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I have been reading posts and people discuss using SMC bypass mode. What does it do? Will a computer turn on and display with a bad or missing SMC if you use this mode to start the computer?
Starting in this mode SMC will not read the board sensors, like voltage, current, nor temperature.
If the board starts, you must check the 2-3 schematic pages where all these sensors are exposed.
Some sensors, like AMON, BMON, can block the board to make any start intent.
Other ones will block the board after some S4/S3/S0 voltages try to appear.
Fan will spin high from the begining in this mode, because SMC will not read temp sensors.