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By Penryn MacBook, I'm assuming you're talking about a white non-unibody A1181 model.
When a machine has no backlight but you can see a faint image, it can be the screen itself, the inverter, the inverter cable, or the logic board. It's not usually the logic board or the inverter, and between the screen and the inverter cable, it's more often the screen. If the light comes on or flickers when you move the screen up and down, that's a giveaway that the inverter cable is being crimped in the hinge and needs to be replaced. Otherwise, in your case, I'd replace the inverter cable first, first of all because it's the cheaper part, and also because it connects to the logic board near the upper-left corner of the keyboard, which is where you stated the liquid damage occurred, so that might be a hint that the inverter cable is at fault.
Before replacing parts you might also just try re-seating the inverter cable on the logic board side, and also cleaning up any visible liquid damage corrosion with q-tips and 90% rubbing alcohol. Sometimes that works wonders -- get the corrosion out of the way, re-seat the cable (and clean the cable-end too), let it dry, and who knows, that might restore your backlight. If not, try replacing the cable. Make sure to get the right one, because there are 3-wall and 4-wall inverter cables for the A1181. They are about $20-$30 on eBay.
Also, and this is a longshot, but sometimes people think they have a bad backlight, but really the screen brightness is all the way down. To test for this, reset the PRAM, which resets the screen brightness to the default level. If resetting the PRAM causes the backlight to appear, then there really was no backlight issue at all, and someone just accidentally turned down the brightness. It happens all the time on iBooks, and once in a while on MacBooks.
Anyway good luck, and let me know how it turns out!
John
Do you agree with those steps? What should I do first if cleaning it doesn't work? What is the best step?
Thanks again.
- Taylor
Anyway, the first thing to do is determine whether or not you see a faint image on the screen. You can shine a flashlight through the Apple symbol from behind. If the screen is dark but you see a faint image, then you've confirmed you have no backlight. (If you don't see anything at all, that's a whole different ball of wax.) I'd move the screen up and down like I mentioned to determine whether or not the screen lights up or flickers. Next I'd reset the PRAM -- if that fixes it, you don't even need to go inside the machine.
The next step is to pop the top, clean corrosion with alcohol, clean and re-seat the inverter cable connectors, let it dry, and see what happens when you power on again. Keep in mind you don't have to put the machine all the way back together to power it on -- you can have the topcase connected, but still loose.
If none of that helps, the next step is replacing the inverter cable.
Another useful reset is the PMU/SMC, which you can do by holding down the power button for about 10 seconds while the computer is off but connected to AC power. Basically keep it held in until you see the sleep light flicker, and you hear a loud solid tone.
By the way, I was able to fix the other guys computer with your advice. You the man!!
By the way, if you like the site, tell your friends about it! :-) I'd love to get more traffic on here, and even have other people answering questions. Growth has been slow but steady...at some point it'll get there!
I will keep you posted on this one though come Friday
Turned it on, got the chime but no picture. I then turned it off and reset the PRAM, got both chimes after 20ish seconds then let go of the keys and still no picture. I also tried to reset the PMU/SMC and still nothing.
My next thing I am going to do is hook it up to an external monitor and see if I get anything. If it works fine, I know its not the logic board.
Agree with me so far? What would you do after the external monitor testing?
What should be my gameplan? Keep in mind I have another MacBook penryn that needs a new logic board but everything else works (LCD, inverter, etc.). I need to fix this one ASAP. Can I take parts from the other one to make this one work??
Let me know and thanks as always!
-Taylor
Or, you can put this board into the other machine (again, assuming the inverter cable is the correct type), since you know that entire screen assembly works. If that works 100%, then you have ruled out the board, and you know something in the original screen assembly is bad (inverter cable, inverter, or screen). But at that point you'd still have to start replacing parts to get the original screen assembly working.
Sorry for confusing you.
I currently have 2 Macbook's on me, both black and both 2.4 GHZ Penryn Models. I also have an extra 820-2279A logic board, 2.4 GHZ that doesn't work once it hits the OS, but it does boot (perfect for testing display assembly's because I will be able to see the bright white screen with the Apple logo at startup).
Let me un-confuse you:
1st One: My cousins laptop that got FedEx to me, this is the one with the liquid damage on the top left of the keyboard. This one was hooked up to an external monitor and it worked just fine.
2nd One: This is the other thread. This one has already been diagnosed, it needs a new motherboard.
OKAY...on to the good and bad news with the 1st one (this thread). So, I took out the motherboard and put it in the 2nd one's case (i know this LCD assembly works, so I was testing the motherboard of the 1st one to narrow the problem down). I got a feint image. Not good because this LCD assembly works on different logic boards. I then took an OLD logic board (referred to at the top) , 820-2279A, and put it in the 1st one case (I wanted to see if the display assembly work so I could narrow it down even further.) I got a bright white screen with an Apple logo. WOW.
So, the problem with the 1st one is the logic board. Even though I am able to hook the Macbook up to an external monitor, browse the internet, listen to music, write documents, connect to wifi, etc.
My question to you is...How can that be??
Is it possible for the backlight connecter on the logic board to be "fried" and not affect the rest of the logic board?
So, what I just did is, took the logic board out and scrubbed with 90% alcohol and q-tips around the backlight connector on the logic board. I will let it dry overnight and test it in the morning.
What are your thoughts? I can't believe everything on the logic board can be working but the backlight connector...so annoying.
Would love to hear your input.
Thanks
-Taylor
I think you mentioned you've tried the PRAM and SMC/PMU resets on this machine, but if not, try those, because occasionally like I mentioned the screen brightness is simply all the way down, giving the appearance of a bad backlight. Also, when the machine is booted up, you might want to try hitting F2 repeatedly to increase the brightness as well, just to see.
Beyond that, I would specifically try to clean out the inverter connector, and possibly try a different inverter cable if it's not too much of a pain, but beyond that, yeah, it sounds like you have a bad board.
http://www.ifixit.com/Answers/View/16492/Backlight+dead+and+something+fried+on+the+mainboard+-+Please+help!
You may want to see if your board has the same or similar markings as this one, and if you can bridge the connection to restore the backlight, as this person did.