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6s Plus no power, not tristar nor tigris
Hello guys (and girls, if any) I bough a 6s Plus dead, thinking it was going to be an easy tristar job. When I got it I plugged it in to a charger and it was charging normal current, around 1 amp. When I opened it up I found that tristar has already been replaced. Plugged my DC power supply and it starts normal: 80mA, then 100mA and it stays there forever (quite like if it were in DFU mode, but I get no backlight nither it is recognized by iTunes)
At this point I replaced tristar in case the replacement was bad. Then replaced tigris, no dice. Then I replaced both at the same time since I've seen some that can kill the other if it's bad, but then again it was actually charging even before I opened it.
After this I found a shorted line on Chestnut output, that would explain if that chip was bad why it wouldn't boot. Turns out the chip was fine, just a shorted cap so back to square one.
At this point I have no more clues. All I2C lines are not shorted, which would've explain why not booting. Anyone seen anything like this? or which way should I continue?
Any and all help is appreciated!
Regards from Argentina, Rodrigo!
It's really tough to say. It could be just about anything. Since you don't have a history of the device, it'll make it even harder to diagnose and repair. You can start with diode moding all of the main power lines (vcc_main, pp1v8, pp3v0) and comparing it to a known good board. From there, you can branch out to the sub power lines like, pp1v8_nand and pp3v0_nand, etc. All it takes is one bad cpu line to make the phone do what you're saying.
Okay so all power rails are present except for PP_GPU and PP_GPU_SRAM, which I'm guessing it's not being told to turn on just yet, maybe CPU is locked up expecting some data line that it's not getting. All data lines I was able to check had normal diode mode readings.
Is there anything else I could check before I start pulling ic's that could prevent the board from booting off?
This is a tough situation for all of us. If you've measure most main power lines and i2c lines in diode mode and compared them to a known good board, then I usually just stop there. If you are trying to learn, then yes, I think the next logical step is to remove unnecessary boot ICs. If that still results in nothing, then you would have to assume the CPU or PMIC.