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No Backlight and Bootloop

Hello Community,

I’ve got a question and I hope somebody can help me.

I changed the Lightning Connector and Battery on my IPhone 8 and now the Phone doesn't turn on again.

I can see the apple appear in a dark screen with no backlight but it seems to hang in a loop because it disappears and comes on again and so on.

What could be the mistake there? It's not the first repair on an IPhone and I made everything exactly like mentioned in the repair guide. I checked the connectors visually and could not find any damage.

Thank you for your help in advance!

BR

Edit: The phone itself seems to be alive, because today the alarm went of, I can set it to snooze mode and I can charge my Phone via the wallplug.

I measured the voltages and resistance now. If I get the schematics of the J5700 Connector right, the 6 Pins from 37-47 are for the Backlight? These are the Values I got with my Fluke 179 in Beep Mode:

37 - 502 Ohm, 39 - Overload, 41 - 398 Omh, 43 - 612 Ohm, 45 - 523 Ohm, 47 - 612 Ohm.

I also checked the Voltages with the Battery attached and the values where:

37- 0V, 39 - 0V, 41 - 0V, 43 - 0V, 45 ~2.6V, 47 - 0V

So could anybody help me where I would have to look for the Problem further? I guess 39 should normally have a Voltage reading too? Or would it be a better Idea to go to a repair shop with the half disassembled Phone and let them do the further work?

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No backlight and boot looping will be separate problems. For your backlight problem assuming it was working before the repair I would first rule out the screen and make sure none of the pins in the logic board connector have been pushed into the plastic. As the backlight components are on the other side of the board I doubt they have become faulty unless you connected the screen while the battery was connected. There are three pins for the backlight on the connector. You can also check them with a multimeter to check for a short or open line.

The boot looping will probably be caused by the battery or the connector, again make sure the pins on the battery connector are not pushed into the plastic. You can also put some pressure on the connector and see if it boots. You will also need to rule out a faulty battery.

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Hello Chris,

thank you for your fast answer.

Can you tell me, where I will have to check the 3 Pins with the multimeter? Against which contact? Or do I check them all against ground (=phone case?) - And the other problem would be, how I can fix this problem by myself, if I find one?

Or would it be better, if I take the phone to a repair shop to do the repair, after I found the problem? - I think you would need to know how to solder this tiny smd compontents, to fix the problem adequately?

Thank you for your help in advance!

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@LindnerG You can put your multimeter on diode mode with red probe on ground (best to put it on the end of the connector coloured in grey) If you took it to a repair shop the first thing they will do is rule out parts by trying a known good battery and screen, only than would they start looking at the board.

If it is a board problem you will need the equipment and experience in microsoldering to do the repair.

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