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No touch function after backlight repair (Advanced!)

Hi, this is my first question here.

I own a repair shop and do repairs on iPhone's for at last 3 years.

Now i got a iPhone 6s that drives me CRAZY!!!

A customer brought it in for a backlight damage, as always i checked the FL4211 for damage, none to bee seen also no burning, after i took of the CPU shield and the D4021 was a bit raised so i replaced it, after that the backlight came on and worked like a charm.

BUT, after the initial boot, the image on the screen was full of a pattern i have seen before, namely when you turn on a iPhone 6/6plus without the U2402 on. Vertical lines with some kind of checkered pattern.

I replaced 3 screens, cleaned the FPC, restored with latest os, nothing changed.

After i measured the "PP1V8_TOUCH_CONN" and here i found a open circuit, i made a strap on the "FL4209" and after that everything was in order with that line.

Still no touch function, i measured the following lines:


All of them give me a ~0.420V voltage drop to ground, no open circuit on any of them!

Also i mesured the "PP5V1_TOUCH_VDDH" when the phone was on and i got the 5.1V on that line.

I cannot understand what the problem is? Where am i missing something? There is no mechanical damage to the board, all SMD parts are in the right places.

Maybe someone has a ideea...

Thanks in advance.


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Have you checked the Chestnut circuit? Beyond the 5V1 line, there is also the PP5V7_MESON_AVDDH

& PN5V7_LCM_MESON_AVDDN. There is also the PP1V8_TOUCH (Fl4209) line which also powers the touch functionality.

I would also check the AP_TO_TOUCH_RESET_L line (FL4134). Then there is the LCM_TO_OWL_BSYNC line (FL4230). There are lot's of Touch lines on page 42 of the schematic.

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I have done some iPhone board work but I still don't know much but I know what if you search up STS telecom on Youtube he does lots of these problems. It's worth having a look.

Hope that helped

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Thank you but still did not find a solution to my problem...


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in my case i checked SPI_TOUCH_TO_AP_MISO and no value checked on another working board and there is a testpoint next to the cpu i could run a jumper from but my bord dont have value on the testpoint either so the last point is inside CPU so am stuck at this point

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In my case in diode mode I get 0.001v = short to ground? I would reball CPU but it feels the CPU is shorted internally?


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