iPhone SE dead, no short found

Question

iPhone SE

6s와 유사한 하드웨어 사양의 4-inch iPhone은 2016년 3월에 출시되었습니다. 16/64GB 저장 옵션 및 은색, 스페이스 그레이, 금색 또는 로즈 골드로 제공됩니다. 모델 A1662 및 A1723.

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phonestore.uk @phonestoreuk

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iPhone SE dead, no short found

Hi guys, I have a iPhone SE here. It’s water damaged, totally dead. When connecting to power supply, before pressing the power button, the phone immediately got about 50ma of power. After pressed the power button, nothing happened, the power stayed at 50ma. It looks like something is wrong in the PMU or the circuits around it. I checked through the board, no short found. I checked the caps around PMU, I found the resistance value of the PP_VCC_Main line is a bit too small (about 170 ohm), but is far from being shorted, using freeze spray doesn’t help in such case. I injected 4.5V into PP_VCC_main, didn’t find anything unusual. The board is cold even with 4.5V of power into vcc_main line. I didn’t feel any warm anywhere. Apart from VCC_Main line, the resistances of the output lines of the PMU look ok.

I don’t know where to check next. Any idea would be appreciated. Thanks.

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Minho @refectio

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게시일: 2019년 3월 29일

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Sometimes water damaged phones do this…they are just stuck very early on in the boot process, draw little to no current and the device is just dead with no heat signatures. Those are tough to troubleshoot. You could try reballing IC’s in the area with the most liquid damage, try replacing Tristar etc. I would also look at I2C readings.

You really should start using diode mode readings as that is what pretty much the entire repair community is using , they’re much faster and it makes “comparing” values more straightforward (i.e. ZXW, WuJinXi, other techs). I will revert to standard resistance measurements when I have a doubt about a diode mode reading (i.e. super low readings).

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Hi Minho, thanks. I have one quick question here. What’s the difference between diode mode measurement and standard resistance measurement? True, I know we can compare the resistance values between a bad board and a good board (or ZXW, etc.) by using diode mode, but the standard resistance measurement does the same thing, isn’t it? E.g., a diode mode readings on a particular pin between a good and a bad board are: 0.456 vs. 0.245, standard resistance measurements are 456 vs 245. So what’s the difference?

phonestore.uk 의 2019년 3월 29일

Diode mode readings are voltage based and they are determined much faster than resistance measurements, which must be calculated. They're also a bit easier to interpret because the range of the readings is more condensed, for example typically in the 0.200V range to 0.500V range, with a few notable exceptions. They are also fairly repeatable because you are looking at an active circuit (ESD Diodes on IC inputs or any active circuitry - transistors, MOSFET's IC's...s) and not a passive resistor so it's quick and easy to compare the values you measure with similar boards or other people's readings.

If you measure in resistance mode, you will not see analogous results as you suggest in your comment but more something like 17K Ohms, or 857 Ohms or 227K Ohms etc.

While valid in their own right, you can't really cross-reference them to anything unless you have been taking notes yourself.

Minho 의 2019년 3월 29일

Thanks for your detailed explanation. By standard resistance measurement which I mentioned in my comment earlier I actually meant the continuity mode, and that’s what I usually use whenever I need to measure resistance. I uploaded two photos above. The 1st one is using diode mode, the 2nd one is using continuity mode. As you can see, the readings are quite similar. So is it safe to say they are the same? The readings in continuity mode are already times by 1000, so they are just the same as those in ZXW.

phonestore.uk 의 2019년 3월 29일

Continuity Mode is resistance, it's just that the meter will beep if it is below a certain threshold (usually ~200 Ohms). What you are seeing in your second picture is 253 Ohms. What you see in the first picture is a 0.261V. This could be just a coincidence but if you are consistently seeing similar values, then the meter is supplying ~1mA for the measurements. Ohms Law is such that you can't have voltage and resistance giving the same numerical value without it.

Most meters will supply a constant current of ~2mA with a max of ~3V to do diode measurements.

Minho 의 2019년 3월 29일

Many thanks. I am much clearer now. Diode mode is actually measuring the voltage drop, not ohms. The reason why I was confused is because it doesn’t matter what I test, be it a capacitor, a pin, a resistor, or a coil, the readings from a diode mode and conduit mode are always pretty much the same, sometimes identical. That’s why I thought they are the same. People say diode mode measurement is faster than resistance mode, but in my case they are pretty much the same. Continuity mode takes less than 1 second to get the resistance value.

phonestore.uk 의 2019년 3월 29일

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Hi Minho, thanks. I have one quick question here. What’s the difference between diode mode measurement and standard resistance measurement? True, I know we can compare the resistance values between a bad board and a good board (or ZXW, etc.) by using diode mode, but the standard resistance measurement does the same thing, isn’t it? E.g., a diode mode readings on a particular pin between a good and a bad board are: 0.456 vs. 0.245, standard resistance measurements are 456 vs 245. So what’s the difference? — phonestore.uk
Diode mode readings are voltage based and they are determined much faster than resistance measurements, which must be calculated. They're also a bit easier to interpret because the range of the readings is more condensed, for example typically in the 0.200V range to 0.500V range, with a few notable exceptions. They are also fairly repeatable because you are looking at an active circuit (ESD Diodes on IC inputs or any active circuitry - transistors, MOSFET's IC's...s) and not a passive resistor so it's quick and easy to compare the values you measure with similar boards or other people's readings.

If you measure in resistance mode, you will not see analogous results as you suggest in your comment but more something like 17K Ohms, or 857 Ohms or 227K Ohms etc.

While valid in their own right, you can't really cross-reference them to anything unless you have been taking notes yourself. — Minho
Thanks for your detailed explanation. By standard resistance measurement which I mentioned in my comment earlier I actually meant the continuity mode, and that’s what I usually use whenever I need to measure resistance. I uploaded two photos above. The 1st one is using diode mode, the 2nd one is using continuity mode. As you can see, the readings are quite similar. So is it safe to say they are the same? The readings in continuity mode are already times by 1000, so they are just the same as those in ZXW. — phonestore.uk
Continuity Mode is resistance, it's just that the meter will beep if it is below a certain threshold (usually ~200 Ohms). What you are seeing in your second picture is 253 Ohms. What you see in the first picture is a 0.261V. This could be just a coincidence but if you are consistently seeing similar values, then the meter is supplying ~1mA for the measurements. Ohms Law is such that you can't have voltage and resistance giving the same numerical value without it.

Most meters will supply a constant current of ~2mA with a max of ~3V to do diode measurements. — Minho
Many thanks. I am much clearer now. Diode mode is actually measuring the voltage drop, not ohms. The reason why I was confused is because it doesn’t matter what I test, be it a capacitor, a pin, a resistor, or a coil, the readings from a diode mode and conduit mode are always pretty much the same, sometimes identical. That’s why I thought they are the same. People say diode mode measurement is faster than resistance mode, but in my case they are pretty much the same. Continuity mode takes less than 1 second to get the resistance value. — phonestore.uk