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Mid 2012 model, A1278 / 2.5 GHz i5 or 2.9 GHz i7 processor.

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Dark screen, backlight working

Hi all,

Display flickered and went dark while using it. Backlight is working, and external screen is working through another mac connected by thunderbolt; everything else also working fine via external mac.

Have reset NVRAM and SMC to no avail.

Also tried reconnecting LCD cable (but only on logic board side - haven't tried doing screen side yet) - this made a small difference as display worked on startup for about 10 seconds, before flickering and going dark again.

Another forum suggested it may be the logic board? I am fishing for other tips and tricks or diagnosis steps I can try first as this is an expensive replacement for a 2nd hand (refurbished) machine. I live remotely and difficult to get to a tech.

Is there a layman's way to test the logic board? Any advice much appreciated.

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Connecting two Macs via Thunderbolt is not the same as an external display (screen sharing or via Target Disk Mode). All you're doing is sharing the screen or accessing the drive, not testing the systems ability to push a screen natively. Even still it's a good sign!

You’ll need to try a VGA or HDMI connected external display that way we know the GPU logic is OK and we only need to worry about the internal display.

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Thank you Dan. Was just following your advice and setting up the faulty MBP with drivers for a usb > vga adaptor (it's the only option I have for an external monitor). When I started the faulty machine, the screen went from black to faded / patchy white. I then restarted as it was moving very slowly and - the internal display screen is back! From forums I'm not getting my hopes up too much, and still looking to diagnose what's going on, but wondering if that sheds any light on possible problems?

Don't know if this is relevant, but we have had a sudden cold snap (cold for the tropics - 7 - 20 Celsius rather than 25-35) and I'm wondering if temp could play a part?

Many thanks for your time

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In a way it can, temp swings in a humid environment (tropics) can allow condensation to form! I would recommend you try to control humidity where you either use or store your system.

I do think you'll need to do a good inspection of the logic board and it may need some cleaning.

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Great, thanks so much. Will do a clean or maybe get a tech to inspect when I'm next in town. All the best.

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Hi Dan, if you are still out there...internal display is working intermittently - sometimes coming on again after a restart and working perfectly for hours, then after a rest and reboot display is gone again. However the external display (via vga) is fine. So you earlier implied that this would mean GPU is ok - does this mean that I am looking for display cable/ inverter or related issues, or is logic board still a possibility? thanks in advance

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OK, thats good info! Now get a flashlight and when the screen goes dark on its own place the flash light on the screen at a angle (about 20 degrees) are you able to see the faint images of your desktop and its Icons? If you are then we know the backlight logic for the display is in trouble. If there is no image then it's a loose cable or bad solder joint in the LVDS connection.

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