Mid 2009 Model A1278 / 2.26 or 2.53 GHz Core 2 Duo processor EMC 2326

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Why does my MacBook Pro fan spins fast when plugged in.

My Macbook Pro Mid 2009 won't boot. The moment I connect power thru magsafe, the fan spins in full speed even without pressing the power button. I know the battery is drained because I tested it with another machine and shows 0% so I charged it full and was working ok in the other machine. Tested the working battery from machine 2 and again fan spins fast the moment I connected the battery connector. The charge indicator at the side doesn't show up any light even though the battery is connected and full. The magsafe green light indicator lights up normal the first 1-2minutes then slowly fades out that you could hardly see the light. Is is a short circuit somewhere? I tried pulling out most of the connectors inside like HDD, DVD, WiFi, display connector and fan but no joy.

Please someone help me. I don't know the history of this computer as I bought it online second hand. The previous owner didn't mention anything about liquid spills. He just said it was running then he closed the lid and never woke up from sleep, didn't boot. I removed the HDD and installed a fresh Mavericks from another machine but still no joy. I tried doing SMC reset (so I had to install battery as normal, magsafe power adapter plugged in - so the fan is spinning fast) but when I press shift+control+option then the moment I press the power button, the fan stops spinning and when I undress the power button spinning resumes.

Got no choice but to unplug power and disconnect battery again to make the spinning fan stop.

Thanks and hoping for someone to reply with a solution.

Answered! View the answer I have this problem too

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correction: the fan stops spinning and when I "unpress" the power button spinning resumes.

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What happens when you disconnect the keyboard ribbon cable. Does the fan still power up when you plug in the power adapter? If it doesn't then you know the problem is within the upper case.

Now lets test it again this time using the power pads:

With the keyboard ribbon cable still disconnected just above the connector you'll see a two large silver pads of equal size carefully short across them with the power adapter plugged in (and everything else installed). Your system should startup now. Does it? If it does you know the issue is only the power switch in the cover. If not, you have a logic board issue.

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I got the same issue with my 2006 mbp. It was a bad I/O cable.

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