XO Troubleshooting Battery

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This is the portion of the XO Troubleshooting Guide for diagnosing problems with the battery and power on an XO laptop.

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What problem are you experiencing with your laptop ?

The laptop won't run using the battery

If the laptop functions fine using a known good test battery, the battery should be replaced.

If the laptop doesn't function from a known good test battery, see Diagnosing Battery Problems.

The battery light is flashing red

If the battery light is flashing red, this usually indicates an error with the battery. Try a full reset. If the problem persists, then the battery should be replaced.

If the replacement battery shows the same flashing red battery charge light, see common causes for lack of battery presence, below.

It is possible to obtain more information about the battery, and possibly repair it. See below.

The laptop can't charge the battery

If the laptop can charge a known good test battery, the battery should be replaced.

If the laptop can't charge the known good test battery, see Diagnosing Battery Problems.

The laptop won't run using the power adapter

If the laptop runs fine using a known good power adapter, the power adapter should be replaced.

If the laptop can't run from a known good power source:

• Does the battery charge LED still indicate the laptop thinks it has power ?
• Otherwise, the motherboard need repair:
  • Check the fuse (F1) and diode (D21) on the motherboard protecting the DC input
  • If the fuse was blown, check diode D123 and 38V zener diode D118 to see if they are OK.

The laptop emits a high pitched whine when using the power adapter

Working on this one

Diagnosing Battery Problems

Charging of the battery, and interpretation of the front panel buttons, is under the control of a separate microprocessor in the laptop, the Embedded Controller (EC). In order to ensure that battery communications are being properly handled, we must first establish that the EC is operating correctly:

Did the EC boot?

Follow the Full Reset procedure, and check to see if the battery LED flashes orange momentarily after reapplying power.

If it didn't flash at all, you probably have a broken motherboard. If it flashed another color (red or green), then you probably have a problem with the LED driver circuitry.

Does the EC recognize the battery?

When a battery is inserted into the laptop, the EC reads information about that battery from a integrated circuit inside the battery. If the EC does not receive valid information from this read, it will either assume that a battery does not exist, or report an error. The following tests tell if the EC is talking the battery correctly.

Does the battery light respond to changes in external power?

When you apply external power, the battery led should light up in one of four states:

• solid green - indicates a fully charged battery
• solid yellow - indicates a battery being charged
• solid red - indicates a battery in dire need of charging
• flashing red - indicates a battery error. See above and a detailed explanation below.

If the battery light does not indicate one of these states (e.g. nothing lights up) then the battery is not being recognized. If you get a solid battery light then the EC has successfully read the battery gauge. If the battery light stays unlit then either the battery is not recognized or the data read has confused the EC. Use one of the following methods to manually check for battery presence to determine the problem.

Checking for battery presence

The following methods may be used to manually check for battery presence.

Using Linux

Linux has an interface to the laptop's battery subsystem. Its available via sysfs at /sys/class/power_supply/olpc_battery/. The value of 'present' indicates if the EC thinks a battery exists. To check this value use the 'cat' command in the terminal app or at a vtty:

cat /sys/class/power_supply/olpc_battery/present

Using OpenFirmware

You will need a developer key for the laptop. Open Firmware has command that will talk to the EC and read the current battery info. This command is watch-battery. At the Open Firmware command prompt do:

ok watch-battery

If EC thinks a battery exists you should see a single line that gets updated with various pieces of battery information. If a battery does not exist then that will be indicated with a 'No battery' rather than battery status info.

Using OpenFirmware and batman.fth

You will need a developer key for the laptop. Batman.fth has comands that can interrogate the state machine of the EC's 1-wire interface. This allows you to see what's happening on the 1-wire bus. The command for this is see-bstate. If a battery is not detected the numbers printed will cycle between 0,1 and 2. Numbers other than that indicate the EC has detected a battery.

Common Causes for lack of battery presence

Unplugged cable

Check to see that connectors CN21 and CN22 on the motherboard are firmly plugged in. There is a second connector, hidden in the bottom part of the laptop.

The battery connector in the bottom part of the laptop

Broken Wire

If no batteries are detected, a break or bad connection between CN22 on the motherboard and the data pin on the battery connector results in no 1-wire communication (seen as this problem). Check continuity of the cable with an ohm meter.

add pictures

One-wire Communication Error

The sensor inside the battery could be malfunctioning or the output from the EC could be corrupted from a manufacturing defect. Try swapping in a known good battery and trying the suspect battery in a known good laptop.

If the laptop cannot communicate with the known good battery, and error is in the laptop motherboard then it will need replacement.

Bad data in battery EEPROM

Normally if the data in the EEPROM has been corrupted a flashing red LED error will result. However, depending on the corruption it may be possible to confuse the EC. This can be detected by watching the output of see-bstate.

Battery LED is flashing red

Flashing red LED indicates that the battery subsystem has detected an error. Open Firmware has a command that will read the error code from the EC. The command for this is 'ec-abnormal@'. At the Open Firmware use the following to view the error code.

ok ec-abnormal@ .

Note the '.' at the end. This is required to print the error code.

The error conditions should be listed...

Battery fails to charge?

Checking the actual charge level

olpc-pwr_log is a Linux bash script that allows you to measure the amount of charge delivered to or extracted from the battery. It can be used to determine if the battery is performing at its rated capacity.

Laptop abruptly shuts off before battery is capacity reaches < 10%

See above

Experimental LiFePO4 Recovery Procedure

Problem Symptoms

A small percentage of LiFePO4 batteries are exhibiting a problem where they do not charge correctly. The parameters that the EC watches while charging change in such a way that the EC thinks the battery is full and marks it as full. On some batteries this seems to happen in the first few minutes and on others it happens much later on. The end result in all cases is an abrupt shutoff when the voltage on the battery drops below the critical level where it can sustain operation.

Software Tools

olpc-pwr_log

Currently this tool is located at http://dev.laptop.org/~rsmith/olpc-pwr_log

To use olpc-pwr_log follow the following procedure:

1. Copy (or download) olcp-pwr_log to the XO. It does not need any special priviledge
2. Start it

batman.fth

Batman.fth is a forth script that is available from [1]. To use it you must load it at an Open Firmware (OFW) prompt. Getting to an OFW prompt requires a developer key. At the OFW prompt the script is loaded with the 'fload' command specifying the storage device where bathman.fth is located. Examples:

USB disk:

fload usb:\batman.fth

SD card:

fload sd:\batman.fth

Nand:

fload nand:\batman.fth

Once loaded you run the commands in the script just like any other openfirmware command.

Linux battery subsystem

More information needed here