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iPhone 3G repair

Discussion in 'Troubleshooting and Repair' started by quantumtangles, Jan 12, 2013.

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  1. quantumtangles

    quantumtangles

    152
    3
    Dec 19, 2012
    iPhone 3G does not turn on following a battery change. When the battery is connected, it does not power on, nor does the screen even flicker.

    It also shows no signs of life when connected to a mains charger.

    Experimented on it a while back to make a solar charger for it...soldered additional wires onto the logic board power input terminals, but they have been removed. The phone worked after the solar charger debacle but stopped working following a battery change.

    Excess solder was also removed using de-soldering wire. No obvious cross traces of solder visible (terminals look intact under a magnifying glass...and just about isolated from one another). De-soldering may have caused components or solder joints underneath the logic board to fry, don't know. Be surprised if it was not a double sided board.

    There are 4 relevant logic board terminals matched by 4 pins on the battery. Only the terminals far right and far left are the power terminals. The others probably relate to short circuit protection and/or voltage regulation to prevent battery overcharging.

    Outer two terminals relate to power (+ve and -ve). Inner two terminals do not (short circuit protection and battery voltage regulation).

    Tested flexible screen connections, and they are all in place, so power does not seem to be getting onto the logic board.

    The reason for this post is that I did a continuity test on the positive and negative terminals of the logic board (the terminals where the positive and negative terminals of the battery press against the logic board power input terminals).

    There IS a continuity signal between positive and negative logic board terminals. Wtf?

    Strongly suspect this should not be the case but hopefully one of the experienced engineers here can set me straight if that is wrong. Cannot find a schematic online for this device (Apple iPhone 3G).

    Should there be continuity between +ve and -ve logic board input terminals? Surely not. Any suggestions about how to approach repairing this thing much appreciated.
     
    Last edited: Jan 12, 2013
  2. Yoa01

    Yoa01

    214
    0
    Jun 18, 2012
    To charge an iPhone 3G, the negative usb data pin should be at 2.8v, positive at 2.0v. This is a notification to the iPhone that it is connected to an external charger, and will thus charge. Otherwise, nothing will happen. Measure these voltages and make sure they are correct. If not, you'll need some resistors: 33k on pin 23, 22k (or 47k, depending on voltages) on pin 16.

    Note: I have no actual experience playing with these, but I do know the pinout and generally how voltages work with the logic system.
     
  3. quantumtangles

    quantumtangles

    152
    3
    Dec 19, 2012
    Thanks Yoa01.

    The iphone was not working but that did not really bother me. What ****ed me off was that I could not figure out why it was not working.

    Continuity tests (between positive and negative terminals) on the logic board showed the two terminals were actually connected to one another...oops.

    I removed all soldering traces from earlier experiments (in case I had accidentally bridged across clearances). It all looked fine, but I was still getting continuity between positive and negative logic board terminals. In other words, the four pins of the battery (which press against the logic board terminals) would have been pressing against 'connected' positive and negative logic board terminals...serious and delirious.

    After completely taking the phone apart (and I mean completely and utterly taking it apart), I finally figured it out (you wont be seeing me using this phone anytime soon).

    The logic board was cracked...stress fractures underneath the logic board terminals. This ship has sailed.

    Everything is connected to ground...so I need a new logic board, but at least I know what was wrong.

    Thanks for your post :D
     
  4. Yoa01

    Yoa01

    214
    0
    Jun 18, 2012
    Sorry I couldn't help, but I also couldn't have known that issue! This is why *I* don't experiment on $600+ equipment :)

    I'm sure it would be a fun show to plug it into a slightly higher voltage power source. Who needs fireworks when you have Appleworks? ...that was lame. Sorry.
     
  5. quantumtangles

    quantumtangles

    152
    3
    Dec 19, 2012
    Curiosity hurts. I suffer particularly badly...not all the time...in phases. Physical and mental pain...do almost anything to prevent it, hence taking expensive devices apart. But at least I now know, and have a cool display for future projects. Can salvage the camera as well for a project.

    Not sure how the other components can be put to use. Maybe try to make a phone :D
     
  6. Yoa01

    Yoa01

    214
    0
    Jun 18, 2012
    Something I've found is that almost everything oscillates. Maybe you can build a phone-sized instrument? haha
     
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