Chosen Solution
Hi everyone, I run a phone repair business for a few years. Yesterday a customer brought me an iPhone 6 with touch decease (touch is completely dead). I removed and reballed the silver touch IC (U2401), put it back, the touch was back to life. However one line on screen was not responsive. The touch was working on every corner except one line not responding. So I thought the silver touch ic was probably not properly reballed. So I removed it and did the job one more time. This time however, the phone was completely dead. I removed the silver touch ic again to verify there is no short on the chip. I tested the phone again without the silver IC, still dead. I tested the battery line, didn’t find any problem. Voltage is normal. No short on the vcc_main line either. Finally I removed the black touch ic (U2402) to verify there is no short on the black touch ic. I tested the phone without U2402, unfortunately the phone is till dead. I want to ask, can the phone turn on without the black touch ic (U2402)? I googled it around, someone said the phone can turn on without that chip, someone said it must be there in order for the phone to turn on. So I am a bit confused now. Can anyone confirm that if the U2402 is a must to turn on the phone? Also can anyone shed light on what to do next? I don’t think the CPU is over cooked, I only used low temperature. Many thanks.
The current best practice for Touch Disease (at least on the 6P) is to replace only the Meson IC and place a jumper to secure a weak line on M1. Techs have found that Cumulus is rarely the problem. For the iPhone 6, the M1 pad does not have a poorly designed trace but it is connected to a via. I would certainly inspect that very closely next time you do a Touch Disease repair. As for this particular phone, it’s hard to say. Once you get into multiple attempts on the Touch IC’s, all bets are off. Even if you are careful with the heat flow, the fact that you have done it so many times increases the risk of secondary failure. We’ve all been there. So I would go back and focus on these possibilities and hopefully find something: Inspect with a microscope all of the surrounding passives. You may have a solder bridge between components, a lifted pad or partially dislodged component, tiny solder balls that exploded out from surrounding IC’s that got overheated. Also look very carefully on the reverse side of the board. The CPU is almost directly opposite and held in place with underfill. That’s where exploded solder balls happen the most.Another common issue is the rows of passive on the flip side next to the screen assembly connectors. With excessive heat, they are sometimes sucked up by the epoxy securing them and they now fail to make proper contact with the pads. You will typically see camera problems when this happens but who knows…it’s worth a try.Go back and check all of the main voltage rails created by the PMIC (PP_CPU, PP_GPU, PP1V8 etc).Try to do as much as possible before attempting to re-do Cumulus or Meson. Report back and let’s see where we go from there.
I know this is an old post, but just for the record, i had the same problem after replacing touch ic. the culprit was under the wifi/bluetooth module, ppvccmain joined with ground under the chip, i had to remove the wif module, reball and put it back on, phone turned on after that, but what a job.
