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Lançado em junho de 2012, modelo A1278. Processador Intel com Turbo Boost, até 512 MB DDR5 de RAM vídeo

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Fan spins at maximum speed by turning MacBook on, then shuts down

Hi everyone,

I have a problem with a Macbook Pro Mid-2012 (A1278). When I turn it on, the fan immediately starts spinning at maximum speed. When it gets to the login screen, I log in, and after two seconds of loading it shuts down. I've already tried to reset SMC and PRAM, but that didn't help.

My guess would be that it is a thermal sensor not working properly? Does anyone know were the thermal sensor is located? Or any other ideas?


Update (03/15/23)

Thanks a lot for your help so far.

I did a quick inspection on the pins and also the logic board, from what I can see and judge, it doesn't look too bad.

Here are some photos:

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Block Image

Block Image

I will try to also find someone with the same charger. Although the charger seems to be in quite ok condition and I think is replaced at some point. The only thing I can see is that the chord is slightly squeezed at the top, but I don't think enough to not make it work properly.

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I do see some junk on one of the 470 caps near the fan give it a clean with the isopropyl alcohol and a cotton swab.

You do have a fine coating of dust on the board a soft brush can loosen it and a short blast of air to push it away.

Looking at the MagSafe charger in small white print on the plug side you should be able to not the Wattage what do you have?


Sorry for my late answer!

I just tried a working charger from someone else. Unfortunately the same problem. What is interesting though, is that also with this charger the LED was not lit again. Logic board I didn't have time yet to clean.

Oh, and both my own charger and the borrowed one were the 60W (A1344) charger.


@arjanj - This is starting to look like a comparator logic is damaged. The chip in question is on the other side, you’ll need to take the logic board fully out. Take a good sharp picture of the back side and post it here for us to see.


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Clearly SMC encountered an extreme issue which is likely why the system shut down. I would focus on the power for starters.

What is the color of the MagSafe charger cord LED? Amber, Green or not lit?

After letting it charge does the case feel overly warm around the MagSafe connector?

When did you replace the battery?

The next step would be to disconnect the battery and just try running the system from the charger. Did that also fail?

Update (03/15/23)

@arjanj - OK, we have two problems then! First your battery has past its life expectancy! At best with good charging practice you might be able to squeeze out five years, for most four is at best. Just like a car battery the chemistry breaks down over time. But let’s wait on that until we get the system working correctly with the charger.

Inspect the connector surfaces are the pin surfaces clean both sides? Is the plastic area as well clean? If not I would start there. Post a picture of the system’s MagSafe connector straight in so we can see the pin area zoomed in as far as you can go with your camera.

The MagSafe connection has a one wire comm link to the charger with the middle pin. Make sure it’s not damaged. Often I find the knockoff chargers don’t make good contact so you may need a new one. Did you have a friend with a MacBook Pro of the same series? If you do see if you can use his charger to see if it is working on your system.

If the systems connector looks bad you may want to replace it it’s a bit of work but that would be the next step. Here’s the needed part MacBook Pro Unibody 13" and 15" MagSafe DC-In Board and the guide to put it in MacBook Pro 13" Unibody Mid 2012 MagSafe DC-In Board Replacement.

Also do a good inspection of the logic board for any staining or corrosion or burnt components. You might want to use a small soft paint brush to scrub the board and fans of any dust buildup and using a can of can’ed air to blow it out.

Imagem de MacBook Pro Unibody 13" and 15" MagSafe DC-In Board


MacBook Pro Unibody 13" and 15" MagSafe DC-In Board


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The battery is still the original one.

When I plug in the MagSafe charger, the LED is not lit.

Also maybe good to know, is that when I plug in the charger, it boots by itself, without me pressing the on/off button.

I just tried to disconnect the battery and run the system from the charger, unfortunately same problem.


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Hi @arjanj , Trying another charger would definitely be a great idea, even if the cable or connector itself is not damaged! When power supplies get older, they stop being able to output as much power as they could before, similar to rechargeable batteries! It sounds like the SMC can't detect your battery, so it would entirely be running off the power supply, and if the computer draws what it expects the power supply to be able to handle when it cant, you will definitely experience random shutdowns like this.

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Hi, thanks for your help! I just tried another (working) charger, unfortunately the exact same problem, but also the LED was not lit again.


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Arjan Jongsma será eternamente grato(a).
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