Why has my MacBook Pro stopped outputting audio on external speakers?

Question

Since buying a MacBook Pro in April 2007, I had no problem playing recorded music and Internet radio on external analog speaker systems in two different houses. Suddenly this summer, the audio no longer plays through the external speakers --though it still works fine with the internal speakers. There were no major changes or accidents. The only technical issue I had was the recent malfunctioning of my laptop battery, which Apple acknowledged was defective and replaced yesterday. (I hoped that the problem might be resolved by the new battery. But it hasn't been.) Most of the discussions I've read about audio troubles with the MacBook Pro don't apply to this situation. (The most-discussed problem had to do with the internal speakers no longer working, often because the MBP's audio out port had inadvertently gone into digital audio mode.) My MacBook Pro is a 2.33 MHz Intel Core 2 Duo, OS 10.4.11, The mute button is not on. The speaker sound is up to max. And when I check the Sound status in System Preferences, the info line correctly identifies the speakers. The default ID readout is internal speakers. And the ID reads external speakers when I plug the external speakers into the headset/audio out port, But the sound plays only on the internal speakers, not on the external speakers. I miss listening to my music library and favorite NPR stations on a good sound system, where ever I go. I'd be grateful for any help. Thanks

Answer 1

If your computer was hot it wasn't asleep - it either didn't go to sleep or it work up after you put it to sleep. I've seen both things happen. First, read this article and follow the instructions.
1) For the next few days/weeks pay attention to the blinking light on the front of your computer when you close the lid. Don't put the computer into your backpack/case until it begins to blink. Wait a minute or so after it starts to blink to make sure it doesn't stop blinking - the signal it woke back up.
2) having followed the above instructions, if you take the computer out and it is hot again or if you take it out and discover it has powered down (you'll know this because when it starts up the battery will be drained and you'll see a progress bar over a ghostly display that will eventually become normal) immediately start the Console program and perform a search on 'sleep' and then 'wake'. This should bring up all the recent log files about sleep state changes (going to sleep and waking up). You should see one for when you put the computer to sleep and put it away and the next one should be just after you got it out. You'll find at least one though that shouldn't be there. That will tell you when the computer work up (when it shouldn't have) and might give a clue as to why.
One of the whys could be a magnet that is making the computer think the lid has been opened.