Chosen Solution
I have bought a broken iphone 6 from eBay to learn micro soldering and repairs. It is all going well but this device came to me and has been worked on before. Many of the capacitors have been ripped off the board, mainly on VCC_MAIN. I found the main fault which was a shorted PP1V8_SDRAM, the short was caused by a faulty PMIC which has been replaced. When connected to a bench PSU the phone at power on draws around 45mA and does not boot. I have checked the following and they’re all OK. VCC_MAIN PP_CPU 0.775V-1.0V PP_VAR_SOC 0.9V-0.95V PP_GPU 0.9V-0.95V PP1V8_SDRAM 1.8V CPU PP1V2_SDRAM 1.2V CPU PP0V95_FIXED_SOC 0.95V CPU PP1V8 1.8V CPU PP1V2 1.2V PP1V8_GRAPE 1.8V RESET_1V8_L PP3V3-USB——A8 CPU PP1V8_VA_L9_L67——U0900、U1601 PP3V0_TRISTAR——U1700 USB PP3V0_IMU——U1901 PP3V0_NAND——U0604 PP3V0_PROX_ALS——J111 PP1V0——A8 CPU PP3V0_PROX_IRLED——J111 PP1V8_ALWAYS——A8 CPU PP3V0_MESA——U2100 Does anyone else have any ideas? Not sure what the next signal should be to the CPU to boot? I think it may be a dead or broken CPU :-( Do I need to replace all of the missing CAPs…. no long screw damage either…..everything else looks good. Any help very much appreciated for someone learning…. loving the challenging though…..
You should also check the outputs from the baseband PMU (U_PMICRF). If something is wrong there, the phone will not boot. If too many caps are missing on VCC_MAIN, it could impede the boot process but there’s no clear cut-off of how many (or which ones) you need. The bypass caps filter the line from noise caused by the internal “switching” but they also act as a reservoir of “juice” when an IC has a rapid need for more current. The inherent inductance of the copper traces supplying the power actually works against a rapid supply of current. That’s why the caps are placed as close as possible to the IC’s power pins as possible. Was this phone water damaged? If it was, then you could have some issues underneath certain IC’s. If the problem is CPU related, then it’s pretty much done. Reballing a CPU is not for the faint hearted and has a low success rate. Take this opportunity to learn your way around the schematic and try again on another phone. What you learn there may eventually help you find a solution for this one.
