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Model A1312 / Mid 2010 / 3.2 GHz Core i3 or 2.8 & 3.6 GHz Core i5 or 2.93 GHz Core i7, ID iMac11,3

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27" iMac Mid 2010 screen goes blank

I have a 27” iMac Mid 2010 Core i7 2.93 GHz that has run well for many years.

Starting about 6 months ago the screen would go blank randomly. Putting the Mac to sleep and waking it up would bring the screen back. It important to note that only the back light would go out. I could see the screen image with a very bright light and the external Apple monitor was unaffected.

Over time it would happen more often and I noticed that lowering the brightness would allow the screen to stay on. I got to where the brightness can not go above 2 notches before the screen would black out.

I have tried to replace the inverter board (with a new on), the actual display with a use one as well as the Radeon HD 5750 graphics card with a used one.

None of these have helped. I have read every thread and each has had different solutions. I’m not sure what to try next.

Any thoughts?

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The only thing I can think of that could be a factor here is the SMC logic within the main logic board. I would run the onboard diagnostics to see if something pop’s. To run diagnostics reboot your system and press the D key to enter. Let us know if you get any errors.

I would also look at the thermals using a good monitoring app like TG Pro if you get the full version you can get logging which might help in identifying whats happening here.

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Thank you for your suggestions, Dan. The iMac showed no problems with the Apple Hardware Test. The TG Pro shows nothing unusual with the GPU temps. The screen will go blank when I turn the brightness past three squares in just a few seconds.

So iMac still runs fine with very low brightness on internal monitor and external Apple monitor unaffected.

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Did you get the full version? That has some added diagnostics which might help us hear.

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I did get the full version. The log show only normal events even when the screen goes blank. This problem seems to be the same even right ofter booting the iMac from sitting long enough to cool off. I do not think it is temp related. The best thread I have found refers to the LED light strips pulling too much current and tripping a protection circuit. Show below.

Backlight randomly turning off

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The display has two thermal sensors one within the T-CON board and a second on the panel its self. The LED strip is setup in banks I would have expected one or two banks going off. If the connector had failed this is when the display dims on its own. Here we have a full wink out which would more likely be the LED driver. TG Pro should have given you a clue, can you post the log file here so I can check it.

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dasgeek “lowering the brightness would allow the screen to stay on”  and since you’ve already changed your LED driver board,  changing your backlight strips should fix this issue.

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dasgeek zal eeuwig dankbaar zijn.
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