I checked the voltage at the DC jack’s ADAPTER_SENSE line, which is normally at approximately 3.3 volts and uses the 1-Wire protocol to communicate with the power adapter and control the LED on the power adapter’s MagSafe plug. Since I was able to press the MacBook’s battery indicator and get some response when connected to power, I knew that the main input fuse was intact, and that the SMC ( System Management Controller) chip was receiving power via the PP3V42_G3H rail and functional the G3H (G3-Hot) designation means that the power rail is always on, even if the computer is otherwise turned off.
I reconnected the AC adapter and started to check the voltages around the DC input jack and its surrounding support circuitry. OpenBoardView in use, showing what F9700 connects to, and where.īefore any device can perform any useful functions, it needs power. There was clear evidence that it had suffered from liquid damage: rampant corrosion around the LCD connector and some of the power circuitry, and some of the corrosion deposits were even left on the computer’s bottom cover! If you watch Louis Rossmann’s videos, you would know that liquid damage rarely is an easy fix, especially when high-voltage LED backlight circuitry gets involved.į9700 (backlight fuse) as shown in the schematic, which can be looked up in the board view. Unscrewing the bottom cover revealed what horrors the computer had experienced. With this functionality test being unsuccessful, I decided to open up the computer to see what else was wrong… Troubleshooting & Diagnosis As previously noted, the computer had a laundry list of issues that were certainly the reason the original owner decided to discard their computer – a laptop that doesn’t boot nor have a display isn’t a particularly useful one.Ĭonnecting a MagSafe AC adapter to the computer revealed even more issues: even though the unit was already noted that it wouldn’t charge, I noticed there was no LED indicator on the power adapter’s plug, and the computer wouldn’t power on, even with external power connected the only sign of life was one of the LED level indicators rapidly flashing when I pressed the button.
The computer I picked up is a mid-2012 MacBook Pro by Apple it is the A1278 model with a logic board number of 820-3115-B, and it comes with an i7-3520M CPU and 8 GB of DDR3 RAM – however, the hard drive was taken out of the computer by the time I received it. It certainly didn’t look particularly promising, but I felt it would be a good way to test my skills in component-level repair – with a pretty nice prize if I succeeded. It had a note attached to it citing several issues with the computer: the display doesn’t work, the battery doesn’t charge, one of the USB ports doesn’t work, and it won’t load an operating system. A couple weeks ago, I picked up a dead MacBook Pro that was on its way to the recycle bin, and was curious as to whether I would be able to fix it.