Hello. I am very new to macbook logic board diagnosis and this one has me totally stumped.
Presentation:
I have a MacBook Air A1932 that showed up to my shop with a lightning bolt charging symbol on all the time (when plugged in and when unplugged). The unit would sometimes restart on its own and was giving a different battery percent each time it was powered on. I disassembled the device and began testing. After the battery was unplugged, the device will no longer show that it is charging even when plugged in. When the charger is plugged in, the unit produces the charging ding, with no change to the battery icon.
Diagnostics:
When plugged in, the charger will successfully supply 20V without delay. With the battery plugged in, the unit draws ~1.5 A from the charger. The battery is at ~11.7V (is that overcharged?) and the voltage across PPVBAT_G3H_CONN is at 12.4 V when charging. SMBUS_3V3_BATT_SCL and SMBUS_3V3_BATT_SDA are both biased to 3.3V. D6959 (DIM LED) is lit only after charger is plugged in and stays on when unplugged (The battery does not output anything until SYS_DETECT_L is brought low by PP3V3_G3H_RTC. I am assuming this is an intended safety feature as the pull down resistor on that line is missing from the board, and only PP3V3_G3H_RTC can bring it low). PPBUS_G3H is at 13.1 V when the charger is plugged in and 12.0 V when on battery power. PPDCIN_G3H is at a steady 20.0 V. No liquid damage indicators are tripped and no corrosion was found anywhere on the board.
My best guess:
I'm not too familiar with how MacBook charging works, but I understand that ISL9240HI (U7000) is responsible for switching power between the battery, the charger, and PPBUS_G3H. There are two current sensing circuits on that page of the schematic, one for sensing current from the charger and one for sensing current to/from the battery. I tested all the resistors on both circuits and they all check out. I still think one of these circuits is causing a problem, and either a bad reading or no reading at all is causing either ISL9240HI or the SMC to miss out on the fact that the battery is indeed charging. If this were the case however, I would have expected to find a bad resistor in the circuit, and I would expect that ISL9240HI would close Q7065, preventing the battery from overcharging. Neither of these are the case. I am not an expert on current sensing circuits by any means, and I'm sure I'm not testing it thoroughly. Given what I know, I want to change out ISL9240HI but it doesn't look damaged or corroded, and it appears to be functioning normally otherwise. Plsbro help me figure out what I'm missing.
Thanks for the help and happy holidays!
Presentation:
I have a MacBook Air A1932 that showed up to my shop with a lightning bolt charging symbol on all the time (when plugged in and when unplugged). The unit would sometimes restart on its own and was giving a different battery percent each time it was powered on. I disassembled the device and began testing. After the battery was unplugged, the device will no longer show that it is charging even when plugged in. When the charger is plugged in, the unit produces the charging ding, with no change to the battery icon.
Diagnostics:
When plugged in, the charger will successfully supply 20V without delay. With the battery plugged in, the unit draws ~1.5 A from the charger. The battery is at ~11.7V (is that overcharged?) and the voltage across PPVBAT_G3H_CONN is at 12.4 V when charging. SMBUS_3V3_BATT_SCL and SMBUS_3V3_BATT_SDA are both biased to 3.3V. D6959 (DIM LED) is lit only after charger is plugged in and stays on when unplugged (The battery does not output anything until SYS_DETECT_L is brought low by PP3V3_G3H_RTC. I am assuming this is an intended safety feature as the pull down resistor on that line is missing from the board, and only PP3V3_G3H_RTC can bring it low). PPBUS_G3H is at 13.1 V when the charger is plugged in and 12.0 V when on battery power. PPDCIN_G3H is at a steady 20.0 V. No liquid damage indicators are tripped and no corrosion was found anywhere on the board.
My best guess:
I'm not too familiar with how MacBook charging works, but I understand that ISL9240HI (U7000) is responsible for switching power between the battery, the charger, and PPBUS_G3H. There are two current sensing circuits on that page of the schematic, one for sensing current from the charger and one for sensing current to/from the battery. I tested all the resistors on both circuits and they all check out. I still think one of these circuits is causing a problem, and either a bad reading or no reading at all is causing either ISL9240HI or the SMC to miss out on the fact that the battery is indeed charging. If this were the case however, I would have expected to find a bad resistor in the circuit, and I would expect that ISL9240HI would close Q7065, preventing the battery from overcharging. Neither of these are the case. I am not an expert on current sensing circuits by any means, and I'm sure I'm not testing it thoroughly. Given what I know, I want to change out ISL9240HI but it doesn't look damaged or corroded, and it appears to be functioning normally otherwise. Plsbro help me figure out what I'm missing.
Thanks for the help and happy holidays!
