Chosen Solution
Hi guys, I have an iPhone 6 Plus here. It’s quite strange. The touch works, but not fully working. In particular, one line on the screen is not responsive, which means when moving Assistive Touch icon around the screen, it won’t pass that area. Tried a few known working screens, made no difference, that particular area is not responsive. Due to the notorious touch disease on 6 plus, I thought it’s the touch IC problem, so I went ahead to replace two Touch ICs (Cumulus and Meson chips), and as routine I also did the M1 jumper. To my surprise, it made no difference either, the problem is exactly the same as before. I also tested the resistance value on every pin of the touch connector, it seems the resistance are all ok. The phone is not water damaged, no damage or corrosions on the touch FPC connector. I don’t know where to go next. Any suggestions would be appreciated. Thanks.
That’s an interesting problem indeed. A known-good screen, M1 jumper, new IC’s, proper readings on the connector and yet the exact same dead spot. I would surmise the issue is with the pins that allow the two IC’s to communicate to each other. That’s the only part of the circuit you have checked. Meson has a series of 24 pins labeled: SAGE_TO_TOUCH_VSTM_OUT and a series of 15 pins labeled TOUCH_TO_SAGE_SENSE_IN. They are driving the X-Y grid of capacitive touch sensing elements of the digitizer. Essentially, they track your touch, multi-touch and gestures. When you touch the panel, Meson does some magic and sends the raw data out to Cumulus via the SAGE_TO_CUMULUS_IN lines. These are the lines you have not checked and they are interconnected with the “trailer park” capacitors between the two IC’s. I would start by checking if those caps are dislodged and then test them to insure they are good (not shorted). In a worse case scenario, an inner trace could be damaged so that would require that you probe the pads directly underneath the IC’s.
