Random iMac shutdowns continue

Users continue to report an issue in which various iMac models randomly shut down during routine operation. As described by one user: "...it randomly has shut down on me at least 12 times since I turned it on. I can restart it and it'll stay on for a long time. But then, randomly it'll shut itself off again."

This problem has been reported by several other users, but one user has a unique situation in which his computer restarts at the slightest vibration, indicating a hardware fault of sorts in the power system, potentially due to faulty wiring.

It is possible that a batch or two of iMacs have faulty wiring that have caused, or at least contributed to, these random shutdowns and restarts. In the case of the iMac that's sensitive to touch, it's very possible a loose connection in the power system causes the thing to disconnect and shut down. Additionally, one user reports that setting the computer to restart after a power failure causes the system to restart instead of shutting down, adding further evidence that this is a hardware problem.

Some users report that getting their iMacs' power supplies replaced by Apple resolves the issue.

As previously reported, some users have also had success with the following fixes:

Reset SMC

1. Turn the computer off
2. Unplug all cables from the computer, including the power cable and any external device cables.
3. Wait 30 seconds.
4. Plug the computer back in and connect the keyboard/mouse, then turn it back on.

Re-seat RAM The problem could also be improperly seated RAM modules. Try removing the RAM modules then firmly seating them back in place.

As described in Apple Knowledge Base document #303083:

"If the computer detects no SDRAM (Synchronous Dynamic Random Access Memory, also referred to as RAM) or the RAM installed does not meet the appropriate specifications, the screen will remain black but the power LED on the front of the computer will blink once per second to signal the error. This error condition may be due to physically damaged RAM, installing the incorrect type of RAM, or not having RAM installed."

If the problem continues after performing the aforementioned fixes, the next step is to take the computer in and get the power supply inspect and serviced.

Feedback? Late-breakers@macfixit.com.

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