Released June 2012, Model A1278. Intel processor with Turbo Boost, Up to 512 MB DDR5 Video RAM

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Liquid damaged laptop; power problems after fix

So I received a friend's liquid damaged laptop and offered to try and fix it. Apple wanted to replace the logic board which wasn't a cost-effective option so my friend decided not to have it fixed. I offered to take a look and determined that having the keyboard and trackpad connected on startup was the cause of the panics.

Bought a new trackpad / upper case and installed it. The computer runs well now but there are a few quirks:

  1. The fan always runs on high
  2. The computer tells me there is "no battery available" even when the MagSafe is disconnected and it's clearly running off the battery (it even says "power source battery")
  3. The MagSafe charger light doesn't turn on when plugged in

2 and 3 sound like DC in board problems but I'd like to do some more troubleshooting first to make sure this is the case (sometimes old batteries report as not existing and sometimes the charging light doesn't turn on for whatever reason). What troubleshooting steps can I take to figure out these problems?


New symptoms: the computer won't go to sleep by either the apple menu nor closing the lid. The fan continues to spin and any activity will wake the screen to the password screen. I don't know if this is related to any of the above points or is useful.


When taking apart the computer again to continue troubleshooting I re-discovered something that may be corrosion on the left side of the logic board:

Block Image

I've got an unused toothbrush and some 99% isopropyl alcohol, should I start cleaning?


I had taken off the logic board again in order to clean it when I figured out where and how to use the multimeter (somewhat). So I wiggled the DC in board connector and put the thing back together. I tried booting it up but nothing happened! So I plugged it in and - wonder of wonders - the MagSafe light comes on and the computer boots!

I was able to read "1." off the 2 DCV setting (so 2 direct current volts?) for pin 14 of U7000, which seems to be correct. Also read "1." off pin 12.

Considering that one of the symptoms has changed, I'm going to see what other symptoms might remain.

Final edit

All symptoms are gone. I'm going to chalk it up to the wiggling the DC in board connector and call it good. It's been a wild ride and I've learned a bit about the circuitry in computers. Thanks for the help!

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So 2012 model, this means 820-3115 board. First homework is to find ASD 3S150 or 3S155. Yes this will require going to illegitimate websites because Apple are !$$&*! that keep this from you on purpose, but what are you going to do. People still buy their products in droves so they can do whatever the &&^& they want. It will tell you what sensor is at fault causing the fan to always run high. You need to know this or else you'll just be guessing.

On battery recognition, the SMC data line that communicates with the battery also communicates with the BIL, the battery indicator/sleep sensor on smbus_smc_5_g3_scl and smbus_smc_5_g3_sda. Disconnect that and see if it fixes anything.

See if R5280 and R5281 are present on the board or ripped off. If they are present, see if there is pulsing on the smbus_smc_5_g3_scl and smbus_smc_5_g3_sda sides of the resistors. It should look like 8:39 from this video on an oscilloscope. It should peak at 3.42v and go down to 0 to make waves.

On charger, try DC in board but also see if SMC_BC_ACOK on pin 14 of U7000 is high. Anything lower than 2v and something is &&^&@@ up with U7000. If you see that 2-3v on U7000 pin 12, move onto U6901 and see if it makes it to the input of the logic gate at pins 1 and 2, and see if this is sending PP3V42_G3H to U6900 on pin 4 of U6901.

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Thank you for the assistance, but this is a little bit over my head at the moment, I'm going to need some clarification.

I've never done capacitor level repair nor do I have an oscilloscope (I may have operated one once or twice...) Is there some other tool I can use to check it?

I don't have a blueprint or anything like that to know which circuits you are referring to either, do you know of a link to that?


Ok screw the oscilloscope part then.

Take multimeter, set to voltage mode, put black probe on a screwhole, and red probe on pin 14 of U7000. In terms of schematics/boardviews that is your journey to find someone who has them for 820-3115 board, distributing them is illegal so all I am going to do is tell you what to look for and measure once you find the schematic/boardview.


and unplug the battery level indicator, see if this improves anything.


I'm working on acquiring those other things, but in the meanwhile I unplugged the battery level indicator -- unfortunately it didn't fix anything. I did "re-find" some corrosion that had skipped my mind when making the post, and I've added an image as an edit above. Should I try cleaning that and see if that helps? (in the meanwhile, I'll have to borrow a multimeter from work when I get the chance, but I'm not sure of how to interpret those schematics yet; hopefully fixing the corrosion will improve things?)


Holy $@$*. Ultrasonic this board before plugging in any power again. Buy a Fluke 15B it will pay for itself after the first job.


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