It would be nice that it was so simple to fix but I highly doubt it’s the issue. Reasons why I don’t think it has anything to do with the connector:
- It’s a digital signal from a controller chip on the display for the LCD integrated in-cell touchscreen. I don’t see how the connector could create such an issue.
- No issues with display and that is likely the majority of pins on the connector. Any physical connector issue would be bad news.
- I was unable to reproduce the issue by applying more or less pressure to the connector while the phone was on during several different investigation attempts.
- The foam is there to stop the connector from disconnecting inside the phone not as a requirement for good connection.
Here are the FP4 schematics: https://www.fairphone.com/wp-content/uploads/2022/09/FP4_Information-for-repairers-and-recyclers.pdf
Page 53 for display connector. It has 3 pins for touch signalling as well as many pins for backlight and display (MIPI). So if the physical connector had issues we’d be having way more issues than just the touchscreen. The issue has got to be in the LCD itself, the LCD driver IC which includes touch support (HX3112) or in-between.
My hunch is that it has something to do with the camera cutout and the processing of the touch signals on the HX83112.