iPhone 6 is dead after replacing touch IC
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.
Is this a good question?