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Model A1311 / Mid 2011 / 2.5 & 2.7 GHz Core i5 or 2.8 GHz Core i7 Processor

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Display damaged. Unable to use external monitor to access iMac

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Found an damaged iMac A1311-2428. The student mentioned it had ‘issues’ before the screen was ‘damaged’ before driving off. When I power it on. It goes through boot up fine with boot chime and display lighting up… even the section of backlight BUT nothing on the display.

I picked up a Mini Display Port to HDMI cable. I tried a monitor with DVI to HDMI adapter and TV with no luck. I’m using a standard windows USB keyboard and mouse to try to switch to external monitor. No luck.

I’m trying to see if what errors exist before sinking money into new LCD and front glass plate. If I can get it back working … bonus. Else it was worth the time trying. Like I can do any worse to it as it is now. Thanks in advance.

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Likely the GPU failed, people tended to push these systems beyond what they where designed to support with heavy graphics. This is what’s required to fix this iMac Intel 21.5" EMC 2428 GPU Card Replacement beyond the replacement display which doesn’t make this worth to fix. Sorry ;-{

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Ouch. What I feared might be the case, does that means that I can't use external monitor without the GPU?


@michaeleh - That changes things a bit! You'll Still need a new display panel as yours is broken. But you'll then need a controller board to replace the logic board if you want to convert it to an external monitor.

Basically, you are just using the shell, the LCD panel and the power supply everything else is taken out.

I'm still not sure given the costs is worth it.


@danj It depends on whither the cost of repair (if I do it myself) is less than half the cost of buying the same or new mac then it *might* be worth the trouble _IF_ there isn't any other underlying problems. That is main reason to try to get into the system somehow to see what else is wrong. If a bad GPU is the only reason why external monitor won't work then it's an obvious fix. Else replacing the GPU and LCD would be pointless. If there is some other component or software that is preventing external monitor, it gets dicey. Do I continue or sell it as a parts machine. I'm trying pinpoint the root problem then rest is just fix it up to working computer.


@michaeleh - Hold on here! Now you've changed things again!

A working iMac is replacing the GPU. Converting the display into an external display replaces the logic board with a 3rd party controller board (A for B).

The GPU feeds the video to both internally and external displays. So it's clear the GPU has failed.

You stated you get a boot up chime so the logic board its self is working!


@danj Thanks for making things clear. I'm not interested gutting an iMac into a monitor. It wouldn't really make sense when I can go out and buy a cheap 21" monitor anywhere. I'm just trying to rule out anything else before proceeding.

In another thread, they mention the diagnostic LEDs and trying to peek through bottom grilling to the right of ram slots, it showing all 4 LEDS lit. 3 is display is talking to the board. The 4th is lit which some posts saying this temperature error. Another saying the video is okay.

Boots up with a black screen

Forgive me if it seems like I trying to get out changing the GPU. I'm trying to diagnose any other issues that also might also be not obvious. Usually, people would change the LCD then still get black screen then change the GPU only to find something else wrong. I'm trying to get to the root cause so I can decide IF I'm going to fix it at all.


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