external microphone

Depends on exactly what's wrong with the device in the first place. If you can't hear anything even over headphones then it's likely the audio chip is buggered, and since audio of any sort -- externally sourced or otherwise -- is handled by that chip it probably wouldn't do you any good. If you're going to try see if you can demo something before shelling out any money.

 

So, it works if you leave it off for half an hour, then turn it on, and it works for a few minutes? When you say "turn off" do you mean just put it to sleep or actually turn the whole thing off?

It sounds to me like a heat issue, like a cracked solder joint that loses connection when it heats up or something, causing a short. The screen goes out too?

 

I doubt opening the phone would do much good. Most of the stuff in the iPhone is surface-mount; you'd need special equipment to work on it. They aren't easy to open either. You need a spudger just to separate the shell. (If you're bound and determined, ifixit.com has the tools you need, and a disassembly guide too.)

 

I wouldn't touch it with a 10-foot spudger. I'm pretty comfortable with a soldering iron and old school ICs and stuff, but surface-mount technology is way out of my league when it comes to electronics. Plus, even with the right tools you have to be really careful when you separate the case or you'll snap something. I might open up a dead one for curiosity's sake, but I'd have no illusions I could do anything about bringing it back to life unless it was something stupidly simple like a ribbon cable or molex came loose. Which I seriously don't think is the case here.

However, I just came across this on iFixit:

If I'm reading the inference right, a faulty headphone jack can cause your sound to completely disappear whether or not you're using headphones. Which would make sense now that I think about it; if there's a short in the jack the phone may think phones are plugged in, even if they aren't. The result would be no sound. The one thing I can think of that would confirm this is to call someone -- or call yourself on your house phone. If you can hear yourself talking into the iPhone from your house phone, but can't hear yourself respond on the house phone from the iPhone (the mic isn't disabled unless it detects a 3-pole jack which indicates the presence of an inline mic) then the jack is probably your problem.

Here's a link to instructions on how to disassemble the iPhone 3G if you're feeling brave. To get more specific, here's a manual on replacing the headphone jack. MAke sure you have a precision Philips #00 screwdriver on-hand, and you'll need a spudger. They also sell the headphone jack assembly.

 

You're welcome. Good luck with it if you do decide to brave the operation. It doesn't actually look all that difficult if you're somewhat familiar with digging around inside electronics -- at least there's nothing to solder. It's mostly screws and ribbon cables and a lot of steps just to get at the jack assembly. Pain in the ass, but doable.

 

It would depend on what the problem is exactly, and with that assembly it could be anything from a ribbon cable that's partially out of its slot, a cracked trace, one of the components within the assembly flaking out and causing a short (which seems to include volume switches, mute switch, and power button), or a cracked solder joint inside the jack assembly.

Coming at it from a logical point of view I don't think it's dirt. It would have to be moist or electrically conductive to cause a short, and there would have to be a lot of it -- like, enough to see with half a glance down the hole -- to cause a short. Liquid is possible I suppose, but again you'd be able to see if it got wet, because Apple place a small piece of litmus paper inside the jack that turns orange when it comes in contact with moisture. (It's how they know if your device has been water damaged when you take it in for warranty repair after dunking it in the toilet. )

Assuming you see no dirt and the paper is still white, it sounds to me like an internal short. First thing I'd do is take a toothpick, stick it partially in the jack and start wiggling it around (gently!) while playing music and see if the music starts coming on at any point. While you're at it, try playing with the mute switch, volume buttons and power button to see if moving any of them around causes the music to cut in at any time. That should also help pinpoint the location of the short.

Even if you find it though there's much hope in doing anything about it without going through the aforementioned repair steps.

Just for the hell of it, if you have a can of compressed air, turn off your phone (completely off, not just to sleep) then blow some air down the headphone jack through the little straw attachment you get with the can. If there's any moisture, or perhaps some little metallic bit that might be causing a short, that ought to help dry/dislodge it.

 

So it's a heat issue. Heat is expanding a connection somewhere, and a break in that connection is separating under the heat, causing the short. Either that or there's a pocket of air that has developed under some adhesive, thermal paste or epoxy on a critical chip in there that's becoming superheated and overheating the chip, which is why you need that cooldown period.

But I'd stake money on it being a heat issue of some sort. Don't even bother trying to diagnose that. You'd have to somehow be able to get in there with a mutlimeter to test traces while the unit was still running.

This still doesn't necessarily rule it out as being a headphone jack issue though.

 

Well, the iPhone, at least prior to the 4, had somewhat low tolerances for excessive heat (something like 100°F or something); leave it on your dash on a hot Texas summer day and it would probably be dead by the time you get back.

That said though it still shouldn't cause problems if it's not in direct sunlight for extended periods of time while in heavy use. The problem could be made worse if you're using a case that doesn't allow heat to dissipate easily though.

In either case though yes, it's almost certainly a heat issue somewhere. When it dies try sticking it in the fridge for 5 or 10 minutes, see if it comes back to life faster.