QUOTE(Jigsaw2793 @ Jun 17 2012, 10:09 PM)
So i'm new here, howdy. I have a bit of a problem. I have a dead xbox next to me, or so I think it is. A while ago, I soldered a 120mm fan to the thing to keep it cool. It worked well for about a month, then the dreaded E74 came back. So i took it apart and did the whole heat gun business. I went to turn it on and...no power. I was looking around making sure no capacitors busted. Everything was good. I'm not a moron, I covered the areas I wasn't aiming for with foil. Then i looked underneath and found that the ground wire from the fan came loose. Ok, I AM an idiot. I tried to solder it back on, but still no power to the system. So my question is there anything I can do about it? Or is it just trash now? My guess is that the motherboard just shorted out. Thanks for any suggestions.
This will probably get moved to General Hardware eventually.
Well first off, what was your process? Did you use flux, thermocouples, and a preheater when you heatgunned it?
If not, I don't know what kind of results you were expecting. But here goes my diagnoses:
Using only the heatgun would cause localized thermal expansion and the board would flex. If it flexed while the solder was liquid (or even when it wasnt) many solder balls could have lost contact with the board under any of the chips (possibly causing what you're describing).
Not using flux would leave the solder balls you were trying to liquify very brittle and covered in oxidation. They wouldn't have lasted long if it worked at all.
Not using a thermocouple could mean the heat over the chip was not distributed and the temperature was likely far too high. This could mean bridged solder points.
The most likely result in my opinion though is that because the air flow from a heatgun is very high (in comparison to a reworking station with adjustable air flow settings) and because the heatgun has a constant heat setting which is often extremely high for this use, I can bet you it blew critical surface components right off the board. There are very tiny resistors and capacitors all around the GPU and CPU, and all over. In my experience, an exploded electrolytic capacitor (big battery lookin ones) hardly ever keeps the Xbox from functioning, but one tiny capacitor or resistor gets blown off and that thing will not turn on. If this is the case, you'll need to identify where the component is that blew off, and you'll need to find a donor board...unless you can find where it blew lol.
Also just take a look around the board to see if any solder splashed anywhere and bridged anything.