It’s been a while since I did any repairs. A little while ago I bought two MacBook Pros off eBay from two different sellers. They both had incorrect descriptions, and both had been exposed to liquid at some stage, and then put away for several years, resulting in a logic board riddled with rust. It was totally impractical to even attempt a repair, so I just salvaged the parts I could.
Needless to say, this left me a little wary about making another purchase. It does seem to be getting harder to find good, profitable repair projects.
Anyhow, I started getting a bit bored, and keen to take on another project, so I bought this one on eBay for $180. It was described as “doesn’t turn on, doesn’t charge, unknown if there’s other faults”. The last five words are a little scary, because that usually means “there are a hundred other faults”. But I was able to double check the specs from the serial number, and the laptop included RAM and a hard drive. I decided it was worth a try.
Once it arrived I noticed it had a significant dent in the top case (hear those warning bells going off!) but apart from that it looked pretty clean. And after a quick inspection, it didn’t look like anyone else had attempted a repair, which is very nice to see.
I started by plugging in the charger, and immediately I got a green light and the laptop spun into action. Fan spinning, startup chime, everything. But the joy was short-lived on two counts. Firstly, it came alive for just long enough for me to see a huge crack in the LCD screen. And secondly it switched itself off after just a few seconds, and then wouldn’t come back on again (or even give me a green light on the charger).
I can’t say I was very surprised about the cracked screen, given the size of the dent on the other side. This would usually result in my using a few choice four-letter words to describe the eBay seller, but I wasn’t particularly bothered this time. Remember those two unrepairable Macs I referred to earlier? They both had beautiful screens! So I was very happy to be able to put one of them to good use.
So time to find the fault. I decided to start with “lazy” diagnostics. This involves a quick inspection, with the hope that the problem will just pop out and bite you on the nose. It doesn’t always work this way, but when it does, it saves you from having to actually use your brain.
I pulled out the motherboard and had a look under the microscope. The reverse side (the side without the CPU) looked pretty clean, with only the smallest specks of corrosion – certainly nothing to worry about.
Next I flipped over to the front side and… bam! Up in the top right corner of the GPU was a nice little cluster of dusty, green corrosion. I reckon at least a 90% chance that this was our problem.
Under the microscope I could see at least half a dozen components that would need to be replaced. Thankfully I have rather a large collection of 820-2936 doner boards, so no real issue finding replacement components.
I fired up the hot air gun and started plucking off anything that looked a little ugly. Being so close to the GPU, I had to be very careful where I pointed the hot air to avoid doing any collateral damage. Once the ugly components were removed, I set to work cleaning up the corroded pads, ready for new parts.
After an my first cleaning attempt, there were still quite a few ugly pads, so I pulled out my scalpel and gently scraped off the corrosion from the worst pads, getting them ready for new solder. Thankfully I was able to restore all the pads, without any need to run wires.
With the pads cleaned up, I started the process of replacing the components. The layout was particularly confusing, so extra care was required to get the right items into the right place. It also didn’t help having quite a few purposefully empty pads nearby to confuse things.
The repair wasn’t pretty, but my testing showed that the continuity was restored and there were no shorts to ground. It would need a protective layer of conformal coating, but it should be as good as new.
After allowing the board to cool, I plugged in the fan and a power supply and… yippee! The fan starts spinning! I didn’t want to get my hopes up though, as a spinning fan is is only the first of many tests.
I cleaned the board in the ultrasonic, gave it an alcohol bath, then while I waited for it to dry in the oven, I replaced the cracked screen with a spare.
After putting the whole thing back together, I noticed that the keyboard backlight wasn’t working. I injected some voltage into the backlight, and it worked fine, so the problem was definitely on the logic board somewhere. I started looking around the LED driver, U5850. I checked the voltage on all the pins, then noticed something wasn’t quite right with the L5850 inductor. I double-checked my readings on one of my other boards, and it definitely appeared that the inductor was faulty, so I replaced it from one of my donors. After restarting, the keyboard backlight started working perfectly.
Initial testing showed the hard drive as failing, so I replaced it with a new one.
After a good clean, this laptop came up looking a million bucks. The battery was in great condition, but with a new hard drive, charger and screen, it certainly won’t be one of the most profitable repairs. Fingers crossed it receives a good sale price, so stay tuned for the results of the sale!