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:

• "SPI_AP_TO_TOUCH_CS_L";
• "SPI_AP_TO_TOUCH_SCLK";
• "SPI_AP_TO_TOUCH_MOSI";
• "SPI_TOUCH_TO_AP_MISO";
• "TOUCH_TO_AP_INT_L";
• "AP_TO_TOUCH_CLK32K_RESET_L".

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.

D.