Late 2009 iMac. Screen flickering, then blacking out.

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Hi, sorry if this is a frequently asked question and everybody is tired of it. But I'm having problems with the screen on my iMac 3.06 GHz Intel Core 2 Duo, 4GB running OS X version 10.9.3. I bought it late 2009 and it has never had a problem until early this year. At first the screen flickered slightly every so often dimming the brightness. Now it has gotten worse, it does this, then it goes completely black. I use it mostly for music and it blacks out sometimes when I am playing on my keyboard, after it blacks out I can still play and listen to what ever video, music is playing. I went into the apple store and the service was rubbish, they told me I would have to pay £50 logistics and then the cost of what ever the problem is etc. Then I contacted a local computer repairs shop and they told me it was most likely a motherboard problem, but I know that is bull****. Can anyone help me to diagnose the problem? So I can either fix it myself, or prevent myself from getting ripped of by some technician.
 
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2019 iMac 27"; 2020 M1 MacBook Air; macOS up-to-date... always.
Actually it does sound like a motherboard problem. Try running the Apple Hardware Test to see what it says. And update to 10.9.4.
 
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If you are really lucky, this may prove to be something as simple as a loose cable connecting the display to the GPU, or maybe a faulty cable. You can look over iFixit's repair guides to see if it's something you want to tackle yourself. Opening up these iMacs is not for the faint of heart though... it is very easy to damage a cable if you aren't extremely careful (I damaged one myself).
 
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I ran the extended hardware test, it said "No trouble found". I'm not sure if that is a good sign or not. Normally I would think yes, but considering there is an issue and it's not coming up I don't know.
 
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I ran the extended hardware test, it said "No trouble found". I'm not sure if that is a good sign or not. Normally I would think yes, but considering there is an issue and it's not coming up I don't know.

If the problem is as simple as a loose/faulty cable, then I don't believe the AHT would reveal that. Of course that is good news, if that's what it is, but you'd still have to get in there to fix it.

Try rebooting into Safe Mode. If you have the same problem even in that, it's definitely hardware (including the cable) related.
 
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Ok, fingers crossed it's that. Thanks for your help, it is appreciated. I'm rebooting into safe mode now. I'll see what happens. It takes 8 attempts to even turn it on now. Flickers white then goes black straight away.
 
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Yeah, still persists in safe mode. Slight flickering. I'll get it looked at ASAP.
 
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Screen goes blank

I have a 3 year old 27" imac about 14 months after purchasing it the screen would go blank but the program would still run. The most painful episode was when i was chip leader in a $2000 dollar poker tournament when the lights went out then all i could hear was my chips being sucked away by the other players. I tried everything to fix the problem, Apple sent it to an authorised service centre guy who actually had it for 6 months! To be honest i didn't really want the thing by then so i didn't chase him. He could not replicate the problem. I just didnt want to throw away any more money at the thing so this is what i did. I bought a new monitor for $100 and put my $2000 Imac on the floor where it belongs. I connected the monitor d-sub to thunderbolt and selected the mirror option, perfect. Now i never have to worry about losing the picture. Coincidentally the imac has never cut out since presumably because the brightness is set to its lowest so heat was probably an issue but i really don't care now. Love the Imac but i really dont think i will go down that road again.
 
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chas_m

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To me these problems sound like a simple failing backlight, and should be easily repaired by a qualified tech.
 
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You would think so but i have read hundreds of cases on here in the past and on youtube relating to the 27" iMac backlight cutting out and there doesn't seem to be any one simple solution. Apple certainly know the fault exists on this model. I gave up in the end at least i have solved the problem even though it is may not be a conventional method
 

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