AHT passes OK - but Mac won't start, is it a hardware issue?

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AHT passes OK - but Mac won't start, is it a hardware issue?

I have a failing 2012 MacBookPro 15" (non-retina), sporting quad-core i7, 16GB RAM and 256GB Apple SSD.

Mac fails to restart - After Apple logo appears, progress goes up half-way, then stops, then screen turns blank for 10-30 seconds, fans hit high, then Mac screen blackens completely, and after 20 seconds more, the Mac will restart itself again - and will continue this loop indefinitely.

Things I've done so far:

1. Started the Mac in Target-mode and connected it to another Mac. Used both Disk Utility, and fsck (in terminal) to verify and "fix" the failing Mac's hard drive. Everything reports the HD is fine.

2. Tried to boot in safe mode (shift key pressed) but for some reason the Mac ignores this, or otherwise - keeps failing the same.

3. Connected my other Mac (functional, in target-disk-mode) to the failing mac, and tried to boot off of the external drive - same failure.

4. Tried using single-user mode - but I can't see any meaningful hint for what is my problem. looks like it boots fine.

5. Ran AHT (Apple Hardware Test). It said it'll take 3 minutes for the simple test - but took 10 minutes, then reported the Mac hardware was OK.

6. Tried to zap PRAM (cmd-opt-P-R) several times. No good.

7. Tried to boot in Recovery mode. Sometimes it started OK (and let me run all those utilities, that say everything's fine) but one time the screen turned all blue, with vertical stripes every inch or so.

Now I'm stumped. How can I KNOW I have a hardware/software problem?

Should I erase the Mac completely and spend hours reconstructing everything, just to know for sure it's a hardware issue?

MacBook Pro, macOS High Sierra (10.13.6), 2012, Quad-i7, 16GB, 256GB SSD

Posted on Sep 2, 2018 5:33 AM

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Answer 1

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Encryptor5000

Level 5

7,662 points

Sep 2, 2018 4:49 PM in response to Motti.Sh

Hi Motti.Sh,

Single User Mode stops the boot process immediately after launchd is loaded. The error you're describing might be happening later in the boot process.

Could you please do the following:

Hold down Command-V as you turn on or restart your Mac. This will enable Verbose Mode; your Mac will still boot normally but you'll see the Single User Mode environment as your Mac starts up.
Try to take a screenshot of the text just before your Mac restarts (or when the text hasn't moved for a while). It will likely show the error that is causing the kernel panic (which results in an automatic restart).
Post the screenshot here.

Also, when running First Aid, the result icon it presents isn't always accurate. To expose any errors that First Aid (aka fsck) ran into, simply click "Show Details" as you run First Aid.

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Answer 2

macjack

Level 10

111,242 points

Sep 2, 2018 5:38 AM in response to Motti.Sh

AHT isn't a very sensitive test. Apple has much more comprehensive tests they can run. If AHT reports errors you can be sure there is one, but juat because it reports no errors doesn't mean there isn't one.

You can check for hardware vs. software by installing Mac OS on an external drive and booting from that. If it works as expected then it's software.

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AHT passes OK - but Mac won't start, is it a hardware issue?

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