24" iMac Screen Dim Humming

I have recently noticed that when my iMac's screen auto dims, a faint humming noise comes from within the iMac. Is this normal?

I have heard of this happening but I do not know how normal it actually it because mine does not do it. I would do a little forum searching because I know the topic has been discussed here before.
George

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IMac screen dims itself automatically; all attempted fixes fail; how can normal brightness be restored?

Machine and OS:
2007 white plastic iMac with 20" screen and 2 GHz Intel Core Duo, running OSX 10.6.8.
The problem:
The screen dims itself for no known reason. It is especially noticeable when waking from sleep: for the first second or two after waking up, the screen is at normal brightness -- but then after a second the computer seems to "remember" some setting or command, and the screen unquestionably dims itself to be about 20% or 25% darker.
Because the screen for a brief moment after waking is at full brightness, that proves to me that there is nothing physically "broken" about the display that prevents it from illuminating fully; it could be at full brightness if it "wanted to," but some kind of software or firmware glitch is telling it to be dimmer.
The fixes I have attempted so far -- ALL of which have FAILED (so please don't recommend them again):
- Reset the NVRAM or PRAM by holding down Command-option-P-R upon startup. For some reason this technique doesn't cause the second chime, so it doesn't appear to be zapping the NVRAM or PRAM or whatever, and consequently has no effect on the dimness, which persists unchanged after restarting.
- Reset the NVRAM using the terminal command ' sudo nvram boot-args=”-p -r” ', as recommended on this page: https://discussions.apple.com/thread/2172681?start=0&tstart=0. I can't tell if this really did reset the NVRAM (it doesn't cause a second chime upon restart), so I'll just have to assume that it "worked" -- but except for one instance, it had no effect on the screen dimness. (That one instance went like this: after issuing the Terminal command and restarting, the screen did go back to full brightness -- but only until the first sleep. After waking from that sleep, the screen once again dimmed itself as before. And no, I have not been able to repeat this momentary "success"; on all subsequent attempts following the exact same steps, no brightness has ever returned at all since.)
- Reset the System Management Controller (SMC) as recommended on this page: http://support.apple.com/kb/HT3964 . Basically this just entailed shutting down the computer waiting a few seconds, then unplugging it, waiting a few more seconds, then plugging it back in, then waiting a few more seconds, and then finally starting it up again. Result? No change: screen still dims itself.
- Pressed the "brighter" and "dimmer" keys on the keyboard; those do make the brightness go up and down, but the top brightness setting is much dimmer than it should be (and used to be). All the way to brightest setting = still noticeably dimmer than normal.
- Used the "brightness" slider in the System Preferences > Displays > Display window. That also does indeed adjust the brightness up and down, but as with the keyboard brightness keys, the highest setting is still too dim.
- Readjusted the "Calibration" in the System Preferences > Displays, which had no noticeable effect; even when going into Expert mode and adjusting every little aspect of the screen display's default settings. Those all seem to be about color balance anyway, not about brightness. I now have three different new calibration settings, and clicking back and forth between them and the default setting makes no real significant difference. Whatever setting I choose, it is still dimmer than it should be, even though in all my attempts at calibration I tried to make it brighter.
- Tried going to System Preferences > Universal Access > Seeing and adjusting the "Enhance Contrast" slider and trying out "Black on White" vs. "use Greyscale"; none of that helped, and did not seem to be relevant to the problem.
- Tried going to System Preferences > Energy Saver, and clicking the "Automatically reduce the brightness of the display before display sleep" check box on (and then closing the preference pane) and then off again (following the advice at http://support.apple.com/kb/TS2309?viewlocale=en_US) -- but it had absolutely no effect whatsoever on the brightness level.
Final note: The keyboard and mouse are both Apple products and work perfectly, and the machine has no other performance issues. Just the dimming, which started a few weeks ago inexplicably and without warning.
I can't imagine what is causing this problem, and I've absolutely run out of ideas about how to fix it. One thought I had was that maybe the screen is dimming itself due to detected ambient illumination, but I'm not sure 2007 iMacs even have that feature, and also the screen remains dim whether the room is dark or bright. Maybe there is an ambient light detector somewhere that is malfunctioning?
Help! How can I solve this? The screen is not so dim as to be unusable, but it's annoying enough that I'll have to get a replacement machine if this is not fixed eventually.

Does an external display also act in a similar manner as the internal one?
Some earlier Intel-based iMacs had graphic processor card issues; not sure what
the symptoms of the majority of them were, but some had odd patterns, others
went black, and some would range from OK to totally unusable. Among others.
So there is a chance the graphic processor may be going out; or just the circuitry
that controls the backlight. An inverter may be weak or other circuit to the display
could be wearing out.
http://www.apple.com/retail/geniusbar/
If you have access to an Apple Store with Genius bar, they can perform some kinds
of diagnostic tests there even though the computer is out-of-warranty; that may be
of help to narrow down the cause of the symptoms you've noticed. They may not be
able to repair it, however, at an Apple Store; as it is rather old by today's standard.
An Apple Authorized Service Provider could do repairs and testing on older models
the Apple Store's Genius and other may not be set up to handle due to vintage.
Find an Apple Authorized Service Provider
Visit an Apple Retail Store
There is a country locator page to help find either of the above in regions outside
of the US & Canada, not sure how the above links would work; and it appears my
bookmarks to the country locator page may not be accessible now to post here.
You may be able to get an idea about what kinds of parts support the display
function by name by looking into an iFixit.com repair guide for your iMac series.
Hopefully the parts supporting the display are the reason it is dimming down, as
a graphic processor failure likely would exhibit other behaviors than just dimming.
PS: I see you've added content to your thread after I'd started working on this
& the answer likely is a hardware repair; professional testing is worth the time
and you seem to have at least one other thread on the same topic....
Good luck & happy computing!
edited 2x

IMac Screen Dimming

About a week ago my screen started to randomly dim and then get bright again. The auto brightness is turned off. Its very random when it does it, Im worried the screen is starting to going bad or something. I purchansed the computer new at the end of 2011. Its a 27" iMac 2.7 GHz Intel Core i5, Graphics AMD Radeon HD 6770M 512 MB. Is anyone else having this issue? All of my software is up to date.

First, some commentary:
http://news.cnet.com/8301-13579_3-57609897-37/apple-sued-over-alleged-imac-scree n-dimming-issues/
https://discussions.apple.com/message/22938701#22938701
This issue results usually from two things: the brightness settings, or the graphics card. It seems you've already accounted for the brightness settings, so you might want to investigate the latter.

Imac screen dims and two browser windows flicker.

Not sure how to explain this, but when I have two browser windows open, at random, they start to flicker and the whole screen gets dim.
What can I do?
Thanks

I just noticed that when it happens, the mouse pointer stays with the hand icon.
Then when I move it to a window, that window goes dim.
Can someone explain this?
Thanks

IMac screen dims immediately after logon

Have a weird problem with a 1-2 year old iMac. It's running Leopard, and as soon as anyone logs into it, the screen immediately jumps to it's lowest setting. This forces every user to open apple-->system preferences-->display to move the brightness setting back up to full. It doesn't matter who logs in, with their network account. How can we remove this behavior?

See if a PRAM reset helps.

IMac screen dimming problem

Can someone please tell how to fix this? I believe it may be a hardware issue, but when I reload the iMac, it goes away. When I put my HDD image back, the problem starts up again.
Note: this is networked iMac (it is bound to a AD domain). This only happens after the iMac has been sitting idle for enough time to log out.
Here a video of the problem:
http://www.youtube.com/watch?v=gpNCKdP5wo0
Thanks!!

Hello,
The 2012 macs (and later apparently) not waking normally from sleep after hours being in sleep. (noted here ...
http://www.xlr8yourmac.com/archives/feb13/022813.html#2012macswontwake
"Why 2012 iMac/2012 Mac Mini won't Wake After Hours of Sleep (Hibernates/Powers Off)")
The sleepimage file still reappears even if never slept. Delete it (hibernate off, etc) - within minutes its back.
Anote on that here - http://www.xlr8yourmac.com/feedback/Chameleon_SSD_Optimizer.html
About iMac sleep, but...
http://forums.macrumors.com/showthread.php?t=1529750
https://discussions.apple.com/message/22336226#22336226
Daniel Leary 2008
Re: Mac Mini wake up issues
Okay this workd for me, I typed into Terminal:
     sudo pmset autopoweroff 0
     sudo pmset standby 0
then verified that the changes were made with
     sudo pmset -g
and so far so good!

IMac screen going dim . . .

Lately my older imac screen has been somewhat dim when waking from sleep.... only happens sometimes, seems to be normally bright at the bottom, growing dimmer the further toward the top you look .... if I restart, everything is fine again.
Hardware problem? Seems unlikely since it seems unrelated to how long the computer has been on, it's immediately fine on restart. Any ideas appreciated . . .

Some problem with my iMac. Took it back to the Apple Reseller, they 'repaired' it after 3 weeks. Got it back, still the same problem. Called them and they said is was a normal buzz which the inverter card(?) makes, like the fan and the HD.

IMac 400 dim and jumpy screen

Sorry if this has been covered already -- I could not readily find a thread about this. Like some here, my DV 400mhz iMac screen is dim, and none of the things I've read here will brighten it up. I have to go into calibration and make some odd changes to get it bright enough to read certain web pages, for example.
But I learned to live with that. Now the screen is also "jumping," or wiggling from time to time -- just enough movement to be perceptible, and annoying. I fear the whole thing will be going out before I take steps to fix it, or replace it.
Can you hook up an external monitor to an old 400 mhz iMac? Any other ideas about the jumpiness and dimness? Thanks.

Sounds like the high voltage is going out. The jumping would be the HV filter caps going south.
A standard VGA monitor can be attached under the back behind the oval perforated grill.
Richard

Imac screen will dim after leopard install

Since installing leopard on my imac the screen will dim a small amount after awhile and then when I star to use the mouse it will brighten up again. Is this normal with leopard?
My Mac pro dors not do this.
Thank you
Dcik

Ever since I installed Leopard on my iMac G5, periodically the screen will dim. This seems to be random, and not related to any specific program I might be running. The screen dims to the pre-sleep level, and doesn't brighten in response to anything I do other than sleep the computer and wake it again--no keystrokes or mouse clicks have any effect. I've tried everything in the Energy Saver prefs, and nothing seems to make any difference. Fortunately it doesn't happen all the time, or it'd be a real nuisance, but for that reason it would also be difficult to reproduce the effect for a repair person, in the event that it's a hardware problem. Has anyone else encountered this?

My iMac screen goes bright and dim randomly, any idea why?

my iMac screen goes bright and dim randomly, any idea why?

Sounds like a power issue.
Try Resetting the System Management Controller (SMC)

Any news on imac G5 20" screen dimming?

I have been living with the top half of my screen dimming intermittently for the past 4 months or so. The bottom half stays bright. I have to sleep the computer to bring it back and it's a pain. I brought it to the Apple store a couple months ago (my machine falls into the recall serial #s) and the genius said the capacitors are fine and that it was due to bad memory. I pulled my aftermarket memory - and it still does it. I saw a lot of people asking about this months ago but never saw any definitive answer. Thanks - 1st post
imac G5 20" Mac OS X (10.4.5)
imac G5 20" Mac OS X (10.4.5)

gdan7:
I had this problem when Apple replaced my screen for the "white banding" on the lower half of the screen. Take a look at these instructions for replacing the inverter. If your comfortable with working around the internals of the machine this may help.
http://manuals.info.apple.com/en/imacG5_20inchInverter.pdf
When you open the document it will show you the internals of the G5. If you go to page 11 it shows a little connector inside a little grey box. If that connector is not seated properly you'll get the half-screen dimming. All I did was reseat the connector and made sure all the twists were out of the cable to make sure there was no stress on the connector. It worked fine after that.
Good luck.
Dan Reilly
Sarasota, FL

Dimming iMac screen

I've been using powerbooks for the last few years, and the dimmer keys will gradually dim the screen from bright, to dim, to almost dark & then compleely dark.
On the iMac, it dims the screen, but not to the same degree as the powerbooks. I'd like to make my screen darker than seems possible.
Is this a normal function of the iMacs?
Thanks

The iMac screen is bright - especially in the normal room lighting conditons (as opposed to office lighting). For normal viewing gamma 2.2 and white point 6500 are best (native gamma and white point can also be used as they are close to these values) Gamma 1.8 looks pretty bad on these machines.
If that is still to bright you can make a dark profile in the Display pref pane's color calibration area with the expert settings (pull all the sliders down) - but that really will only increase the contrast - for the most part the whites will stay just as bright.

IMac 24" Aluminum screen dims like notebook

So this is kinda weird. For some reason if I do not do anything for a minute (move mouse, touch keyboard) the screen dims like on the notebooks when they try to save power. Something tells me this isn't right... Anyone have any ideas or experiencing the something?

Google: [10.4.12 ?|http://www.google.com/custom?q=10.4.12+?&sa=Search&client=pub-626330033301395 7&forid=1&ie=ISO-8859-1&oe=ISO-8859-1&cof=GALT:%23008000;GL:1;DIV:%23336699;VLC: 663399;AH:center;BGC:FFFFFF;LBGC:336699;ALC:0000FF;LC:0000FF;T:000000;GFNT:0000F F;GIMP:0000FF;FORID:1;&hl=en]

The screen dim on 24 inchs imac

The screen dim before sleep on an Intel-based Mac's built-in display, even if the Energy Saver setting "Automatically reduce the brightness of the display before display sleep" is disabled. This setting may no longer be in effect after restarting the computer.
any body has a fix for this.
see the bug description at.
http://docs.info.apple.com/article.html?artnum=304092

Yes, I do, I am hoping for a permanent fix from Apple, but in the mean time I have a script which will run each time you reboot to disable the screen dim.
I have posted this as a separate thread.

How to keep iMac screen black while keeping secondary monitor running for visual experiments in Matlab

Hi,
I'm trying to run a visual experiment using PsychToolbox in Matlab.
I've attached a secondary monitor to my iMac for this purpose and I'm having difficulties trying to
'black out' the iMac screen.
I need the secondary monitor to run at a refresh rate of 120Hz and at linearised luminance (did this for my secondary monitor),
so I can't really use my iMac screen. However, i need my iMac screen to be darken out because I'm doing a vision experiment.
I tried dimming my iMac screen but it doesn't go completely dark. I tried Ctrl+Shift+Eject (or was it Command) but it will darken both
monitors. I also tried mirroring, but it doesn't seem to work too.
I'm really stuck and any ideas will be greatly appreciated!
shui
NB:I'm using OS X Version 10.8.3.

I do not know the details of your experiment, but creating a black monitor is not difficult. For example a completely black page, e.g. in Power Point, set to fill the screen?
The advantage of doing this with PP is that you can move in to or out of the black page with just the space bar. You can set up your monitors so PP is displayed on just one monitor.

24" iMac Screen Dim Humming

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