Disassembled and reassembled, now my display shows weird colours

I spilled some liquid on my late 2011 MBP keyboard around the arrow keys a few days ago. Immediately powered it off, flipped it upside down, left it like that to drip out for about 5 minutes before I wiped the keyboard and then removed the back cover to check for internal leaks. While at it I used a can of compressed air to clean out the last year's accumulation of dust.

Wanting to make sure there were no signs of liquid around the keyboard on the inside I followed ifixit's guide to removing the outer case up to the point where you remove the expresscard cage but got stuck with some screws that refused to turn, so I used the compressed air to blow as much liquid out of the keyboard as possible (while still upside-down) and then decided to leave the laptop open and upside-down for two days to dry out. The logic board was completely removed during this period and there wasn't a drop of liquid on it or visible anywhere inside the laptop.

I re-assembled it following the instructions carefully, and everything but the left and right arrow keys works great... except for my display. The first time I turned it on there were tiny vertical lines on the grey startup screen and all blacks were bright red, so I backed up my harddrive, did a PRAM and SMC reset with no luck, then opened it back up and removed and re-inserted the display cable. Now blacks are black again, but the display still has vertical lines on grey and generally weird colours in addition to some colours flickering. I hooked up an external display and there are no issues on that screen, just the laptop's.

Photos of the issue

My laptop was fixed by Apple previously as part of the repair program due to similar display issues (vertical grey and pink lines on startup) which I was under the impression meant it got a new logic board. Unrelated but I've also upgraded the RAM (installed 2012) and a new SSHD (installed 2016) myself.

Any ideas for what I did wrong to cause this and what I can do to fix it?

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The particular video defects you describe are usually a result of a bad connection between the video cable and the board. The first thing to try is to re-seat the video cable as securely as you possibly can, and that often resolves the problem. Make sure the cable is fully seated into the connector, and that the clasp is all the way down. You can also clean the video connector and the socket, but be very careful. If none of that does it, it's generally the video cable itself (not the board or the screen panel).

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After the two attempts to re-seat the cable as mentioned in my original post failed, I tried a third time just now and my display was out completely on startup; no backlight, nothing. I panicked a little but opened it back up and removed and re-connected the cable a fourth time and lo and behold, my screen is back to 100% normal now!

I guess it's just a really finicky connection, so I'll be careful in the future and try not to jostle it when doing routine cleanings or fixing any other issues.

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Since you get good video on an external screen it's not a bad motherboard. Either your screen's display drivers are having issues, the display connector on the motherboard is damaged, or the display cable is damaged.

Likely not the screen display drivers; they usually go bad only when the computer has been dropped, banged around, or had a weight set on the (closed) screen. So I'll go with either a bad display cable or display connector. Pull out your magnifying glass and examine the display connector on the motherboard for damage or dirt/moisture residue/corrosion. Clean it with some >91% isopropyl and let it dry. Check the display connector as well for similar signs of damage; GENTLY tug the wires to make sure they're all still attached to the harness.

PS: For future reference, NEVER use compressed air to blow moisture "out" of electronics. While you may get some or even most of it, you'll never get all of it, and there's an almost certain opportunity for some of that moisture to get blown into areas where it can create a short circuit.

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Thanks for the advice!

What's the best solution if there's a decent quantity of liquid in the keyboard and you can't physically remove the keyboard? That was my main goal, but some firmly stuck screws prevented me from being able to remove it from the case. Since the liquid was toward one end and the keyboard backlight on this model adheres to the case most of the way around the keyboard I figured my best chance at getting things dry was to blow it out where it would do the least harm (toward the arrow keys at the bottom corner of the keyboard, by the optical drive which I never use anyway). Judging from the amount that blew out of the keyboard, just letting it dry upside-down wouldn't have removed as much liquid.

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Keep in mind you're not really asking for the BEST solution, but rather the BEST solution that doesn't involve the PROPER solution (which is replacing the keyboard). I'm not being sarcastic, I'm just making sure we're on the same page.

:-) That being the case, I would probably disconnect the battery, suspend/prop it so the keyboard was fully upside-down, fill a spray bottle with distilled water, and gently spray up into the keys to wash everything out as good as I possibly could (being careful not to spray TOO hard and get more liquid inside). Then I'd probably repeat the process with 99% isopropyl alcohol, then I'd put it inside of a vacuum dehydrator until no more moisture came out.

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Definitely on the same page :) If I could get those sticky screws out I would absolutely replace the keyboard.

Great second-best-option cleaning advice, thanks! I never thought of spraying *more* liquid into the keyboard, but I can see how using something like distilled water or isopropyl alcohol to wash out tea while it's upside-down would be better than the tea remaining in the keyboard and drying up.

Do you think if I try this days later it might restore the left and right arrow keys that aren't functioning by clearing out any dried residue from the tea (which contained milk), or are they likely too far gone? My space bar and b/n/m keys are also a bit sticky but at least still functional.

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Maybe. Keyboards are electronically very simple devices and under normal circumstances nonfunctional keys are almost always due to dirt on the contact points. A tea w/milk spill isn't a normal circumstance.

The issue is, if the residue is simply blocking the connection between the little conductor inside the rubber cup that's under the key then the safest thing to do would be to pop off the key, remove the cup, clean all the contacts with isopropyl and a Q-Tip, then reassemble. This does run the risk of breaking the delicate scissor mechanism under the key so it's up to you if you want to take that risk. (You can buy replacement individual keys online.)

But if the tea/milk got inside the keyboard (beyond the key cap area) and caused a short, then cleaning it as I described earlier is your best bet — but it IS a bet, a gamble, not a guarantee. The water and isopropyl would need to travel to the same place as the tea/milk and thin it out enough to break that connection before evaporating.

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Honestly, I've found that to not be true of keyboards at all -- 95% of keyboards with bad keys have gotten fried and are unrepairable, and simply need to be replaced. The "alcohol and a q-tip" thing that is always suggested sounds nice, but it just doesn't help the vast majority of the time. Maybe 5% of keyboard issues are due to an obstruction, or the scissor mechanism having come apart, but pretty much everything else requires a keyboard replacement. And even if alcohol did "fix" it, you run a very high risk of the flaky behavior returning before long.

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