MBP A1278 doesn't switch on - Maybe faulty component on LogicBoard?

Thanks for your reply!

I already did what you were suggesting beforehand...

When you put in the charging cable, the light turns from green to orange, and when the battery is fully loaded, the light turns to back to green.

If you push the power button on the key, the fan starts to spin, but the display doesn't work. (Can't remember whether the chimes work, I think they didn't).

I will try to detach the display cable on the logicboard when starting in next time.

Obviously, before changing the keyboard itself, I would like to know whether the damaged component could cause that problem.

I've seen on the schematics that it is marked as "CRITICAL", don't know what that means in this case...

It is critical but I think it is just dirty, not damaged. You can brush it with IPA or acetone and a soft toothbrush. If the smudge goes away, and you find no traces of corrosion on the two legs/pads connecting to the board, then I don't think there's an issue.

BUT this is still premature. Keep everything for now, including RAM, fans, and heatsink. Disconnect keyboard if you have not yet, and try to boot. To do that, just plug in the charger. This should prompt it to start up in the absence of a keyboard.

Sorry for my late reply... to be honest, I put the MacBook away because I was tired of it.

I hope you are still reading this or get a notification that I'm replying you now.

Just took the MacBook out of the closet because of boredom and did what you were writing:

>> When cleaning, you need to remove everything including RAM sticks, fans, heat sink... anything detachable from the main board. Drying thoroughly is also necessary.

Done.

>> Then you connect one fan, the small MagSafe board (where the charger attaches), and you plug in the charger. Must be original charger, 60W ok in your case. In case of doubt, use an 85W adapter. So plug in the charger while making sure the pins are properly aligned otherwise you can fry your onewire circuit. After you plug in, you should see a green light and the fan spin.

Did that... the charger turned green, but no fan spin.

>> Unplug power, attach battery, repeat. If now you have green then orange light, the board is basically starting and charging.

Did that, too... the charger is green at first, but then switches to orange. Unfortunately, again no fan spinning.

>> Again, disconnect battery and power, put board back in the case, and attach keyboard, then battery then power (ALWAYS disconnect power charger and battery between tests). Next attach the screen, also disconnect power and battery until you have it plugged in. If the green and orange lights don't turn on after you plug a certain component, you can assume it is causing a short and preventing the laptop from restarting. Report back.

Done... I attached each component one after another and observed what the charger light is doing. Each time it changes from firstly green to orange.

I then tried to switch it on (normal power button!). You can hear that the hard drive starts to spin, but no screen activity.

Afterwards, I tried to reset the SMC (Shift, Ctrl + Alt) and the battery light changes from orange to green, and after a few seconds back to orange. So the reset works, and the MacBook tries to start, but:

a) HDD spins

b) Fan doesn't spin

c) No display activity...

I'm afraid I don't know anymore what to do now...