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LCD screen brightness too dim after repair of iMac 20"

After following the instructions to replace my hard drive (iMac Intel 20" EMC 2105 and 2118 Hard Drive Replacement), right after I finished the repair and started using my iMac again, the screen brightness is more dim (even when adjusted to full brightness) than before.

Could it be that I didn't attach any of the connectors properly? Or any other advice someone could give?

I have already reset the SMC and PRAM, which didn't have any effect. The brightness control is at maximum setting.

Many thanks in advance.

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when you say it is dimmer than before, is the backlight coming on at all, or is it not on? because they would be very different. If you can adjust the brightness and it is visibly illuminated, just dim, then there is a fault with the machine, because everything is connected fine. Whereas, if you cannot see a backlight but can see the image faintly (either with natural light shining on the screen or looking with a torch) then it is most likely the connection of the inverter board that is not seated properly.

either way you will most likely need to open the machine back up again. I'd initially check all the connections, then if it doesn't help, you will need to track the fault down a bit further.

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Hi Jon, thanks for your reply.

Yes, the backlight turns on. I can use the brightness controls to change the brightness just fine, it's just that the maximum brightness seems to be dimmer than before.

In fact I was looking more closely now: when I turn on the machine, or when I wake it up from sleep, I notice that the brightness goes up for a second or less, and it appears to be the 'original' full brightness, and after that it jumps to the dimmer brightness I described.

Would that be a hardware issue? I.e. a cable connection that's loose or bad; or could it be a software issue, given the fact that it does go to full brightness very very briefly?

Kind regards.

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Try resetting the PRAM (hold down the keys Apple-Alt-P-R then press the power button. the machine will chime ones, then will restart and chime again. after the second chime you can release the keys)

after that you will need to open the machine again. it could be a faulty inverter board, or just a sign that the LCDs backlight is going. It is normal for the backlight to seem slightly different during the initialisation stage before its started, but if its considerably different, it would be a fault with the machine... Its less likely to be a fault with the OS, but it could be to do with the settings within the OS, which is why the PRAM reset will help, as it sets the display settings back to its original brightness, etc...

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I am having the same issue. Anything work for you?

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Hi Cory, I have tried all of the above advice, except the part about re-opening my iMac; I'm a little reluctant to do it again (as it took me quite a while last time and I'm not sure what to do anyway once it's open...)

In any case, so far no fix. Did you encounter exactly the same? I.e. did it happen after you had opened the iMac for another repair?

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I too have tried all of the advice. My screen is only slightly dimmer than normal, but I do notice the full brightness immediately after waking from sleep, but then less than a second later, it becomes more dim. It happened after I had it open for another repair. I haven't opened it again, but probably will when I have the time. The screen removal part was pretty simple, so I do not think it would be too difficult to open it to check the connections, however, I do not think that this will fix the problem. I will let you know though either way.

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Cory and Simon, I am having the same issue. I'm on an Early 2008 iMac. Any chance you figured out a way to resolve this.

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Matt - For future reference you posted a Question in the place where only Answers belong. Please use the add comment link to the appropriate Answer, Question or create your own original Question.

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http://hackaday.com/2014/01/21/finding-t...

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