XO Troubleshooting AV

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HowTo [ID# 275222]  +/-

This is the portion of the XO Troubleshooting Guide for diagnosing problems with the audio and camera components of an XO laptop.

Testing from Open Firmware

A stereo sweep pattern is output for testing the speakers/headset jack when running the Open Firmware hardware self-tests. A camera test, and a microphone test (where audio is recorded, then played back at low volume) is also included. These are activated by holding down the left side of the rocker switch (on the left side of the screen) when the laptop is powered on.

Also, the XO plays a startup tone from Open Firmware immediately after it is powered on. This is a good way to determine if sound support is working at a basic level (just turn it on and listen), but bear in mind that this sound may have been muted by the user. The volume of this sound can be adjusted by pressing the volume up/down keys on the keyboard at around the time when the sound is playing, and the resultant volume will be saved for next boot. It is possible that the user may have muted this sound by turning the volume all the way down.

Testing from Sugar

The "Tam Tam Mini" activity is a good source of audio for testing. The default sound source (guitar) is OK. Press the one of the "QWERTYUI" keys to obtain a sound. It generates a sound in both stereo channels.

You can increase the output volume of Tam Tam Mini using the rightmost of the four sliders in the upper left corner. Ensure that the laptop output volume is turned up using the "volume adjust" keys

The "Record" activity is useful for testing the function of the microphone and camera. The "Analyze" activity may also be used to debug microphone problems.

Sound from Open Firmware but not from Sugar

A bug in our operating system releases means that some badly-behaved activities or programs may break sound by muting one of the hidden software mixers. The result of this is that you'll hear sounds from Open Firmware with no problems, but not at all under Sugar.

After you lose sound, you can restore it by opening the Terminal activity and running the following command

amixer sset PCM 90% unmute

A more simplistic alternative is to install and execute the FixSound activity. This is equivalent to running the above command.

Both of these workarounds will restore sound once it goes away, but will not attack the root cause of the problem. The issue is likely to return in future, at which point you can execute the workaround again. The root cause of this problem will be addressed in future OLPC OS releases.

No sound through one of the speakers

If no sound is heard through one of the speakers, try using the headphone jack. If one of the audio channels is silent through the headphones, the motherboard probably needs replacing.

Re-install the software and repeat the tests to ensure that the problem is in hardware before replacing the motherboard.

If both channels are heard through the headphones, disassemble the top portion of the laptop and replace the speaker. If this doesn't fix the problem, replace the motherboard.

Suspect components in this case are static protection U67/U68, and the power amplifier, U44. Note that the laptop uses a class D amplifier, making it difficult to directly measure the output.

No sound through either speaker

If no sound is heard through either speaker, try using the headphone jack. If the headphones work fine, then disassemble the top of the laptop and try replacing the speakers.

If replacing the speakers doesn't fix the problem, replace the motherboard.

Suspect components in this case are the power amplifier, U44, the headphone jack, and the +5V supply. Note that the laptop uses a class D amplifier, making it difficult to directly measure the output. Inserting/removing headphones should toggle the signal on pin 2 of Q42, turning off/on the power amplifier. If that signal doesn't toggle, try replacing the headphone jack (CN3). Check the operation of the USB ports. If they work, then the +5V supply is working. If USB ports are also non-functional, the +5V supply may not be working. Check U26, D126, and L28.

Speakers and Headphones don't work

If no sound is heard through either the headphone jack or the speakers, the motherboard probably needs replacing.

Re-install the software and repeat the tests to ensure that the problem is in hardware before replacing the motherboard.

Garbled sound or rattling from a speaker

When a (loud) sound is played, one (or both) speakers rattle or garble the sound.

Use the headphone jack to verify that the sound isn't garbled through the headphones. If it is, try re-installing the software and repeat the tests. If the problem persists, replace the motherboard.

If the audio sounds fine through the headphones, disassemble the top of the laptop to access the garbled/rattling speaker. If the speaker is loose in it's mount, try pressing it back. If this repairs the problem, use hot glue or contact cement to ensure that it doesn't come loose again. If the speaker continues to sound bad, replace it.

No sound through one or both headphone channels

If the speakers function correctly, yet no sound is heard through one or both headphone channels, the headphone connector on the motherboard needs replacement.

If the speakers don't work, see Speakers and Headphones don't work.

The microphone doesn't work

If the built-in microphone doesn't work, try using an external microphone.

If an external microphone works, ensure that the microphone connector (CN15) is well seated. Try replacing the microphone. If that doesn't fix the problem, the motherboard will need repair.

The likely suspect on the motherboard is the microphone jack (CN5). The internal microphone is routed through it.

An external microphone doesn't work

If a known good external microphone plugged into the microphone jack doesn't work, the motherboard will need replacement.

The components likely to cause this are L23 (a ferrite) and D13 (a 5.1V zener). U24 (the DC switch) may also cause this problem. In early production models, a low voltage DC source (such as a battery) plugged into the microphone input with the wrong polarity would destroy D13. In later models this is still possible, but it requires a much higher voltage.

Errors communicating with the camera

If there are errors when trying to use the camera, or the image obtained from the camera is black, disassemble the top of the laptop and take a look at the camera connector (on the back of the motherboard, underneath the camera). The latch on this connector occasionally opens. Remove the motherboard. Reseat the cable and latch the connector. Reassemble and repeat the tests.

If this doesn't fix the problem, replace the camera. If replacing the camera doesn't solve the problem, try re-installing the software, then replace the motherboard.

Suspect components on the motherboard are the CaFE ASIC and the camera voltage regulator, U48. It should be providing +2.8V on pin 6 and +1.8V on pin 1.

B4 camera hardware may be susceptible to right side case flexing/pressure due to shorter than ideal camera ribbon connector. Camera image may display purple/green, stall, or just blank out – gentle pressure on the right, just below the camera affects the image (may make it better or worse). Disassembly of the top of the laptop and re-seating the cable may help. --garycmartin

Images from the camera are black

See error communicating with the camera.