Free Microsoldering Forum – Ask an Expert
Iphone 6s Plus no boot
This Iphone 6s plus got wet , then brought to me for repair , when i opened it i found few resistors and filters were missing and some caps were loose, I mounted everything correctly then ran a test on it , phone boot up to 1.20 AMP on DCPS power supply then shut down , so i proceeded to remove and replace tristar since then all i am getting NO Image , phone would pull 0.93 Amp on DCPS then shutdown and restart again over and over again , I would love some help please.
The cause of "no boot" from water damage can be many things. What area was all the damage in? Are there any IC's around this area? What lead you to replace the Tristar? If it is drawing a large amount of power on boot, but no current draw before "Request to boot", then it would more than likely be a short past VCC_MAIN. I would usually check caps around PMIC and backlight caps. Freeze spray is your friend! Solder a wire to VCC_MAIN and inject 3.5V at 1A to 2A and check for heat using freeze spray or thermal camera. That is usually the fastest way to find a high current short. If no short is present, then move to checking data lines.
With no image, you should measure pp1v8_lcm, pp5v7, pn5v7, ap_to_lcm_reset_l in diode mode. That's your starting point. From what you described, your phone may not really be booting at all. It's hard to say.
One frequent cause of boot loop like you're describing is when the CPU gets too hot and reboots. If that's the case, then you can try freeze spraying the cpu upon bootup to see if that helps.
I changed tristar because of the behaviour of the very first time when i saw it was booting and restarting , When i measured Values on PP_CPU is out of range ( way to high when comparing to a known good board and PP_GPU is way too low comparing to known good Board , the impact that i saw was mostly suffered around the lcd connector , but someone had worked on the phone before it got to me , so they have removed Anode Filter and few resistors were also missing , i have checked the caps around the CPU and values are not in range way too high 0.065V which normal range is 0.0,039 to 0.042 and same goes for PP_GPU all the caps around the PMU is good , I can see that i am losing significant value from a resistor which next to the 2 cathode pin denoted R4131 Located right in between FL 4292 AND FL 4212 so the resistor is the middle is giving me 0.556 and normal value on known good Board is 2.665V so i am wondering where does the voltage for the resistor come from ?(source of voltage generator for that resistor?