-4 B1 switched to a +1.8V 2MByte SPI ROM for OFW. In version C1, this is switched to be a +3.3V part.
 External SD +1.8V support
In XO-4 C1, support is added for +1.8V external SD card operation.