You could try to mirror the screen to determine if it is a display problem or perhaps a systemboard problem, before you open up the phone.
If the mirrored image is OK then more than likely it is a display problem or display connection problem, although it still could be a systemboard problem but this is less likely.
The phone will need to be opened and the display flex cable connection to the systemboard checked to ensure that it is a secure. If it appears to be OK then the display will have to be temporarily replaced and the phone checked to see if it is now OK.
Here’s a teardown video that may be of some help.
Replacement displays are available online. Just search for Galaxy J5 2015 LCD Digitizer Display Replacement to get results for suppliers.
Был ли этот ответ полезен?