I disassembled my fairphone 3 many times and cleaned it each time, tried all the tricks described in this post, but lately nothing helped. Then with the phone turned on I strongly tightened the screws that secure the connection between display and core module, it got worse… that made me think that maybe the problem is the opposite way around, maybe the pad contacts are too close to the ball spring-contacts? So I decided to unassemble it again, and this time I assembled it without the screws that secure the connection between display and core module, and guess, it worked! For now I’m happy, but if that is not enough I will try to add two small (0.1-0.2mm thickness) washers to distance pads and ball contacts further.
