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DEAD, no respons, No power to the battery, possible the U2 ic?

I bought a dead phone, and by dead i mean REALLY dead, no respons at all! Tried all you can do by the cheep tricks, but nothing happens.

So I began to tear the phone apart, the first thing i notis is a screen replecment been done. I allso get no voltege from the battery, allso no voltage from the logic board when charger inpluged. Or a reading of 0.1 V for being exact. Theres no short circuit when put the probes on + and - I got around 700 Oms that drops down with time.

When I switch the logic board around and opened the sticker I allso notis some corrosion on one capacitor and two burn marks on the sticker indicated that two other capacitors gone HOT. So I cleaned the board with Iso. and broched it and finely heated it up with heatgun. That did not fix the problem.

One thing im encountered whas that when charger pluged in, the PMIC got REALLY hot! Could the PMIC might been gone bad? Or is it like many others with similar problems the U2 ic? What do you think?

Update (09/03/2016)

Block Image

Small capacitors hot mark. And little green corrosion. Find one small water trace when i first opened this sticker.

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I now know that the PP_VCC_MAIN is the shorted line. So its a nightmare.. the short could be anywhere! Im going for the pmic first and last resort, just because it hitting up when charging. Wish my luck..

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I checked the resistens and found out that I've got 22ohms around the PMIC and the WIFI cap, and near the Audio IC I've got don to 3ohms, if i put the probs togheter it reads 2ohms, so its defently near the U0900!

NOW! The thing i found weird, the PP_VCC_MAIN in to audio IC is defently NOT shorted?? The four caps incl C1075 shows no "beeb" and have high resistance to ground? Insteed I've got short in PP1V8_SDRAM, that line shows 12oms. The cap i belived cause the problem was c1025, that showed 3oms. But still i short!

So far I've removed C1033, C1014, C1025 and C1263, they all except C1025 looked bad. I have not replaced them.

So my next guess is the audio IC, cant find a bad cap nerby and i get low readings on nearby caps, you can allso see the burnmarka on the shield ahowing that two lines to the chip gone really hot!

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Have to add that the two lines that gone hot is the above mentioned PP1V8_SDRAM who is still shorted, but the other is either PP_VCC_MAIN or PP1V8_VA, but not shorted now.

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I think I´m going to check the C1016 cap first, thats the only cap i haven´t check yet. Just have to remove the shield-frame before doing so. I should hear a "beeb", but the question is what resistance. C1014 got 12ohm, but maybe the distance between them could cause a higher resistance.

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This is a belated answer so hopefully it can be of use to folks who search for and find this question.

First of all, a water damaged phone can be a nightmare to troubleshoot. Based on your comments, it's not entirely clear if VCC_MAIN is shorted or not. You have to take your time when probing and double check your measurements when they start becoming contradictory.

You have to start at the beginning and check PP_BATT_VCC, PP_VCC_MAIN and PP5V0_USB. I would start by checking to see if those rails are shorted to ground. If one of these rails is shorted to ground, then you will need to identify what is causing the short. It could be a bad decoupling capacitor, conductive debris or defective IC that is directly supplied by those rails.

If they are not shorted, then you can connect, preferably, a known-good battery (or a current limited DC power supply with the appropriate connector adapter) to see what voltage you measure. If the voltage is low or lower than the battery voltage (which you measured before plugging it in ;>), then there could be a short circuit on secondary subsystem that is causing the battery or DCPS to be current-limited.

If you are measuring the proper voltage, then you move onto the PMIC and check the voltage rails it generates. The PMIC generates ~15 voltage rails. They are all important (for obvious reasons) but the ones to check first are as follows:

  • PP_CPU & PP_GPU – These rails supply the CPU & GPU. They are low resistance rails so they may “beep” when you test them on your multimeter in continuity mode. It’s important to look at the reading and not focus just on the beep. You will typically measure something around 20-100 Ohms on these lines.
  • PP1V8_SDRAM & PP1V2_SDRAM – These rails supply the SDRAM (which is sandwiched with the SoC/CPU).
  • PP_VAR_SOC & PP0V95_FIXED_SOC – These rails supply the rest of the System on a Chip. What we commonly refer to as the CPU is actually a SoC.
  • PP3V0_Tristar & PP3V0_NAND – These rails supply Tristar & the NAND chip.
  • PP1V8_ALWAYS – This is an “always-on” voltage rail that is used for the bootstrapping of the device
  • PP1V0 – Supplies the High Speed Digital Communications via the SoC

The PMIC also generates, what I would consider secondary, yet still important voltage rails for the following sub-systems: PP3V0_MESA, PP1V8_VA_L19_L67, PP3V0_PROX_ALS, PP3V0_PROX_IRLED, PP3V0_IMU, PP3V3_USB and PP3V3_ACC (not important).

At some point, you have to call it a day with water damaged phones.

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