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6 plus touch ic nightmare
i have done many touch ics tristars and ever audio ics but this time i reached to a dead end so i will need your experience.
i have two 6 pluses touch ics done with the jumper and the reballing of the chip. i gave them to the customers and the next day came back with no touch at all! i tried another chip and even another broadcom chip, changed screen, redone the jumper, tested the fpc connector for desoldered pins. the symptom was always the same : it worked perfectly for half day and then stoped working. no touch at all! i then changed my stencil because i noticed the balls where a little bit small, i managed to make bigger balls with another stncil, and then it lasted for a day. the next day the same symptom. no touch! if i unplug the battery and then plug it back again it will have touch for a while and then nothing. i also noticed today that if i apply pressure on the fpcs the touch comes back but not always. i suspect a loose fpc connector due to the million attempts i made to fix it but there is no visual sign and it looks pristine.
i really need your experience here.
it seems that with some permanent pressure on the shield of the screen connectors it works perfectly. i put a cpu thermal pad and i applied pressure with the screen when i closed it...iam 100% sure that all the solder balls and the jumper are making contact with the board. but out of curiosity, what can cause this?
Long screw damage on the lower left screwhole can cause this. Just measure the tenth pin on the lcd connector in diode mode. It should read around .46V. I suspect that you are probably getting .46V with pressure applied, but something different when no pressure is applied. The hifa_bysnc line (M1) goes from the 10th pin of the lcd connector to the cpu and then splits off to the backside of the board to Meson. This line is required for touch.
BTW, there is no one pin on the digitizer connector that will cause complete no touch on the screen, so you don't need to check that next time. If you have a bad pin on the connector, then you'll get a dead line at worst, but not complete no touch.