Category: Technical

I recently purchased an iPhone 3GS that had a cracked back housing. I found a replacement part on eBay for $18 shipped.  I found a nice 720p youtube video that really helped my confidence before disassembling the iPhone.

Replacing the back is probably the most difficult repair you can make to the iPhone. It requires that you take everything apart except the front assembly (glass/digitizer). The repair took about 2 hours. It will be much quicker next time (yah, I’ll probably help other people fix their phones too) since I know what I’m doing now. After putting everything back together, I ran into a few problems, one of which had me very nervous for a bit.  Here’s how it went down…

I replaced the back and closed up the iPhone.  Then I discovered that my sim card was not getting recognized.  It was as if the iPhone didn’t even know when I ejected and reinserted the card (which turned out to be the case).  Then I did something stupid.  I got distracted.  🙁  I forgot to completely power down the iPhone before I opened it again.  I discovered the sim problem but there wasn’t much I could do about it because upon reconnecting the LCD and front assembly and closing the iPhone I could hit the power or home button which would light up the screen but it would only light up black.  It was like the motherboard was not sending data to the screen.  I will admit that at this point I was a little worried.  I thought I might have damaged the motherboard somehow but I knew that it had been working only moments before and I thought it unlikely that disconnecting the LCD while the iPhone was on would really do any damage.  I started thinking worst case scenario, I have to buy a new motherboard ($100 to $150).  Not the end of the world but certainly one of the most expensive mistakes I’ve ever made with electronics.

So now I had 2 problems to solve and this was supposed to be a 20 minute project!  I had another hunch that shutting down the iPhone and rebooting with everything attached might solve the LCD problem and it did!  The only problem was that I couldn’t figure out a way to shut down the iPhone since the digitizer was unresponsive and I couldn’t see anything on the screen.  I decided to disassemble everything again to disconnect the battery.  Then I reconnected everything and rebooted and the LCD problem went away.  Yay!

There is an easier way to shut off the iPhone without taking everything apart.  The battery connects to the motherboard via 2 contact points on its back side.  When looking at the front of the board they are in the bottom right area just south of the vibrator.  You can unscrew the 3 motherboard screws along the right edge of the board and loosen the ones on the left side.  Then you can gently lift the motherboard on the right side which will disconnect the contact points.  Keep it disconnected for a good 10 seconds to let the motherboard clear out.

Finally I was ready to tackle the sim card problem.  Earlier when I opened the iPhone looking for the problem with the sim card I noticed that the motherboard mounts a hair lower in the new back housing preventing the sim card activation circuit from opening.  This seemed strange to me since I know that this is an OEM part.  How could it be that different?  But take a look at the picture…

With the sim tray fully inserted, it didn’t press the tiny v-shaped wire that opens the circuit. Every time this circuit is opened the iPhone tries to recognize the sim card. After pondering on the problem for a bit, I decided that it would be better to modify the sim tray than the wire on the motherboard. After all, if I messed up, sim trays are cheap. I ended up cutting a tiny sliver off of the end of an old gift card. It was the only thing I could find around the house that was thin enough. I super-glued it to the sim tray which worked out nicely…