Control black screen on 2009 iMac

[Mike Musial]

My Machine: A1312, EMC 2374, iMac 11,1; late 2009 27 inch iMac

After struggling with very regular bouts of screen blackout to the point where the computer is unusable, I found, with the help of this forum, a working solution that eliminated the problem. It has caused another problem.

By dimming the brightness control (running right now at three bars), those random blackouts are gone, and the computer is 100% functional. However, the screen is dark to the point of eye strain. Increasing the brightness control, even to 50%, and the blackouts immediately start happening again (like within 3 seconds).

I saw a post in this forum that indicated that the LED strip lights within the LCD panel can be failing, and could be the cause of this unusual behavior. Can someone confirm this? Thank you.

 

[Nguyen Duc Hieu]

My Machine: A1312, EMC 2374, iMac 11,1; late 2009 27 inch iMac

After struggling with very regular bouts of screen blackout to the point where the computer is unusable, I found, with the help of this forum, a working solution that eliminated the problem. It has caused another problem.

By dimming the brightness control (running right now at three bars), those random blackouts are gone, and the computer is 100% functional. However, the screen is dark to the point of eye strain. Increasing the brightness control, even to 50%, and the blackouts immediately start happening again (like within 3 seconds).

I saw a post in this forum that indicated that the LED strip lights within the LCD panel can be failing, and could be the cause of this unusual behavior. Can someone confirm this? Thank you.

What else can fail in this case?

 

[DeltaMac]

There is the LED backlight board, near the power supply. You could try replacing that. If no help, then the LCD panel is probably to blame.

 

[Mike Musial]

Day 2

More searching of the internet, and two ideas -----

1) cover camera when you increase the brightness. This worked.
2) put brightness control at its brightest. That also worked.

Computer worked all day. It would go to sleep after the display was on for 30 or 45 minutes (it was idling, that is I was not using it at all), but it was not the blackout screen. It was a screen that was dark grey, and a screen that would immediately come back with the pushing of a key on the keyboard.

Also saw a post that indicated you should open terminal and type in 'caffeinate'. That prevents the computer from sleeping. That also worked. It really did!

So, it doesn't seem the LED strip lights are the problem.

BTW, I am strictly an amateur, but I only paid about $140 for the computer. I am just having fun

 

[Mike Musial]

There is the LED backlight board, near the power supply. You could try replacing that. If no help, then the LCD panel is probably to blame.

I had already tried that without effect. Please see my Day 2 comment. Things are better.

 

[Nguyen Duc Hieu]

Day 2

More searching of the internet, and two ideas -----

1) cover camera when you increase the brightness. This worked.
2) put brightness control at its brightest. That also worked.

Computer worked all day. It would go to sleep after the display was on for 30 or 45 minutes (it was idling, that is I was not using it at all), but it was not the blackout screen. It was a screen that was dark grey, and a screen that would immediately come back with the pushing of a key on the keyboard.

Also saw a post that indicated you should open terminal and type in 'caffeinate'. That prevents the computer from sleeping. That also worked. It really did!

So, it doesn't seem the LED strip lights are the problem.

BTW, I am strictly an amateur, but I only paid about $140 for the computer. I am just having fun

This means there is a Light Sensor in your iMac?
I'm just curious.

Change your Mac display’s brightness

Change your display’s brightness manually or automatically.

support.apple.com

 

[Mike Musial]

This means there is a Light Sensor in your iMac?
I'm just curious.

Change your Mac display’s brightness

Change your display’s brightness manually or automatically.

support.apple.com

Hi

The post I read advised that I should cover the light sensor at the top of the display. The only thing I could find at the top of the display was the camera. I don't even know if that has a sensor.

What I know about computers you could fit in a hat, but I am having fun learning.

 

[Mike Musial]

Day 3

Regression, but probably because of things I did.

I have two 27 inch iMacs, this one which has given me so much trouble, and a better one that I intend to sell because, well, it is better. I switched SSDs, putting a 1TBGB SSD in this computer, and a 200GB in the computer I am selling. I reversed the locations of SSDs

Anyway, the blackout screen is back on this computer. Right now it is working. I have enabled 'never go to sleep' and unenabled (is that a word?) 'put hard disks to sleep when possible'.

BTW, this computer is an 11,1 and the one I am selling is a 12,2

 

[wilberforce]

Hi

The post I read advised that I should cover the light sensor at the top of the display. The only thing I could find at the top of the display was the camera. I don't even know if that has a sensor.

What I know about computers you could fit in a hat, but I am having fun learning.

The light sensor is 1/4" to the left of the camera. Look at it very closely with a bright flashlight

Edit: actually I am not sure for the 2009 iMac. But that is where it is for most iMacs

 

[Mike Musial]

Hi, and thanks for the info.

After removing the display glass, I think I found it.

 

[wilberforce]

Not sure if you have this technician guide:

https://tim.id.au/laptops/apple/imac/imac_27_late09.pdf

 

[Mike Musial]

Thanks again, very helpful.

 

[Mike Musial]

Day 4

No explaining this.

Computer 100% functional. It was so bad the other day, and now, no problem.

The one thing I did do was to increase speed of the CPU fan, as that fan is, I think, the fan closest to the PSU. The PSU was running hot, and maybe the machine was shutting down because of the high heat associated with the PSU. Who knows?

 

[eyup]

Cheers!
This thread sorted the same problem - black screen after a short while after booting a 27inch Late 2009 iMac.
Screen would come back on after putting it to sleep (cntrl + shift + eject).
Running fine now if I put it at 100% brightness!
Also works OK when brightness is less than 50%. Very odd indeed.
I'd previously replaced the thermal paste on the GPU and CPU to no avail.