XO 1.75 B1 ECOs
These are recommended engineering change orders (ECOs) to the B1 prototype of the XO-1.75 laptop. This is NOT a list of changes from B1 to C1, that is located elsewhere.
Fixing PWR_LIMIT_ON
A status signal from the MPPT circuitry to the EC was configured wrong.
- Remove PR227
- Change PR244 from 100K to 4.7K
- Remove PR229 and place a 0.1 uF, 6.3V 0402 capacitor in its location
Marked as "MPPT OK" on the tag.
Possibility of Shorting Vin
If a large force is applied to the back panel, near the DC power input, there is good chance that the heat spreader will short the main internal power rail. This will do "Bad Things"™ to your motherboard.
- Place a piece of tape (electrical or cellulose) on the underside of the heat spreader, on the corner nearest the DC Power jack.
This has only been done to the laptops w. touchscreens, and a dozen or so others. We recommend marking a "NS" in the battery compartment.
RTC Problems
The RTC clock doesn't come close to meeting its published specifications. On some laptops, it occasionally loses the time when the main battery is removed.
- The IDT1338 datasheet calls for a minimum fall time on the RTC supply of 300 uS. The existing circuitry guarantees a 500 uS fall time, but some chips require an even slower power-down to retain data.
- Place a 10 uF, 6.3V capacitor in parallel with C227, or replace it with a 22 uF, 6.3V cap.
This has been done to all laptops on which the problem was detected after run-in.
Fix MPPT
This extends the range of input voltages which the MPPT algorithm can use.
- Change PR234 to 150K
- Change PR235 to 220K
This was done to most B1 units, with the exception of twenty-six or so identified by a green dot on the hinge cover. wad has the serial numbers of laptops missing this ECO.
Increase Bulk Decoupling
This fixes a problem seen on some boards w. Sandisk eMMC chips where trying to turn it on results in two fast blink of the red battery LED, cycling indefinitely. The problem is due to the +3.3V power supply shutting down when loads are added suddenly.
- Populate PC54 w. a 22 uF, 6.3V cap (or higher). This should be a ceramic cap.
This has already been done to around a dozen motherboards, as needed for reliable booting.
Enabling Antitheft
By mistake, the resistor which disables the OFW SPI Flash antitheft circuit (to allow for ISP reprogramming in the repair center) was populated.
- Depopulate R92
This has not been done on any motherboards.