iPhone 8 Plus touch not working

[Mohammed]

Hello guys! I have an iPhone 8 Plus without working touch function.

History:
Shop received it with a broken screen. Customer didn't want to fix at Apple because she needed it back fast. After screen replacement the tech found out that he used an i7+ screen because the screen didn't close well, but touch was still working. After putting on a i8+ screen touch function failed, so he put the i7+ and original broken i8+ screen back and neither would make touch work again.

Visual exam:
No long screw damage, no missing or loose components, no other physical damage, no water damage. The only thing I could find is that they tried to clean the inside of the connector with something sharp. They confirmed that they tried to clean the connector out with a tweezer.

What I tried:
- tried my own known good i7+ screen as I don't have it for the i8+....didn't work, I'm not sure if touch will work at all with an i7+ screen
- updated software
- compared schematics of the touch/display connector between the i7+ and i8+ and they are exactly the same. So took diode mode measurement with the i7+ as reference and didn't notice anything significant
- checked the connector again very close and cleaned it with alcohol...nothing

What I think:
- I have no experience with the result of placing an i7+ screen on an i8+, maybe that's a NO-GO. But wiring for the connector are exactly the same
- I think I will try with Apple see if the will do an out of warranty screen repair
- Anyone with experience in replacing i8+ screen (I dont do screen repairs) seen this issue?

[eDigitCom]

I would say not much iPhone 8 plus coming in for repair at this stage due to them been under warranty?? I not seen any. IPhone 7's OK

[crea2k]

I'd check voltages, as although the touch ics are on the screen there are still touch descrete components. So we know the touch ics on the screen are most probably good if you've tried several screens so what tells those touch ics to turn on or what tells the phone there is a screen connected to the digitizer socket. I'd probably look there. It might lead you back to the pmic or cpu but it's worth checking if there is some ic in between that's not being told to turn on. (These are just theories, I don't have a schemetic handy£

[Jessa_the_Professa]

I believe that I had heard a few reports that some (maybe all?) of the 7plus screens would show image but not have touch--It may be that the touch drivers in the screen are not compatible, like the 6s copy screen ics were not compatible after ios11 for awhile.

[Mohammed]

Ok, so I ordered a new screen for the i8+, not working. Then I started to measure the 2 power line for touch: pp1v8_touch and pp5v1_touch_vddh. Both were missing so I applied voltage to both of them, but still no working touch. Im gonna abonden this one

[crea2k]

Where do they come from the pmic ?, are those voltages present anywhere else on the board ?. I'm just wondering if some lines have been blown out because of using the wrong screen.
Iv had a wifi ic on an iPad and phone before with missing 1.8 line, I just jumped it from where it came out of the pmic and worked fine then.