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Versión GSM de la cuarta generación de iPad lanzada el 2 de noviembre de 2012. Número de modelo A1459 / 16, 32 o 64 GB

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Ipad 4 Irregular Voltages and 0 amp draw

Hi, any suggestion is highly appreciated because I'm in a state of depression rn thankyou :D.

Disclaimer, I usually do a laptop repairs so mobile repair is not my specialty, sorry if my approach you found somewhat dumb.

the ipad comes with no display problem with 0 amp current draw, upon checking i found the voltages around the board (when the power button is pressed) is pulsing like 3v and goes back to 0v and so on.

this symptom is look like the ipad itself is trying to boot but failed, then i began to search if there is a short circuit across the board, alas there is no short at all and all voltages look like present and healthy except for the pulsing issue.

*the pulsing issue persists when the ipad is only powered by the battery. (with and without the power cable attached)

because i have no idea where to start diagnose further, i read in many forums that U2 tristar is likely to be the culprit, with that idea I tried to replace the tristar with a new one and the problem is of course still persist.

what i have already checked are

  • the battery is known good
  • charging port no problem (tried another one)

* no short circuit

  • power button is good i think (i've tried jumper it from the on off from the power button connector and the problem still the same)

i think the real culprit will be U8100 which is the PMU because the PMU is responsible for power delivery to those component on the logicboard (right?) but im not sure because i don't have enough evidence yet to replace that PMU

or maybe the communications board (where the baseband chip located i suppose) can cause the issue?

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How do you know the battery is good? First thing I'd try is a new battery. If it's already had one I'd remove the motherboard and check for pin damage on the battery connector. Pin damage can cause problems with the board not understanding the battery levels etc.

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@strongbow i've tried with another known good battery (taken from a working ipad) and the problem still persist, the pin looks good, by the way the voltage coming from battery is stable and healthy (only the standby voltage before power button is pressed), but just when the power button is pressed the voltage become pulsing like that so from that thought process i think the battery will not be causing the issue. thankyou for your respond do you perhaps have another idea?

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@zidnyyasrah I'd still be inclined to try a new battery as its a 11 year old ipad now. More so if it still has the apple battery fitted. Might be showing good voltage but might lack the amperage to power it.

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@strongbow make sense, but actually yesterday i've brought a new battery out of curiosity and unfortunately the problem still persist,

also i've been injecting some voltage from the battery connector before, and the amperage is not increasing at all, the logic board didn't take any ampere.

beside the ipad is 11 year old, the customer said that he really need his data in this ipad its like super important company data or something idk. that is why i really want to fix this thing,

do you have any other idea in mind that i can try?

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Have you tried something as simple as a hard reset with the charger connected? Sounds simple but you can only try. Press and hold both power and home buttons for 20 to 30 seconds and see if the apple logo appears.

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hello Zidny,

that repeats, it may indicate damage due to incorrect polarity when trying to repair. As you know, integrated circuits do not tolerate improper voltages, especially negative ones. The damage is not repairable, the power supply must be replaced. Details can be found in the schematic diagram. The method of diagnostic of power IC you know I'm sure will acurate. In another case, when the pulsation of a different shape and waveform (details can be found on your oscilloscope) may indicate damage to the logic of the motherboard. Usually it will a capacitor or resistor that has already made its life. You will need a multimeter and a schematic diagram. The repair looks identical to the laptop, but here everything is 10x smaller :-)

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thankyou so much for your response,

when the ipad comes to me, it looks like haven't been touched yet. and my first attempt is try to charge it with the known good original charger., then i remove the battery and check the voltage coming from the battery connector in the logicboard, and the voltage is already pulsing like that.

I've seen the schematic of this model, by the power supply IC did you mean the U2 Tristar? or the PMIC? (U8100 for this particular model on the schematic) and for the capacitor, I've checked all of them and there is no short circuit at all, as for the resistor, i haven't gone through that yet.

From my understanding, (Please do correct me if I'm wrong) PMIC is responsible for giving the right amount of voltage across the components in the logicboard, then isn't the PMIC is the biggest suspect right now?

should i just replace the PMIC?, or do i need to measure all of those resistor first? or do you have any other idea in mind?

thankyou so much for your time and effort.

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and yess im having a hard time checking those super small and extra tight components :D

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yes, the D2018, mounted in the u8100 place is an MPMU and is responsible for generating all main power lines and the CPU core. Check the schematic, but before that you have a switching transistor. It's worth taking a look at that.

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@tojaert right, I found there is two mosfets before the D2018, ill check them both, and after that will do change the MPMU, I'll let you know how it goes later. and again thankyou so much for your suggestion

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Zidny Yasrah estará eternamente agradecido.
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