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Dead display = broken LVDS cable or SMC part?

Hello!

On my friend's late 2010 MacBook Air the screen is completely dead. No video, no backlight. When connecting to an external monitor, everything shows up fine, exept for the internal display not showing up in the system info panel. So at least the graphics chip is not blown up.

Moreover, the hinges seem a bit too worn out/loosened so that when having the lid open at a small angle it closes by its own weight, when it more likely should stick in that position...in my view.

My question now is: is it more likely that the display is dead due to

1) a broken LVDS cable due to the seemingly "heavy" use on the hinges or

2) some other smc component on the logicboard fried?

If so: how to test the components on the board with a multimeter? I have one here, but only for testing batteries and checking currents, but other uses are beyond my knowledge as I'm not an electrician, but an excellent industrial-/fine-mechanic, so I'm not worried about having to do some fiddly work with my fingers :D

But at least I found the exact positions of the parts in question marked on some photographs I found here in the support forum. The only knowledge missing on my side is the process of how to test those for functionality?

Do the display background LEDs get their power through the same lvds cable or from the cables on the other hinge?

I hope, you guys can help me find out, what is causing the dead display and a feasable way to maybe get it back to work. I just don't want to pry open the display assembly and change the display unit/LVDS cable for nothing, just to find out, that there are some parts on the logic board burned to dust, making the complex process of opening the display assembly useless.

Thanks a lot in advance!

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killahman, "I just don't want to pry open the display assembly and change the display unit/LVDS cable for nothing, just to find out, that there are some parts on the logic board burned to dust, making the complex process of opening the display assembly useless." It may be a bit of work, but most certainly easier than anything on the logic board. If you do want to check the components on the board, I suggest to check the fuse for continuity and check the Mosfet's to make sure that they are okay. If all of that checks out, then you are back to square one, which is your LVDS cable, connector, LCD. Hope this helps, good luck.

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Ok, so buzzing out the fuse gives a nice and clean "beep" for conductivity. How do I test the other two marked components? Q9706 does not beep, but shows a 430 shown on the display on diode/continuity mode selected. Does that make any sense to you or is it the wrong testing method in that case? Sorry for being a complete electronics layman...

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killahman, check this site for a "quick and dirty" test http://www.utm.edu/staff/leeb/mostest.ht...

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Alright, but the MOSFET on the board has, as far as I can see, and as long as I have identified the right part, six pins, making the above instructions for testing a three pin MOSFET obsolete, or doesn't it? And what about that red/brownish part q9706? How do I test that one? Doesn't seem like a MOSFET to me at all, due to the lack of three pins, or am I completely wrong on this?

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not easy to check those with a normal multimeter:-) that is why I attached that part of the schematic. It does show the pinout for proper testing. On the 4 contacts you should have 12.4V, if you get that, you could be reasonable sure it is working.

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Ok, got that. I even realized that I misinterpreted the arrows. I thought one was pointing on the red/brownish part, instead the MOSFET below it is meant. So, now that I know the right parts to test I still have a hard time figuring out which real pins match the ones from the circuit schematics. And to get a 12.6V reading that implies having to test the MacBook alive, with the battery connected, doesn't it? So my fear lies in short circuiting the wrong pins, as the schematics only give me a rough hint that there are four pin outs carrying voltage, alas, there are two more pins to mess around with :) But as I said: I am an electronics layman. I am willing to learn, but any detailed help on 6pin MOSFET testing on Late 2010 MacBook Air led backlight circuitry would be appreciated :) Thanks for your patience, guys!

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The easiest and safest way to fix this is to replace the entire lid assembly. That way you resolve most of your concerns. Follow this IFIXIT guide it is similar to your systems setup: MacBook Air 11" Mid 2011 Display Assembly Replacement.

The only issue left is if the fuse links are blown on the main logic board. The fuse links are small SMT devices near the display connector with a dot on them. But, lets not worry about them quite yet.

Can you shine a flashlight though the lids Apple logo and see any faint image on the display? Are you able to see any glow from the lid when you turn up the brightness? Let us know what you do see as that can help nail down things here.

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Unfortunately the whole display is dead, meaning the panel itself and backlight. Thus, shining a bright light through the apple logo does not reveal anything. And that's not, because of the panel displaying a white area in that spot, as I tried placing different colored elements in that particular area while I had an external display attached.

That's why I came to the conclusion that obviously the lvds cable could be the root of evil. And to spare the expensive costs of replacing the entire lid, which is around 300 quid around here in Germany, I would more likely only want to replace the display/cable if that could bring the viewing experience back to life, so to say :) I'm not worried about the somewhat time consuming and fiddly work, as I've replaced several 1st generation mb air screens, which from the pictures seems like a similar process...

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killahman will be eternally grateful.
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