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iPhone 7 no power. pp1v8_sdram and pp1v1_sdram shorted

Hi gyus,

today I was working on Iphone 7. No power what so ever, does not react to a charger (0 current being drown).

Plugged in to DC power supply, phone does not react to power button at all (not shorts, no reaction on power supply). However the device reacts to a lightining cable. Current goes to .010 amps and down to 0, back to 0.01, down to 0 and stays in that loop until power disconnected.

When doing diode mode checks on logic board, started from bottom flex cable socket and found 2 shorted lines:

pp1v8_sdram

pp1v1_sdram

I have injected 1.8V 1A directly to both of them, the only part that was getting warm was a CPU.

Am I right the faulty part on my board is CPU RAM?

Is it even worth trying to repair it?

I’m pretty convenient all the tests I did eliminated other components from a “fault list”.

Just wanted to confirm it with more experienced people, since my own experience in that matter is very limited, I just started my repair adventure about a month ago, learning everything from the internet :)

Sorry for not the best English and Thank you :)

Marcin

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·         What is the history of the phone?

·         Have you ruled out parts?

·         Has it had prior repair attempt?

In my experience an 1V8 sd ram short would draw a constant 600 to 700mA. When testing with a DC power supply you should prompt it to boot by inserting the charger cable for three seconds than remove it. Use a proper squid not one of those red ones that has a button on it for prompt to boot.

Just because something gets warm it doesn’t mean it is shorted. If in any case you were correct in your findings and the ram has multiple shorts it is a very difficult repair, it is easier than the 6 but the ram can still warp while removing and there is nothing to say you won’t have damaged pads on top of the CPU.

If you want you can supply us with the diode reading of C1874 and C1823 remember red probe on ground.

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Hi,

I do not know the history of the device, I did rule out all parts (used known good housing and screen), checked what IC’s are on those 2 lines, and only 2 components are PMIC and RAM.

Visual board inspection tells me there were no prior repair attempts.

In my 1st post I wasn’t clear enough, I was trying to prompt it to boot by inserting the charger cable , DCPS shows 0.01 amps jumping down to 0, back to 0.01 and looping for as long as powered.

(I also tried it in known good housing with the same results)

diode reading of C1874 is 003 and C1823 is 008.

Any other ideas?

Cheers :)

par

@blaszek When you are inserting the charging cable you are taking it out in around 3 seconds? I would concentrate on the 1V8 line first. There are numerous IC’s that use this line besides the ones you mentioned. Starting at the most likely ones presuming it is not the CPU would be U3101, U4001, Baseband PMU, Baseband CPU, Wi-Fi IC, U3601, U3701, U4806, U4802, U4805. There are probably more. Remember the more components you remove and replace the more variables you will have.

If you manage to trace it to the CPU just wait until you get more experience before trying to remove the RAM.

par

Actually by mistake I was not telling you the right readings I was getting on my DCPS.

The moment I plug in charging cable current goes to 0.01amps then back to 0, over and over again. After 3 seconds when I unplug it current goes back to 0 and stays still. Phone is not drawing any power.

EDIT.

Finally managed to get a reaction from the board when trying to prompt to boot using charge cable. Unfortunately for me not a happy ending i guess

Current goes up to 0.750 amps and moving around up to 0.8

Two parts are getting warm, u2101 and CPU RAM.

I guess I need to practice a bit on dead boards and take my chance in replacing RAM :)

par

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Sure freind, I got you, I also have same experience 1.8v short on iPhone7 plus, it requires to replace the ram, but you have to be cpu experts before you replace the ram.

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Marcin sera éternellement reconnaissant.
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