Water Damage: Works for a little while...
I have an iPhone 4S that has water damage. The power/lock button doesn't work anymore, but if I plug it in it will boot up. It will work perfectly (minus camera) for about 5 minutes and then it will pop up with the "Temperature" warning and will stay on that until the phone is turned off and back on or until it dies. I have never really done any "water damage" repair, but I've listed this on eBay and a ton of people want it, so I am sure it is repairable...Wo
After testing it out a couple times, I did take the board out and clean it with the 92%...there's not any corrosion left on the visible parts of the board. I did not, however, remove any of the EMI shields...
The iPhone 4S would have a thermistor (a thermal dependant resistor) which is how the iPhone can measure temperature. For most thermistors and most definitely this one the resistance decreases due to the rise in temperature, the micro-controller can measure this resistance and act accordingly. Water obviously conducts electricity to a point, you may have some vapour on this input which is slightly rising the resistance just enough to make the iPhone 'think' it is hotter then it actually is.
You can use one of these 'dry bags' that iFixit owns or, a rather more ingenious way is to put your open iPhone into a bag of dehydrated rice overnight, whilst leaving it in a dry, warm area like the drying room in your house. The rice will absorb the water vapour and should solve the problem. That would be the most logical explanation and the most suitable solution.
Hope this helps!
If there is enough water damage that there was visible corrosion on the board, it is likely that there is similar corrosion under the EMI shields. Removing these shields is not a good idea, as you will likely break the logic board in the process.
Your best bet may be an ultrasonic cleaner. These are often sold as jewelry cleaners, but when used with a high purity isopropyl, will ensure that every microscopic bit of water vapor, and often the corrosion that goes with it, will be scrubbed away.
These can be a bit on the expensive side to get the high quality ones, but if they work, almost all of them are less expensive than a new phone.
Worth noting that I never suggest using these except as a last resort. While they can sometimes work miracles with phones that no longer work, they can just as easily ruin a phone that simply needed to be carefully dabbed out, and put into a bag of rice.
Hope this helps. I chose to invest in an ultrasonic cleaner for my cell phone repair shop, if there is a local tech repair shop around, it's possible they've invested in one as well.
Mobile Rapid Response Unit
Take the back off the phone.
Take a portable hair dryer and put it on warm.
Let the hair dryer blow warm air across the RF shields
and logic board and all the iphone guts for like....a day
or two. It's the hours-n-hours of blowing warm air across
the parts that dries it out thoroughly. The rice trick is good
but it doesn't drive out any moisture. Rice will only absorb
moisture that happens to evaporate into the surrounding air.
Liquids in small spaces may not evaporate easily without
forced blown air.
I read the comment from pollytintop, and I agree.
The proper "rules of engagement" for approaching and fixing water damage involve the complete removal of water and assessment.
Sadly, this implies dismantling the water damaged device.
Water itself isn't damaging: electricity is. And water reroutes electricity in every point of the iPhone where it's not supposed to go, thus, wrecking havoc with the water logged device.
A lenghty stay in a Thirsty Bag, or, lacking that (and only if you can't afford getting one, I'm listing the possible avenues in order of efficiency) a cup filled with silica bags in a dry cupboard , or, failing that again, a cup filled with rice in a dry cupboard is always a good start.
Then comes the dismantling: open carefully your device. You'll need a special screwdriver, included in this kit, along with two new, philips headed, screws. Be careful: the iPhone 4S is filled with little, tiny parts.
Follow the guide for battery replacement: you're surely going to need a new battery, as yours was shorted up, and it'll always get a really short life.
Since you're there, clean everything with isopropylic alchol, keep everything dry, remove traces of weird corrosion, or even fungi (but be careful).
Then, close everything up and reassess.