[link|https://www.ifixit.com/User/4246223/Ulrich+Elikana|Ulrich Elikana|new_window=true] the only way to check on that flex issue would be by checking the connector and the cable (properly seated, tears etc.) itself first. After that you could try a new touchscreen which will have a new flex cable. If that does not resolve it, the issue could come from the IC on the circuit board. That would require some boardlevel repair knowledge, schematics and component placement chart etc.