Chosen Solution
Hey all! My MacBook has had some issues that are pretty weird. On power up, it would have no backlight, no charger led, but the screen itself would come on (you could see it by shining a flashlight on it). The computer would boot, but here’s where things get odd. After about 5 seconds of being on the login screen, the computer would “sleep". The backlight never came on. The computer showed the apple logo and stayed on for the duration of the boot, but soon after the login screen showed up it would turn off. I could wake it up again by pressing a button, and it seems like it’s sleeping because if I manage to log in before it shuts off, it wakes up and makes me enter my password again since the computer locked. I opened the computer up and I found that when I unplugged the ribbon cable that connects the left I/O board to the logic board and booted the backlight comes on and I’m able to use the computer normally except for the fact that it’s unbearably slow, the fan is at full speed constantly, and there’s no sound. As soon as I plugged the cable back in, however, the backlight dimmed and the computer went to sleep. The charger light never comes on. Is this the work of a faulty I/O board or is this a bigger issue like a bad SMC?
Inspect your MagSafe connector on the I/O board is it clean and are the pins shiny? Try cleaning using a cotton swab with some isopropyl alcohol. If you need to replace the I/O board MacBook Air 13" (Mid 2012) I/O Board follow this guide MacBook Air 13" Mid 2012 I/O Board Replacement You also will need to inspect the MagSafe charger follow this guide Apple Portables: Troubleshooting MagSafe adapters If your adapter cable is knotted (not smooth) up or damaged in any way you’ll need to replace it but be very careful! OEM MagSafe Chargers vs Cheap Imposters: Teardown for Truth & Compared: Fake vs Genuine Apple Magsafe Chargers You may have some logic board damage from what you describe also implies you had a liquid spill as the display is also failing to work. When you open the system up to replace the I/O board you should take the time to inspect the logic board (both sides) heres the needed steps to do that MacBook Air 13" Mid 2012 Logic Board Replacement Take the time to sub the logic board and the fan of dust buildup using a soft paint brush and a can of can’ed air. Update (04/18/2019) I’m starting to think you’ve got too much damaged here to make this an economical repair. You clearly need a new battery the I/O board (MagSafe) maybe damaged and the lid sensor on the logic board maybe damaged too. As we can’t get any diagnostics given the current condition to even try to isolate out whats bad I think its time to throw the towel in.
