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.

Contents

Start Here

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 battery is a LiFePO4 battery, with a yellow label, see the LiFePO4 recovery procedure.

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 indicate the laptop thinks it has power ? With a battery inserted, the battery LED should turn yellow or green within a minute of applying power. In this case, the laptop probably has a startup problem, not a power problem.
  • Otherwise, the motherboard needs replacement.
Suspect components are the fuse F1 (2A) and diode D21 (3A schottky) on the motherboard protecting the DC input. If the fuse was blown, check diode D123 (3A schottky) and diode D118 (38V zener) 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 commands 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

There are a number of possible causes for lack of battery presence. Here they are, in the order in which they should be checked.

Unplugged cable

The battery connector in the bottom part of the laptop

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.

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

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. Use a known good battery to ensure that the problem is with the battery and not the laptop.

A battery in this condition can be detected by watching the output of see-bstate.

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. If the laptop cannot communicate with the known good battery, and you have already checked for an unplugged cable or broken wire, then the error is in the laptop motherboard and it will need replacement.

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 prompt 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.

Software Tools

olpc-pwr_log

Currently this tool (a Linux script) 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

The script will wait until it detects a battery and then begin to log various parameters via the olpc-battery subsystem. If your battery is really low and the EC is using trickle charge rather than main charge then the script will appear to be still looking for a battery even though the yellow charge light is on. Once the EC finishes trickle charging it will report that a valid battery is present and the script will continue.

The output of the script is both to the screen and to a file. The file name is 'pwr-<date>-<gauge ID>.csv'. Gauge ID is a unique ID number that is contained in the gas gauge of each battery.

More details can be found here

batman.fth

Batman.fth is a forth script that is available from http://dev.laptop.org/pub/firmware/scripts/batman.fth. To use it you must load it at an Open Firmware (OFW) prompt. Getting to an OFW prompt requires a developer key. To use:

  1. Place batman.fth on a USB key
  2. Insert the USB key into the laptop XO (while it is turned off)
  3. Start the laptop
  4. Enter Open Firmware by pushing the ESC key while the laptop is starting up.
  5. At the 'ok' prompt, type:
fload u:\batman.fth

The batman script may be stored on devices other than a USB key. It is loaded with the 'fload' command, which must specify the storage device where bathman.fth is located:

USB disk:
 fload usb:\batman.fth
SD card:
 fload sd:\batman.fth
NAND flash (root directory):
 fload nand:\batman.fth

Once loaded you run the commands in the script just like any other OpenFirmware command. If you turn off the laptop, you have to repeat the loading process.

Key tools in batman.fth

The following is a list of useful tools in batman.fth with a brief note how to use them. Some of these commands require that the EC be put into reset prior to running them so that the EC battery management system is disabled. The 1w-init command does this. After the 1w-init command is used all keyboard, touchpad and button activity is disabled. Including the power button. Any command requiring a 1w-init will require that any further commands be invoked using the processor serial port. To power off the laptop afterwards, you will have to remove both external power and the battery.

  • 1w-init
Put the EC in reset and prepare the system so that Open Firmware can talk directly to the gas gauge chip in the battery. All keyboard, touchpad and button activity is disabled after this command. Required prior so some of the other commands.
  • see-bstate
Continually prints the EC 1-wire communication state machine index. Useful for determining if the EC can talk to the battery gas gauge.
Does not need 1w-init.
ok see-bstate
  • bat-recover
Does PWM on the charge enable line resulting in a psuedo-current limited charge of the battery. Streams the battery temperature, currrent, voltage and accumulated charge register (ACR) to the screen.
Automatically runs 1w-init
ok bat-recover
  • bat-set-low
Zeros out various values in the battery's gas gauge EEPROM forcing the EC to resync with the state of the battery. Useful if your battery is marked as full when it really is not.
Needs 1w-init
ok 1w-init bat-set-low

Linux battery subsystem

More information needed here

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