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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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Few vertical lines appear quickly then goes black

This happened after I cleaned my LED backlight board and my power supply.

Before I cleaned them up, my iMac kept dying if there was any 'heavy' graphics-related job. Now, that issue is fixed(which means that I can run some graphics-related programs), but I get a few vertical lines appearing for a split second then the screen goes black.

The strange part is that it runs okay when it's in the boot stage(when the Apple logo appears, or when it gets to the boot selector, etc), but it doesn't right after it runs its OS.

Edit: I've also upgraded my CPU from i3 550 to i7 860.

Update (07/11/23)

@danj Great news! The graphics card is alive. Check the picture here:

Block Image

Now I wonder what's the problem... Maybe the LED board? I mean since it also controls the display's vsync timing so...

Edit: I tried booting to macOS Recovery and realized that the display works(without any lines, just as clear as it should be) if the external display is plugged in and breaks when I unplug it. The funny thing is that I can replug it to revive the iMac display.

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iMac’s leverage the Intel CPU’s graphics engine at startup. Then, the MXM graphics board GPU takes over.

So as an example if you restart your system using the Startup key options you can stay with the Intel graphics will still be active.

Sadly, it’s likely the system an MXM board needs some cleaning and replacing of it’s TIM both paste and pads.

I would install a good thermal management App like TG-Pro which I find is the best! As you need to see clearly what’s happening and boost the fans to help keep things cool.

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Does overheating cause vertical lines and etc? I'll try this but I don't think it's a thermal-related issue tho.


@helloyunho - yes overheating can cause this. But unless you see the systems thermal sensors you won’t know. The graphics board has its own cooler and fan. Even still the thermal paste and VRAM chips thermal pads lose there effectiveness with age.

Otherwise the display it’s self has issues.


So it's been about 3 months and it still doesn't work. What I did was:

1. Clean and reapply the thermal compound

2. Adjust the fan to spin based on GPU's temperature

Again, I think this is a hardware issue and not something fixable on the software side.


@helloyunho - What did TG-Pro tell you?

Without the data we can’t help you😩


@danj Sadly I use Linux on my iMac, so what I did was installing mbpfan kernel module(and yes it works on iMac as well).


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Helloyunho sarà eternamente grato.
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