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Mid 2012 model, A1278 / 2.5 GHz i5 or 2.9 GHz i7 processor.

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MBP charges, but won't power on

I recently bought a MBP (13" mid 2012 A1278) from an acquaintance and I'd like to see if I can't get it working. She says she thinks she shorted the logic board when attempting to clean the fan. She said she forgot to take out the battery. I'm guessing when she went to pull out the fan something happened. There's no obvious damage to the board, though. I'll be getting a multimeter this week to see if I can't find out if a particular component is bad.

When connected to an original 60W charger, the light turns orange upon connection, and then green. The front power light does nothing. The charge indicator lights show 5/8 green. I've tried every relevant button combination to power on the device. I've reseat the (OEM) RAM, and tried just one stick. I've reset the SMC. I've tried plugging in the charger with the battery disconnected - still no power. I've tried shorting the power pads - nothing. I've also tried shorting pin #5 to ground. I've got an 85W charger coming in tomorrow that I'll try out, too.

Any other suggestions would be appreciated. If anyone has a decent idea of where to start checking connections on the board, that would also be greatly appreciated!

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Try a PRAM reset, Command-Option-P-R.

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Disconnect everything except the fan and charger port, then plug the charger in. If it is not turning on, it is a problem with the logic board.

There is a chip below the fan (top right of fan connector), feel this after a minute of leaving it plugged in to see if it gets hot. Also, feel the chip to the top right of the RAM, which says ISL6259A on it.

If either are getting hot, the chip or a component linked to the leg of the chip are shorted to ground and need replacing. If you have the tools to microsolder, experience and a multimeter, I can tell you points to measure if these chips aren't getting hot. If you would not be able to replace components on the logic board, there is no point troubleshooting it beyond my first paragraph; just send it to a repair shop who deals with logic board repairs daily.

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Thanks Reece. I disconnected everything and no chips got remotely warm. I wasn't able to locate a chip labeled ISL6259A. I've got pretty limited experience, but I don't have anything to lose, so I would try out replacing any failed parts. What should I start measuring?

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Grab a schematic and board view file for the 820-3115 (check on the top of your board to verify this is your board number, you will see it etched in somewhere).

Open the board view file (download openboardview to do this) and search net for the following, measuring the voltage as you go; PPBUS_G3H, PP5V_S5, PP3V3_S5.

Let us know the voltages

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Thanks Reece, here are my readings:

PPBUS_G3H - 200mV

PP5V_S5 - 42.2mV

PP3V3_S5 -173.9mV

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Issue is most likely with PPBUS_G3H as long as it is getting charger voltage, since this supplies the others. Check for a short to ground on this line

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PPBUS_G3H measures 12.62 V to ground, with ~0.0 V drop.

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I would do the PRAM Reset with everything unplugged Command-Option-P-R.

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