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Fourth generation iPhone. Repair is straightforward, but the front glass and LCD must be replaced as a unit. GSM / 8, 16, or 32 GB capacity / Model A1332 / Black and White.

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Saving latest (since sync) data when the power supply fails


my iPhone4 has entered a failure mode since the batts went to zero mid call.

It's now in a restore loop - apple logo only then reboot cycle - (BUT only when powered by a pc usb). When powered by an Apple charger the normal boot up occures and completes with the iTunes restore sync picture. It will not turn on at all on batteries alone.

Apple and I have checked the battery, its fine and sitting charged at 3.9V. The additional charging on mains allows the iphone to draw 1A not the 500mA on usb - this makes a difference to the turn on behaviour as above i believe. I tried making special cable to transfer from mains charger to pc usb after the device was 'on' but this doesnt help. The cable works in forceing the data lines to 2.5V and 2V to indicate fast charge and forces the iTunes Restore mode but the pc usb does not reconise the device, sees a device but cant tell what it is - maybe another problem also or just the fact that the breadboard cable cant communicate at the speed required. Replacing the battery has no change.

I have tried iRecovery under various device status. I can communicate with the iphone and setenv, reboot etc. The standard setenv/save/fsboot solution to the restore loop doesnt work, nor does setenv/save/reboot. iRecovery reports 'gas gauge SWI low' problem.

The data will be on the logic board I guess in flash so my next option was to simply swap out the logic board into a new iphone and hope the device turn on problem resides in the power circuits away from the logic board.

Three questions please:

1) Has anyone seen this different behaviour based on charging option before and knows a fix ?

2) Anyone think of anything else to try before a logic board stripdown, maybe 'gas gauge' related ?

3) Is the logic board swap going to give me my data back and eliminate any faulty charging and power circuits ?

Answer this question I have this problem too

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The "gas gauge" is the chip on the battery that tracks the state of charge of the battery; this is more accurate than measuring the voltage and trying to guess how much power is left. It's an integral part of the battery; there is no way to replace it without replacing the battery.

The gas gauge connects to the main board via a "Single Wire Interface" (SWI), which carries data between the gas gauge and the main board in both directions.

"gas gauge SWI line low" means that third pin (the one in the middle on the battery connector) is shorted to ground, and therefore the phone can't accurately read its state (which is why the battery went to 0 on your call). The gas gauge chip is probably faulty.

Take the device apart, disconnect the battery, look for anything that could be shorting it, then reassemble it. If that doesn't fix it, then try replacing the battery.

iPhone 4 Replacement Battery Image


iPhone 4 Replacement Battery


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I am experiencing almost identical behavior on my iPhone 4, down to the iRecovery signature. I'm curious to hear how your repair went. Did you isolate the problem? Any ideas what caused the "gas gauge SWI line low: issuing reset" fault that you observed in iRecovery?


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I'm grateful to report that Bushing's solution was spot on. I found corrosion under our battery lead / SWI that I scraped with a jeweler's flat-head screwdriver and cleaned with rubbing alcohol. I ended up ordering and installing a replacement battery due to the faulty gas gauge chip, after which our iPhone turned on for the first time in weeks.


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but my 3gs for same problem i fixed it.. trying change battery and using custom fw restore shsh blobs with itunes and using first ireb.

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guy will be eternally grateful.
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