Chosen Solution
Hello, I do have an iPhone 6s here, which won’t power on. As this is a too generous description, I did some measurements before asking here. First thing was to replace the battery with a working one. But this doesn’t changed anything. Although the original battery reads 3,7V and my known working one has about 4V. Then I recognized that the phone is taking current from the power supply. I always use a tool (Muker-017) to measure the current ;) First strange thing was, that with the battery connected it draws about 0,46A, on my working iPhone 5s it takes 0,96A. Second strange thing, I put in my known working battery and plugged in the charger. Surprisingly now it dosen’t take any current 0A, no charging. No it becomes more interesting. I disconnected the battery and plugged in the charger. Now it takes 0,23A although it shouldn’t take any current. First thing I was thinking about is a short somewhere. So I pulled out the Mainboard and first checked for a short on VCC_MAIN, but it is not shorted. After letting the Mainboard for one minute plugged in I recognized some warming around the CPU area. So I removed the CPU shield and the covering on the other side. There I measured all capacitors to maybe find a short. But they are not shorted and look ok. The great question is now, what ideas do you have? Should I take any further measurements? If so, what measurements? Have you ever faced a similar problem and know out of the box whats going on? ( would be the best answer ;) ) I don’t think this is a Tristar issue, because it measured 3,7V coming in at the battery connector. Could it anyhow be a Tristar issue? Please see the picture to know what area is getting warm, when USB charging is connected while the battery is disconnected.
I hope someone can help here. Thank you for your time and tips ;)
When dealing with a “dead” phone, there is no “silver-bullet” solution. You have to probe the board to get a better understanding of what is working properly and what is not. It may be a simple solution or a complex one. Sometimes we see a visibly blown cap, replace and all is well. Other times, everything looks perfect yet the phone won’t boot. You have to start at the beginning and check PP_BATT_VCC, PP_VCC_MAIN and PP5V0_USB. I would start by checking to see if those rails are shorted to ground. If one of these rails is shorted to ground, then you will need to identify what is causing the short. It could be a bad decoupling capacitor, conductive debris or defective IC that is directly supplied by those rails. If you are measuring the proper voltage, then you move onto the PMIC and check the voltage rails it generates. The PMIC generates ~15 voltage rails. They are all important (for obvious reasons) but the ones to check first are as follows: PP_CPU & PP_GPU – These rails supply the CPU & GPU. They are low resistance rails so they may “beep” when you test them on your multimeter in continuity mode. It’s important to look at the reading and not focus just on the beep. You will typically measure something around 20-100 Ohms on these lines.PP1V8_SDRAM & PP1V1_SDRAM – These rails supply the SDRAM (which is sandwiched with the SoC/CPU).PP_SOC & PP_FIXED– These rails supply the rest of the System on a Chip. What we commonly refer to as the CPU is actually a SoC.PP_CPU_SRAM & PP_GPU_SRAM - These rails supply the Static RAMPP0V9_NAND & PP3V0_NAND – These rails supply the NAND chip.PP3V0_Tristar – These rails supply Tristar chip.PP1V2 - Supplies various subsystems including SoC, FCAM/RCAMPP1V1 – Supplies the High Speed Digital Communications via the SoCPP0V8_OWL - OWL subsystem on the SoCPP1V8_ALWAYS – This is an “always-on” voltage rail that is used for the bootstrapping of the device The PMIC also generates, what I would consider secondary, yet still important voltage rails for the following sub-systems: PP1V8_MESA & PP3V0_MESA – Supplies the Home Button TouchID subsystemPP1V8_VA – Supplies the Audio Codec and Speaker AmpPP1V8_TOUCH - Supplies the Touch subsystem on the screen and acts as a pull-up supply for various systemsPP3V0_PROX_ALS – Supplies the Proximity and Ambient Light SensorPP3V0_PROX_IRLED – Supplies the Infrared LED of the Proximity sensorPP3V0_IMU_OWL – Supplies the Compass and sensorsPP3V3_USB – Supplies the USB functionality of the SoCPP3V3_ACC – Supplies power to any accessory connected to the Lightning Port via the Tristar IC. (This line is only “on” for a very short period of time so you only need to worry about shorts, not voltage) Once again, you should start with measuring the rails in diode mode while unpowered to limit any potential damage of excessive current going through the logic board. If there are shorts, do as above to identify any faulty components. Depending on what you find, it may be a PMIC issue or a downstream issue.
what do you mean by a downstream issues exactly? because I had the same problem and I had to give up was a cpu . I dont see any other issue apart pull up and down resistors and ics !!
