iMac 27" Black Screen?

This is what i tried on my 2010 intel i5 imac

remove dust (one day good)

unplug and plug all the cables from the monitor including the small backlight cables in the corner (one day good)

set the sleep-mode to "never" (no effect)

set the brightness to 4 blocks (seems to occur less)

set the brightness to 6 blocks (seems to occur more)

PRAM reset (no effect)

SMC reset (longer problem-free intervals after reset)

set the brightness to 80 % yesterday (didn't occur since)

turn off the bluetooth an hour ago (didn't occur since)

i have a wired keyboard and mouse.

it occurred in cold and hot conditions.

it occurred several times while browsing and playing minecraft.

it didn't occur once in screensaver mode.

When it happens it happens several times in a short time.

it occurred once in mavericks the day before i upgraded to yosemite.

After the upgrade to yosemite it went a lot worse.

it occurred while running ubuntu from a USB stick.

I hope this helps, if everyone analyse the conditions in with it happens maybe we could one day find a real cause.

It drives me mad,

Thanks Manuarmata. That's interesting, the one thing I hadn't tried was setting the brightness slider. On opening the monitor panel it was set to about half way despite the monitor always looking as though it was on full brightness, so I set the slider to full brightness and for the first time today I'm able to use the primary monitor. This could of course be pure coincidence, but I'll post as an when anything different happens.

Cheers

I have a late 2009 iMac 27 inch.

If I raise the brightness above 1/3 it goes black. Hitting OPT, COM, Eject then any key will wake it up again.

Computer stays running, monitor goes black. I have an external monitor so I know the computer stays running.

I use a wired keyboard.

This happened before Yosemite, and with Yosemite. Now, the mac is back to pre-Yosemite.

I took it to the Apple service place and they replaced the video card. That did not solve it.

They said I need a new monitor, $800 (and here in Seoul, a new iMac 27 is $2500)

The darn monitor works but only below 1/3 brightness.

I can now confirm that the brightness keys (or slider in the display prefs) seem to be playing their part. After turning brightness up full I was able to keep the monitor on and got a full day's use without blackout. So the next time it repeatedly blacked out when trying to wake from sleep, I turned the monitor brightness down to about a quarter and it consistently stays on (although having the screen that dark is pretty useless.) As the brightness goes up a bar at a time, blackout hits at a point somewhere just before half way. Both these behaviours currently seem repeatable and reliable so it must mean something.

I do remember brightness set to zero used to fade the screen to black, but at some upgrade of the OS that behaviour changed to barely visible.

I also remember reading another thing related to the HD swap I got as part of Apple's replacement program. The article suggested that some SMC related connection may have been loosened during the hard disc replacement. I can't remember the link offhand but if anything comes of that I'll post.

Cheers

Savbox Your imac seems to play up exactly the same as mine!!!we have the same problem with the brightness,every so often on mine i can turn the brightness up to half and it stays on for days,one mark over half and it black screens.

As i type now i have it on Brightness 3,i have just increased brightness to 5 and it black screens,i now have it at 4 and it has stayed on.

This is a joke and now even more people are having the same problem,waste of time getting in touch with Apple.

That sounds very familiar Steve! I may have just stumbled on to something else. Are you turning the brightness up via your keyboard keys or via the system prefs>display>brightness slider?

I ask because the first time I turned it up full (a few posts back, Oct 24, 2014 3:34 PM ) I used the slider in system prefs. all the other times since I've been using the keyboard keys, but just now I turned it to full via the sys prefs slider and it has stayed on at full brightness. From now on when it blacks out I'll use the display prefs slider to see if this is a repeatable pattern as that might suggest a problem with the way the iMac and brightness keys communicate.

Cheers

I doubt it is a communication problem. I had blackouts in linux and other people talk about blackouts in windows. Personally i think it is a semiconductor problem. It is way to unpredictable to blame it on software or firmware. if just someone with very frequent blackouts could monitor the input and output voltages of the backlight controller we could get much wiser.

When we monitor the voltages during a blackout and one of the voltages drops we can replace it with a current from another source witch should be possible for someone with some electronic skills.

If all the voltages stay it is probably a transistor in the led board witch convert the 24 v current to a lower voltage but i doubt that as the left and right side are controlled separatly.

If a semiconductor is likely to deteriorate or develop faults over time then perhaps you're right. In my 20 year experience with macs so far it would be a first and this particular iMac has indeed been working perfectly for 4 years. Only in the last month or so has it started blacking out, which is why I was wondering if some recent upgrade glitch has caused it. For me it's the obvious first step to try anyway. The HD was replaced about a year ago (even though the old one showed no signs of failing) and the machine also continued to work perfectly after that so I think the dislodged wiring theory doesn't fit either.

My screen did black out again and so before putting it to sleep I used the monitor keys to turn the brightness setting down (obviously guessed how long to hold the key down as I couldn't see the screen dimming, it was already black.) Using my second monitor, I then woke the machine up, opened prefs>displays>gather windows then turned the iMac screen brightness slider back up to full. I put it to sleep again, woke it up and for a third time using this method the screen came back at full brightness and is still currently working. Guess I'll keep doing it until the method fails!

Cheers

Well,

I took my late 2009 iMac 27 to the Apple place and they tried power board, no. Then they said "monitor for $500" and I said no.

Then, I took it to a tech repair guy, he changed power board $250, and that did not fix it. He then said "monitor for $480". I said no.

He gave me a 30 day-guarantee, so I got $200 back. He earned his money.

I think the bottom line is, the Mac's are made in big, indivisible units. The cause may be a loose wire or $5 part within a much bigger part, but there is no way to get to it. They are not make to be repairable. There are no small parts, and the big parts are designed to be replaced, not repaired. End of story.

I did have a gut feeling it was related to temperature but this morning it happened as soon as I switched the iMac on so possibly not. I still get the blackouts occasionally but the situation has stabilised and become more predictable since I started my routine; when a blackout occurs, turn the brightness down using the keyboard(guess how long to hold it down for) > send the machine to sleep then wake it back up; the screen always comes back at low brightness > don't turn the brightness up via keyboard but open the display prefs and up the slider to full. This always keeps the monitor on at full brightness for a few days. When it blacks out I do the same thing and again, stable for days.

Interestingly a couple of days ago I thought since it was still happening, I may as well go back to using the bluetooth keyboard. The persistent blackouts came back almost immediately. I tried Manuarmarta's suggestion of 80% but in that situation it didn't help. When I reverted to the usb keyboard the relative predictability came back. Perhaps a coincidence and I can't think why the bluetooth keyboard would contribute, because I also have a bluetooth mouse and Wacom Intuos Pro (I have tried switching all bluetooth off but that didn't stop blackouts.)

One thing is for sure, it seems pointless taking the iMac to get fixed because as this post also shows, people are consistently paying out huge amounts of money without joy. Only nihaocaro's solution seems to have worked so far. It would be interesting to hear if this same solution resolved anyone else's blackouts.

Cheers

Well, this is strange but good.

Instead of adjusting the brightness with the keyboard, I went into the display systems preferences and un-clicked everything un-clickable and clicked them back. Then, still in the systems preferences, I adjusted the brightness to full blast.

The darn thing works. For now.

Well, a week ago, in the "Systems Preferences" under "Energy Saver" I unchecked the "Put hard disks to sleep with possible" and, the other two boxes under that, and my monitor is working perfectly.

I suggest unchecking all boxes on the Screen Saver and see what happens. It worked superbly for me.

Mine worked well for a week with the monitor at 80 % then it went black twice, now with the monitor an 100 % it works now for 10 days without issue. Fingers crossed but i think about changing the led inverter board myself eventually. it wil cost me 200 €. It contains capacitors and i begin to suspect them. @ cyrano, what parts are actually changed in yours?

It was the blah blah board. About 5 x 8 inches.

When that failed, they wanted to change the monitor panel (I hope I am using the right terms)

Like many car repair places, I believe they use the slash-and-burn approach. They just change parts, which I understand, because there is no profit if they go digging around for a long time.

I was quoted 2 prices, $250 for the board, and $480 for the panel. The odd thing is that changing one little setting on the energy saver made it work for a week.

Some setting or connection must be very skittish. And I understand it is not cost effective for them to find the loose wire.

I had this problem with 3 different OS, from 10.9.3 to Yosemite. I'm in Korea, which has hot summers and cold winters. It is cool now, and the problem still occurs, so it is not temperature related.

Think I have found my problem, fixing it maybe a different story. It looks like the plug between the display and the motherboard has failed as there is nothing holding motherboard side of this plug down or to the motherboard. As I put the screen in each time I moved the screen it blacked out and by moving the RHS cable the screen came back on.