MacBook

 is a line of high-end laptops made by Apple Inc. There were two generations of portable computers sold as MacBook, they aren't related and don't share parts between them.

White MacBook
The "White MacBook", or Polycarbonate MacBook, was Apple's replacement to the iBook line when they switched processors from PPC to Intel. They were sold from 2006 until 2012, and are encased in a white plastic enclosure. (table1)

Known Faults: to be done

12" Retina MacBook (A1534)
The 12" MacBook, known collectively as the A1534, was introduced in 2015 by Apple and discontinued in 2019 (after not receiving an update for a two years). It was a completely unique design, sharing only its name with the previous MacBooks. The device was unique among all MacBooks in that it was fanless, however this has made the device prone to failures from thermal stress.

CPU
The most common fault among all A1534's is CPU failure, seemingly caused by thermal stress. This is colloquially referred to as "Popcorning" the CPU.

In nearly all cases this renders the device economically unfeasible to repair, as CPU replacements are excessively laborious and costly, if replacement CPU's can be found at all. It is speculated that this is primarily caused by the processors alternating between boosting their clocks and hitting their thermal limit, dropping the clock speed until they have cooled, then increasing their clock speed again, repeating the cycle.

It may repeat this cycle multiple times per minute, each time cycling from around 64 to 90 degrees Celsius. This behaviour can be observed by installing "Intel Power Gadget" on a functional A1534 running macOS 10.14 or earlier, and opening a web browser, or by performing any other light processing task that triggers Turbo Boost.

While knowing this will not help you if the CPU is already dead, disabling "Turbo Boost" can prevent functional CPU's from dying in the first place. "Turbo Boost Switcher" is a third party application available that will prevent the chip from "Turbo Boosting", and instead hold it at the stock clock speed. While this does reduce performance somewhat, it may drastically extend the lifespan of the device, as well as keep it cool. Nominal temperatures with "Turbo Boost" disabled are anywhere from 40 to 60 degrees Celsius.

Should you repair this device for other reasons, you may want to suggest the customer install this program to prevent the CPU from dying. This may prevent them from returning with a dead device, demanding you fix it again and refund them, and instead result in them complaining that the device is slower.

I'll leave it to you to work out how to explain to them the trade-off here, or if you think it better to simply leave them ignorant.

Quirks
On all A1534's there is a small button covered in kapton tape next to the battery connector, this button will totally (but not safely) power down the machine. Before proceeding with any repair, and after shutting the machine down normally (if possible), it is strongly recommended you press this button before continuing. This will kill power to all chips on the board and prevent the system from being damaged.

You may see an LED illuminated on the other side of the battery connector, if lit this LED should go out after pressing the button.

This button is important because unlike many other models where the battery connector can be disconnected from the motherboard before you disconnect peripherals and remove the motherboard, in the A1534 the connector sits underneath the motherboard, and the only way to disconnect it is to either remove the motherboard entirely or insert a battery isolation pick (available from iFixit). As you more than likely want the battery disconnected (or power flow interrupted) before disconnecting anything from the motherboard, to prevent inadvertent shorts, this button is rather important.

Reassembly
This only applies to original generation A1534's, branded as "Early 2015" (see chart above). When reassembling the unit, before starting it up normally, or connecting any other power adaptor, it is important to connect the device to a 5 Volt power source, such as a fixed voltage USB AC Adapter. Failure to do this may result in "permanent logic board damage".

This is as simple as connecting the device to a 5V USB AC Adapter with a USB-A to USB-C cable, and waiting for the startup chime (which shouldn't take long so long as the device's battery isn't fully depleted, typically under 10 seconds).

Using a USB-A to USB-C cable makes it difficult to accidentally connect the device to a USB-PD power source which may, at this early stage, damage the device. After you've heard the chime, you can disconnect the 5V USB source and charge it any other way you please, such as through USB-PD, or turn the device on normally.

Resources
For help identifying MacBooks, see: MacBook Board Number to Model Table

Model information source: Identify your MacBook model