Chosen Solution
trying to get data from this phone, like title says its loops 5-10 times then shows no image but backlight stays lit. with only the screen connected its at 230ma and steady after it looped 5-10 times and displays no image. while its looping on apple logo it has both backlight and image. i have ir camera and cant see any shorts and ive probed alot of the power rails all the important ones are there also i tried to update and it failed after sending ramdisk. another note is during update i had it in dfu and it failed to switch from dfu to recovery. so then i put it in recovery and thats when it failed after sending ramdisk
When you have a tough one like this, you have to be systematic in your probing. You don’t say what lines you probed so I’ll assume the “big” ones like CPU/GPU/SOC/SDRAM/NAND etc. You also don’t say what the phone has been through prior to this issue (water, impact) so it difficult to make any specific recommendations. Seeing as how you are not seeing anything obvious such as physical damage, water (?) or any heat signatures, I will suggest however that you check ALL the PMIC lines (the switcher’s and LDO’s) and then if necessary, check the BBPMU outputs as well. I would also check the secondary LDO’s such as MESA, BL, LCM etc. as they can also cause issues with boot by jamming up the I2C lines. Once you are convinced that there are no power issues, you’ll probably have to start pulling major chips until you either figure it out or call it quits :>).
I’m going to guess either you have a bad screen or something is not plugged in correctly. When components of the phone, screen, cameras, home button are not connected it will cause the device to boot loop like this. It could also be a bad battery. Even with it plugged in, Apple devices act goofy when they have bad batteries. The only other reason this would be happening if the other solutions don’t work is that there is something wrong with the logic board or the software.
