iPad A2197 no power, A10 and other IC become warm, only 0.5A charge

[proxneo]

Dear reader

TL;DR: iPad not turning on, A10 and power IC become (very) warm when attempted to turn on but this power-on cycle has a 'cooldown' period wherein powering on doesn't work, does not take more than 0.5A charge.

I am working on an iPad 7th generation 2197 from >2019 with no / limited charging and no boot issues. It is a refurbished purchase made in 2021. It appears the 'refurbish' company has either done prior motherboard work (all protective component shield layers are gone) or is one of the many trash refurbish companies (little screen adhesive left, component shields removed, incorrect cable management/placement, loose and missing screws), of which I suspect the latter.

Prior to the current no-boot scenario, it had apparently shown charging issues for a bit leading up to the current failure. It would not always take charge during this. I have no more useful information beyond that.

It has the following characteristics:

• No boot screen when turned on with power button
• Does not respond to multiple button-combo reset attempts
• Charges at 0.480A-ish for a bit, then goes to 0 with occasional 0.020A-ish spikes. I seem to remember someone on Youtube saying that he has made a connection between the 0.480A charging rate and a defective cap / passive component short
• With new battery the 0.480A-ish remains for longer, but still nothing on the screen when trying to power on
• Sometimes responds to power button, but not always. By responding I mean that the A10 chip and 343S00314-A0 power IC become very warm to the touch fairly immidiately, as well as some coils / bucks (?) such as L8113 near the power IC. This lasts for about 30-50 seconds, after which it won't respond to the power button input. It does not display anything on the screen during this

What I've done so far:

• Watched quite a few repair videos on this and similar ipad generation repairs with different faults
• Checked battery voltage, its at 3V
• Replaced battery (new one arrived with 4V state of charge)
• Resistance between battery ground pin and any non-component ground point on the PCB ground is 2 Ohms
• Tried to 'inject' operational voltage at battery connector with power supply (4.0V 0.5A), but it doesn't seen to respond to that. Perhaps because my power supply isn't very capable, as it does respond when the battery is used as a power source
• Applied IPA to detect hotspots
• Quick visual inspection of caps and other components
• Downloaded the schematics and components placement diagram

What I haven't done or can't do:

• Haven't changed screen
• Don't have tristar test tool
• Don't have thermal camera

I, as the repair person, have the following characteristics:

• No prior experience in Apple repairs, don't know what values are supposed to be or what common faults are
• Occasional basic schematics-based repair (audio, appliances), but the path line (VCC component path tracing and checking) diagnosis I haven't done yet
• Not a business, this is a 'I can take a look but no promises' handyman offer I made to the owner (whom I know personally)

Tools availabletp me: small but sufficient microscope, soldering iron, rosin flux, IPA, multimeter, USB power meter, if needed a hot air station (on loan)

Are there any suggestions where I can look and measure first, within the limitations I have (given my tools and knowledge insufficiency)? I'm not against asking or bringing it to a motherboard component repair shop, but it appears there aren't many around in my region / country. Most 'repair' shops are replace-type shops, where they replace faulty components (camera, power button, etc.).

Thank you in advance.

Kind regards,
proxneo

[proxneo]

Bump

[mon2]

Hi. This is a painful unit. Personally getting tired of cell phone style parts used in such products with respect to the required repair effort. Need a very steady hand and nice microscope to review these tiny boards. Have them but perhaps losing my patience.

when you attach the power adapter cable using the lightning port, do you observe an immediate spike to the 480mA current draw? Or does the current climb up over time?

OT: Ferry (Netflix) = amazing series. Loved the acting and cast.

[proxneo]

[..]

Apologies for the late reply, I was on holiday.

The current draw to 480mA is immediate. As is the drop down to 20 mA after a while.

[mon2]

An immediate spike of current like your case is often a shorted cap onboard. Remove all power. Meter in resistance mode. Measure the resistance to ground of each power rail. Suggest each inductor to be checked for its resistance to ground.

[proxneo]

That was my first thought as well, based on initial research on this behaviour.
Thanks, I will check these components. If I manage to identify them correctly using the diagram, that is.

[mon2]

The inductors you will need to review will be marked with a 'L' prefix = coil / inductor. Each such inductor is very likely linked to a power rail. Regardless, no harm to test each one you can probe. One meter probe on the inductor (either side) and other meter probe to ground.

Start with the battery connector (WITHOUT the battery of course). This is the positive (+) tab from the battery itself but on the logic board. What is the resistance to ground?

The schematic and boardview diagrams are posted on this forum for the A2197. A low resistance usually means a shorted component - there at least one video from Alex on this exact issue:

https://www.youtube.com/watch?v=jnYwrcKIcQ0

[proxneo]

Resistance to any random ground point, as measured from the positive battery terminal on the PCB side, is about 2.3M Ohm.

[proxneo]

The inductors you will need to review will be marked with a 'L' prefix = coil / inductor. Each such inductor is very likely linked to a power rail. Regardless, no harm to test each one you can probe. One meter probe on the inductor (either side) and other meter probe to ground.

Start with the battery connector (WITHOUT the battery of course). This is the positive (+) tab from the battery itself but on the logic board. What is the resistance to ground?

The schematic and boardview diagrams are posted on this forum for the A2197. A low resistance usually means a shorted component - there at least one video from Alex on this exact issue:

https://www.youtube.com/watch?v=jnYwrcKIcQ0

Resistance to any random ground point, as measured from the positive battery terminal on the PCB side, is about 2.3M Ohm.

I finally was able to take some time to look at this board again. A week ago, I used the "flux smoke" test for finding overheating components, as I don't have a thermal camera. I could not find anything though. Cleaned up afterwards with IPA.

Today I checked all inductors marked L. I also checked if their solderjoints may have come loose, which wasn't the case. I've found a similar post, in which measuring the caps was recommended (this topic). I borrowed martyjelen 's image, hope you don't mind, where I added values of both caps and inductors. See attached image. L prefix is inductor, C prefix is caps, the subsequent values are resistance in Ohm to ground (with indicated with M and K). Some inductors were not really reliable when measured, by that I mean that the resistance kept creeping up or down and wouldn't stabilise. Could be my meter though.

I was going along the board for the caps and inductors, but at some point I noticed that one cap was askew. I touched it gently and it came loose from its pads. Now, AFAIK, they can handle a bit of force. I was able to dislodge it with a gentle push with a needle, so I assume it wasn't attached properly / came loose / COULD be the culprit of the short-like behaviour?? I lost the tiny prick, so can't measure it...
It is cap C81E3. See attached board schematic snapshot. I assume its in parallel with 6 other similar caps, if I'm reading the schematic right (I'm not good at reading schematics yet).
Would it be safe to use the device without this one?

Thank you in advance.
Kind regards.

[mon2]

This capacitor @ C81E3 is a bulk capacitor and it will not be missed if you remove it off the PCB. The other caps are ample to filter this voltage rail. There is a concern if the slanted angle of this capacitor has shorted or was shorting to the left side leg of the inductor that is just above this capacitor.

If U8100 is heating up, then remove all power -> meter in resistance mode -> measure the resistance to ground of each power rail that is created by this component.

The reference to the ~480 mA peak current and a shorted cap was by Alex in one of his YT videos. He found a shorted cap onboard.

[proxneo]

Apologies for the long radio silence. New job etc.

This capacitor @ C81E3 is a bulk capacitor and it will not be missed if you remove it off the PCB. The other caps are ample to filter this voltage rail. There is a concern if the slanted angle of this capacitor has shorted or was shorting to the left side leg of the inductor that is just above this capacitor.

If U8100 is heating up, then remove all power -> meter in resistance mode -> measure the resistance to ground of each power rail that is created by this component.

The reference to the ~480 mA peak current and a shorted cap was by Alex in one of his YT videos. He found a shorted cap onboard.

Thank you for the information. Unfortunately, after removing the croocked cap, there is no change in boot behaviour. No Apple logo etc. But all ICs do heat up, like before. The A10 chip get very warm within seconds, the U8100 gets warm.

How can I indentify what the power rails to the U8100 are? I do not have access to boardview schematics (can't find any), only block diagrams. If I can manage using those, what and how would I have to look for? Again, this is my first repair attempt at this level, so I'll need some introductory guidance.
Thank you.