Long screw damage can be caused on many different devices such as the iPhone 5S, iPhone SE, iPhone 6/6S and 7 series. Each model has different locations for possible long screw damage. Depending on the model of the iPhone long screw damage can range in severity from "basic" problems such as no backlight, no service or much bigger problems such as no image, or no boot caused by a 1v8 short.

Testing for Tristar charging issues

In order to determine if the Tristar IC is functioning properly, test the voltage of the battery terminal--after you confirm that the phone is pulling amps using the ammeter

iPhone 6S Backlight Repair

Typically for a backlight to go out on the iPhone 6S would be a result of a few things, 1 being liquid damage on the motherboard causing corrosion and shorting out the backlight circuit which contains a diode, a backlight ic (U4020) as well as few other discrete components. Another way a backlight circuit can go out is also by installing a replacement screen and bridging a few of the connectors on the LCD FPC connection thus causing a short and ruining the circuit.