Starting in 2018, Apple integrated the SMC chip to a larger multifunctional chip called Apple T2 security chip in the new Macs. You may need to repeat step 3 to step 5 for a few times.Keep pushing and releasing the button to get the dirt out of the button.Wait for a few minutes until the lubricant softens the dirt.Apply one or two drops of WD-40 lubricant to the button.Put the iMac on a flat desktop with the screen facing down.You can easily remove the dirt without replacing the button by following this procedure: Luckily, most of the time, a failed iMac power button is caused by dirt, not the electrical contact failure inside the power button. You need to remove the iMac screen, the power supply and logic board before you can get access to the power button. iMac power button replacement is a time-consuming task even for a Mac repair professional. The sticky power button is caused by the dirt accumulated inside the button.

If you have a sticky power button or a faulty power button, the power button will not be able to send a valid control signal to the logic board so your iMac will not turn on.

Macbook pro 2015 won t turn on