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Model A1419 / Late 2012 / 2.9 & 3.2 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac13,2

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Black screen but can see icons with torch

Hi. I seem to be spending hours trying to search for the answer to this, but I'm going around in circles. I hope you can help.

I have an a1419 27 inch late 2012 (I think)

The screen is black, but I can see the icons with a torch. I can link my thunderbolt or external screen to get an image, this is fine. I tried replacement panel, no good. Now I am trying a new display cable, but the costs of trial and error are mounting.

What could be wrong? I am grounded when working on it. If it's the backlight what do I do on this model, as I can see they are all "slightly" different inside. I've read about fuses, and controllers, but not much info about the a1419 out there I'm stuck....

Thanks for helping

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It really does sound like a backlight problem, in which case is out of my league.

The only other thing I can think of is if, somehow, the brightness settings were set to minimum (but I really don't think they even can go that low on the iMacs). To avoid possible unnecessary part replacement and hazzle, you should make sure by using the torch to help you navigate to System Preferences and then click Displays and make sure the brightness slider is to the far right. Also there may be a checkbox there that says "Automatically Adjust Brightness" that I'd leave unchecked in this case. I know this seems an unlikely cause since an external monitor displays a clear image, but one can never be too thorough. :)

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Thanks for your help, but I tried this and didn't work. Anyone else -scratch head time.......

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If it's the backlight, then the problem is most likely in the circuits and it's time to bring out the multimeter and the understanding of circuits and their components.

You could start out first by eyeballing. Check for bloated, popped or otherwise disfigured capacitors (google images may help you know what to look for). Although replacing a faulty one is often only half the problem as a popped one is often just a symptom rather than the cause. You need a soldering iron to replace these.

Now for the fuse, those are normally marked with an upper case F followed by a low number. Also they are normally marked further with a rectangle border around the component. Lastly, they are located very early on the board where the power comes in as their purpose is to break to protect the rest of the components in the circuit in case of a bad voltage.

Now if the fuse and capacitors are healthy I recommend consulting an expert as the next steps require measuring and knowing what voltages should be where (advanced repair manual for this model perhaps), which does require the circuit to be live. This is dangerous as there's a high risk of electric shock and also a high chance of shorting out the circuit with the probes causing even worse problems if one is not extremely careful.

Good luck!

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Thanks for this, I will get the board out and have a look. :)

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Just remember to be extremely careful around live circuits, even in the low voltage parts - accidentally short between two pins of a sensitive component like an IC and it dies.

Good luck! :)

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Really sounds like a backlight problem. Also have you tried turning the screen brightness up and down. Its the f2 and f3 keys on the keyboard. Does hitting these make a difference and can you see the icon on the screen saying the brightness is going up and down using the torch to see it? If this doesnt change anything its probably the backlight.

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Hi. Yes tried turning up nd down via the F keys -no difference. So if it as I suspected the backlight, what do I do. Is it a board, fuse....cable? Ho can I test for this. I can't seem to find information on this. What I could do with is a list of possibilities, then if I can see via a video someone doing a tear down or investigation, I will follow it. I just need to know what to do next/what to check? I don't think this model has a separate backlight board (amateur talking.... :) but a direction of things to look at next would be really great1 Thanks again for your help!

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Not sure. Theres someone here not sure who it is who would know better then I

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Possibly a fuse. Look for a fuse and check continuity. If there is none. Its broken and you need to replace it.

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Where is it, and is it labeled with anything? I know some machines have a white dot on top, but I couldn't seen one when I checked yesterday, the two possibilities are 1. I missed it, or 2. It is under the Aluminium casing (as i have not stripped the logic board out yet. Do you know or have you a schematic? :)

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No clue. I dont work on these. I just help people solve common issues.

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