![]() You have to use a tool that reads sensors like hwsensors, or boot into a Linux distribution to check your sensors, then chase down the circuit responsible for that sensor using the schematic/boardview. When a sensor is off, and it thinks the voltage/amperage is too high/low somewhere, or that the temperature is too high/low somewhere, it will clock the machine down and cause the fan to run at max RPM. The machine running exceptionally slow with the fans spinning fast denotes a sensor issue. 99% of the time this turns out as a no fix, usually bad iGPU or MUX communication issues. When you find that 5 V is still missing on L8300 and LCD_PWR_EN is missing on U8300, do not chase. Screen cable needs reseating (this fixes it a surprising amount of the time).But it is the only option since this screen is no longer available. You can fix the screen if the capacitor/connector on the screen is bad, it just sucks to do. If the screen is shorting the backlight to ground, you can fix the screen if the capacitor/connector on the screen is bad, it just sucks to do. USING WRONG SCREEN! If you use a 2012 or a 2015 screen on a 2013–2014 A1502, IT WILL NOT WORK!.If backlight voltage is 49–50 V, bad screen. Trace of backlight output interrupted (can be caused by corrosion, can be fixed with jumper wire)Įxample: (Repaired all corrosion including: LED driver replaced, SMC reflow, Thunderbolt chip replaced, screen connector cleaned and connections resoldered, several corroded components in memory area and screen power area replaced, jumper wire for screen backlight output).Short to ground on backlight output (if backlight fuse blown, check this).This board has a current sensing circuit in place that keeps the backlight fuse from blowing if there is a short to ground on the backlight line. Blown backlight fuse rarely if ever happens.Make sure the issue is no backlight, and not no image! If PPBUS_G3H is 12.56 V, then you probably have a bad battery. There is a shared data line between the battery, SMC, and ISL6259(U7100). On rare occasion U7100 can pull down the data lines. If it is 12.23 V, the SMC is not communicating with the battery on its data line, either because the SMC is bad, or because the pull-up resistors on the data line are bad. Keyboard bad, shorting PP3V42_G3H to ground or power button stuck on.Corrosion of the SMC solder connections.SMC not working(if SMC is off, you will have 12.23 V on PPBUS_G3H instead of 12.56 V) because it is dead, not turning on (SMC_RESET_L low).Įxample: (U5110 (chip responsible for SMC_RESET_L) not working).16–20 V on ADAPTER_SENSE means charger voltage is leaking into ADAPTER_SENSE, below 2 V means it is missing usually due to a bad DC in board. ADAPTER_SENSE not 3 V due to bad DC in board.Unplug it, see if it works (short on 3.3 V or 5 V rail on the I/O board can cause this problem).Įxample: (replaced U1950, capacitor and resistor) Sometimes shotgun replacement of the chip is a clean solution. PM_SLP_S4_L missing for random reason, thoroughly inspect clock chip, tiny specks of corrosion next to it can kill it.U7100 area and Thunderbolt T29 Boost Regular cleared, corrosion removed and replaced. Major corrosion around U7100 (ISL6259) area. U7100 ISL6259 bad, shorted current sense resistors R7121 and R7122 to ground through the U7100. No power, PPBUS_G3H 4 V instead of 12.56 V ![]() Ribbon connector to keyboard bend/dirty/broken (bend back/clean/replace)Įxample: (second repair, ribbon connector bend/dirty)
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