MacBook Air a1466 820-3427 sensor / voltage issue
I’ve been troubleshooting my own liquid-damaged Macbook Air and have so far replaced the following:
- IO board - with known working used (had corrosion)
- IO flex cable - with new 3rd party
- top case and keyboard - with known working used (had sticky keys)
- trackpad flex cable - with new 3rd party
- trackpad - 3 times - with known working used
I have inspected the logic board thoroughly with a microscope. A tiny trace of corrosion was present on R8167, cleaned with iso, flux and reflowed component. The rest of the board was clear, but I cleaned the whole board with iso and oven dried before letting it sit for a few days before re-assembling.
Each of the 3 times I have replaced the trackpad, I’ve managed to get this Macbook to work flawlessly, each time it works for roughly two weeks before the same issue presents itself, these 5 temperature sensors stop reporting and kernel_task kicks in causing fans to spin at max and laptop goes into limp mode:
Common point of failure has been suggested by others to be the flex cable, so I have ordered another new replacement flex cable. Apple Diagnostics always displays a PFM code for an SMC error, but it seems unlikely that the SMC chip itself would work intermittently in this way.
I should note that orange/green light works as expected, with and without the sensor fault, and battery is taking charge. Laptop functions normally aside from the thermal throttling.
Looking at some of the voltages and amp readings reported by iStat Menus however, I am concerned, in particular the CPU voltage of 1.72v seems to me to be high for a laptop CPU. PBus rail seems a little high also.
I have OpenBoardView schematics for the board, but cannot find a reference for the correct voltages and amps I should be seeing. Are any of these voltage or amp readings indicative of a problem anywhere else on the board?
I’m somewhat comfortable reflowing/replacing components and checking rails with a multimeter but I do not have access to MRI or AST and without a reference sheet I am a little lost.