Diagnosing Apple computers
For Apple computers, open the link: https://support.apple.com/en-us/HT201257
On startup, hold down the D key on the Mac machine. Follow the guide in the link to determine if there's a detectable hardware issue with the machine.
Use your Serial Number on the computer to browse the options for diagnostics, updates and other information about your device.
If your computer turns off unexpectedly, this link will help you resolve this problem.
SMC and PRAM:
To reset the System Management Controller, hold down the Control - Option - Shift and Power buttons, at the same time, for 10 seconds. Release and wait for 3 seconds to hit the power button to turn it on. This test will reset the connections to the devices on the computer.
The SMC is responsible for these and other low-level functions on Intel-based Mac computers:
- Responding to presses of the power button
- Responding to the display lid opening and closing on Mac notebooks
- Battery management
- Thermal management
- Sudden Motion Sensor (SMS)
- Ambient light sensing
- Keyboard backlighting
- Status indicator light (SIL) management
- Battery status indicator lights
Selecting an external (instead of internal) video source for some iMac displays
To reset the Parameter Ram:
Step 1: Turn off your Mac. No need to remove the battery or detaching the power chord.
Step 2: Turn on your Mac and hold down the Command+Option+P+R keys, all at the same time.
Step 3: Hold down all four keys until you hear the startup sound twice.
The startup sound for the second time means you’ve reset the PRAM.
Article Id #22022