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1 2011 iMac no backlight- Logic board?
Hi all,
I have a mid 2011 21.5" iMac and there is no backlight on the LCD. If I shine a torch on the screen I can see all the icons faintly. I can see also see everything on an external monitor clearly.
I thought the issue might be with the LED Backlight driver board so I replaced that and no difference, I can still only see the icons faintly with a torch.
I then tried another LCD and same result. Icons only visible faintly under a torch.
Now I'm starting to wonder, is it a faulty logic board? I read this post here Mac: Signs of a Bad Logic Board (scroll down to Display and Graphics Problems) It's also not the GPU hence as I mentioned the I can see everything on an external monitor.
Does this look like a logic board issue? Everything I've done is leading me to this conclusion.
P.S. All the diagnostic indicator lights go including the LCD communication one. So the iMac is detecting the screen.
Please let me know if you have some advise.
Cheers.
973 
5条评论
The Techwalla article is very top level and generic.
A laptop internal display often uses one cable connection and one logic board so everything is on it.
In a desktop (iMac) the display being larger requires much more power to light up the larger LCD panels backlights and the cables are independent between the power and display signal cables. In this iMac the backlight logic is held within an independent assembly as well (LED backlight driver)
You are on the right path the backlight is the issue not the main logic board.
由 Dan 完成的
Hi @danj. I tested it with a Ohm meter and I got 10v going into the LED backlight driver on all 3 drivers I have. I also got voltage coming out of the cable that connects to the backlight driver.
I have tried everything. I put a new power supply in from an identical model, 3 different backlight drivers and now after reading what I saw in the link leaves me to believe it’s the logic board.
What are your thoughts?
由 Jacob Milly 完成的
I think you'll need to find the schematics to see for your self. The issue is still the Power supply to LED driver and then the display its self. Something is just not right here the voltage you measured is low it should be 12 volts and 24 volts if I remember correctly.
It sounds like you have a second system is that correct?
由 Dan 完成的
@danj Yes that’s correct I do have another system of the same model. The bizarre thing though is that I swapped the power supply’s, from the working one to the not working one and it didn’t even turn on! All I got was the one LED! So you think the voltage is wrong?
由 Jacob Milly 完成的
Post some really good pictures of your logic board with your QUESTION. that way we can see what you see. Post some extra ones from around the DP connectors 在已经存在的问题里加入图片
What voltage do you have on L9000?
由 oldturkey03 完成的