Chosen Solution
Hi all, We have a water damaged 6s that draws no power when the battery is connected, our USB Ammeter shows that with the battery connected draws 0.00mA but when we disconnect the battery we get 0.04mA-0.07mA. It is a water damaged case and this has undergone a lot of ultrasonic cleansing. It did have a VCC_Main short on one of the (really) bad caps which has not been alleviated (I think a total of four caps, two of which weren’t even fully connected were removed). At first I was thinking U2 because when I connected the USB dock to the Ammeter and tested the battery terminals for voltages, I was getting 0.03V which is really low (have had a previous case like this where that is how I determined a U2 failure) I did do a U2 swap which I am quite confident with and the 1.80V and 3V voltages it gives out are ok but I am in the same boat. From this point on I’m wondering what avenues would be good to explore?
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 they are not shorted, then you can connect, preferably, a known-good battery (or a current limited DC power supply with the appropriate connector adapter) to see what voltage you measure. If the voltage is low or lower than the battery voltage (which you measured before plugging it in ;>), then there could be a short circuit on secondary subsystem that is causing the battery or DCPS to be current-limited. If you are measuring the proper voltage, then you move onto the PMIC and check the voltage rails it generates. The PMIC generates a lot of voltages so you will want to check the main ones related to the CPU/GPU/SOC/SDRAM/NAND etc first. If everything looks good there, then look at the baseband PMU outputs and the I2C lines. At some point, you will find some leads to work on.
