Chosen Solution
Hi: I have a Macbook Pro A1278, which one, I tried to realize a internal cleaning and after reassembling, and turn it on, The equipment, boot, chime and the screen, flash for a second, but nothing else: the screen is black, no keyboard backlight, no power led indicator, fan, hard drive spin, light if Caps Lock press, even the Magsafe led is off. I tried connecting a external monitor, and it works. The battery since begining was dead, but, the laptop worked. I already tried: Reseting SMC, Reseting PRAM, Pressing Option key on start up. and nothing works :(
I would take out the board again and re-assemble, making sure all the connections are secure and that you didn’t miss any. But first I’d disconnect the video cable and re-attach it, making sure the latch is in place, because sometimes even a slightly loose video cable will cause no video or no backlight. When it powers up do you see a faint image (shine a flashlight through the Apple symbol from behind)? If you do, then you likely either have a bad screen panel (bad bulb) or a blown backlight fuse on the board. But the fact that the power LED is not working points to bigger issues, which is why removing the board again makes sense. While you have it apart, I would disconnect the DC-in from the board and let the two sit for an hour to discharge…sometimes allowing a “bad charge” to dissipate can cause normal behavior to be restored.
When you cleaned it did you remove the Fan cooling assembly? Because if you did then you probably removed the assembly off of the CPU and the Video chip. And if you didn’t replace the thermal paste before putting that unit back you could have fried the CPU and Video Chip as well. Google videos about replacing thermal paste of your unit and you might see what you might have done incorrectly.
