Mac power on self test

How to power a Macbook using a DC power supply!

Your manual will tell you how to get at the RAM, or go to www. Four and five beeps indicate problems with the system ROM or processor, while the Air also has an 'SOS' code consisting of three short, three long and then three short beeps. If you hear these, seek professional Mac help. If something's amiss with your Mac, copy off as much data as you can before anything else happens. Turn off the problem Mac, leaving the other running. Unplug any FireWire peripherals and connect a FireWire cable between the two use one with a 6-pin connector, not the 4-pin video camera plug.

Start up your problem Mac, holding down T. This is the target Mac, while the other is the host.


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The target should appear as an icon on the host's Desktop, and you can drag files off it. Startup might stall with a plain blue or grey screen, a flashing question mark, a broken folder icon, or — rarely — a 'sad Mac'. Sometimes, especially in the last instance, you may have a hardware problem, but let's look on the bright side. Installed Snow Leopard and got a grey screen?

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It could be incompatible or conflict with another peripheral; unplug everything and restart. The same goes for other internal upgrades.

Nothing so obvious? Try a Safe Boot, which adds extra self tests. Shut down, then start up while holding Shift. If this works, immediately try a normal restart. Otherwise, reset the PRAM. When the OS crashes it can only bow out with the message 'You need to restart your computer'. This is a kernel panic.


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It's rare and, thankfully, often fixed by restarting. If not, try unplugging all add-ons from your Mac and restarting. Another possibility is that a system file has become corrupted.

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How to Keep a Mac Efficient and Well Maintained—Part 3

Restart while holding x ; if this works, go to System Preferences, click Startup Disk and ensure the correct disk is selected. Or, restart holding down Option , releasing it when icons appear; you'll be asked which disk to start up from. Or zap the PRAM see the tip above.

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If none of those work, perhaps you've moved, renamed or deleted a system file. Reversing this may sort it out — or not. The next step will be to turn your Mac on. When you perform this step, you want to carefully listen for one or more of the following sounds.

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First, listen for the Mac startup chime. If your Mac is earlier than a late model, it should produce a startup chime. If you have an attached keyboard, you can try pressing the caps lock key to see if the caps lock indicator light turns on, indicating there is power present at the keyboard. If you find no evidence of the Mac turning on, try the test again using a different power cable, a different outlet, or bypassing any power strip or UPS you may be using. For MacBook users, make sure the battery is charged. You may need to leave your Mac plugged in to charge the battery if it was fully depleted.

You already performed a basic power cycle when we started this sequence of tests by holding down the power button for 15 seconds. This time, however, the sequence is slightly different. Hold down the power button for 15 seconds to ensure your Mac is turned off, then unplug your Mac from any electrical outlet and wait 30 seconds.

Power-on self-test - Wikipedia

Plug your Mac back in, turn it on, and listen for any of the startup noises we mentioned earlier. There can be a number of issues that can prevent your Mac from completing the startup process. One of the first steps I suggest performing is to disconnect all of your peripherals, except for the display, mouse, and keyboard. This includes any external drives, printers, expansion boxes or hubs, as well as any cables associated with them that are connected to your Mac. Once everything is disconnected, restart your Mac.


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At this point, the task is to try each item, one at a time, to discover which one is causing the problem. If a problem is detected, your Mac emits one or more tones, or it may blink certain indicator lights to reveal what the issue may be. One tone, repeating every five seconds: No RAM installed. Possibly indicates failed or poorly installed RAM.

How to Use Apple Diagnostics to Check for Mac Hardware Problems

Your Mac will attempt to auto recover from this condition. Do not interrupt the process; once recovery is successful, your Mac will restart on its own. There are a number of possible issues, including no startup disk being found, a startup disk needing minor repairs, a startup disk gone bad, or a few basic Mac settings that need to be reset after all the fooling around with power and POST issues. The SMC controls sleep settings, power functions, battery control, and quite a bit more. They are especially useful for fixing minor drive issues that may be causing your Mac to fail during the startup process.

It also gives you access to Terminal for advanced troubleshooting. White or Gray Screen: If you find yourself stuck with a white or gray screen when you try starting up your Mac, this sequence of tips can help you finish booting to your desktop: How to Recover From a White Screen When Booting a Mac. Luckily, the Mac has the ability to run a built-in hardware test to pinpoint possible problems. Saved my sanity today! I unplugged the power source for 30 seconds as you suggested. Plugged it back in and it responded, thank you for saving a very busy morning and reducing my stress!!