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2015年9月25日にAppleから発売されたiPhone 6Sの修理情報とガイドです。モデル A1688、A1633。

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All power rails power up and down?

Just changed a backlight driver IC on a water damaged iphone 6s.

It was booting and showed image, just no backlight before that. before i changed the backlight driver ic i changed the diodes as well, also checked all other backlight components for issues. the driver IC was the last thing i changed before this happened.

Even removal of it wasn’t changing this new issue back.

I cannot find a short anywhere on all those other rails. Checked all for short and measured the voltage all go up to what they should have and power down again and repeat.

If i short such a line it immediately goes into shutoff and i need to prompt it again.

So i am thinking it is a IC with an issue but which one ?

Does a broken PMIC such things ?

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Check the voltage (and diode mode) on the PMU_TO_SYSTEM_COLD_RESET_L line. This is the reset signal going from the PMIC to CPU. You should also check the other PMIC RESET lines (those that are probe-able) and the I2C lines to see if anything else is out of line. Something is causing the PMIC to shutdown and reset the CPU yet once it turns off, the power applied makes it restart and the cycle continues.

The problem here with these “oscillating” states is that it is a circular problem and because you have a water damaged phone, all bets are off. It is possible that when you applied heat to repair the backlight circuit that something went wrong but it is also possible that this could just be a lingering effect of the water and would have happened sooner or later.

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@refectio Minho thanks for all the support you give to people here. I found this article by searching for PMU_TO_SYSTEM_COLD_RESET_L . I recently bought a cheap USB Oscillopscope and Logic Analyser which I used to confirm that this line was toggling. See image, as you can see the line is only up for 50ms before going low again (reset is low) so hard to find with a multi meter. I would encourage all repairers to look at this device as it also decodes I2C and SPI.

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Like Oliver all of my PMU lines were not shorted but as soon as the line goes low there’s no PP1V8 so no I2C etc., On DC power I saw the phone going from 0 mA to 3mA very quickly. Your post led me to look at reset lines and although I cannot get to these I thought the most likely was the TRISTAR_TO_PMU_HOST_RESET so I changed Tristar and boom …. all fixed… Thanks once once you’re a *

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That's awesome Nathan, glad I could help. I don't think that Tristar is a universal solution to this RESET issue but it's great when it works!!

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Oliver Berger さん、ありがとうございました！
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