Tough iMac Black Screen Issue

[dswallace]

My screen goes black at random times for random reasons.

• First, medium brightness levels went.
  • Solution: Use lowest or highest brightness.
• Then high brightness starting going to black screen.
  • Solution: Force sleep (cmd+opt+eject) and then wake after 2 seconds.
• That held me over for a while but then the screen started going black a few seconds after waking again. I progressively found solutions which fixed the issue for a week or even a month:
  • Solution: Dump chrome cache when it hit 600 mb. Then 300 mb
  • Solution: Dump all chrome cookies.
  • Solution: Reset the PRAM or SMC
    • (each of those only worked once)
  • (Caffeinate never helped)
• Currently it only works at lowest brightness or randomly at highest brightness. The force sleep sleep/wake trick still works, it just doesn't last a full brightness. Today anyway. A week ago it had been fine for a month. Seems to happen on Fridays. Maybe we're emotionally bonded.

It's 2010 fully packed iMac running 10.13.6. Was on a stable version of Yosemite for years, just updated last week hoping for a fix but no luck. Better performance though. Motherboard and HD replaced 5 years ago. This started around year ago, about 4 years after the HD and motherboard replacement. It had a black screen issue when I bought it, sometimes going black on startup or refusing to wake from sleep. A good 2-second power button push or restart always did the trick though.

Fan control says the temp is low, and it can get really hot on the top left without a problem. I read there was a vulnerability in these machines where cookies (from China, planted on a variety of websites) could force the black screen. This was how I discovered the cookie trick. I took the screen off and cleaned it out (it was pretty good though) and found 10-15 pin cable was loose. Everything else looked find, but maybe I should bake the GPU? Anyone do that successfully? I used to play a lot of games on it, but not for a few years. I'm old and my soul is dead now.

I just need it to last until the new MacBook pros release x-D

 

[DeltaMac]

When the screen goes black:
Shine a bright light into the screen, moving the light around. Do you see any screen elements (top menu bar, icons, windows open on the screen) even though they may be very dim?
If you see those icons, etc. then you likely will need to replace the LED backlight board (GPU is probably good, just the backlight stops working)

 

[dswallace]

Thanks! Something like this then?
Mac Backlight board

 

[DeltaMac]

Yes, something like that...
Make sure you get the proper part for your model iMac. You did say that you hve a 2010 iMac, 27-inch.
That part you linked is for a 2011 27-inch.
Here's a link at the same site for the correct part for a 2010 27-inch - LED backlight board

 

[dswallace]

Replaced the part, LED backlight board.

No change. Any other thoughts or suggestions?

 

[DeltaMac]

Next would be the power supply, I suppose.
Have you tried an external display yet?
Then, replace the LCD panel.
You COULD try baking the GPU, but I doubt that as a permanent fix. Won't hurt anything to try that, however.

It's likely simpler to look for a complete iMac for sale on eBay, or similar.

 

[Fishrrman]

OP wrote:
"Replaced the part, LED backlight board.
No change. Any other thoughts or suggestions?"

Yup.
It's 9 years old.
Don't waste any more money on it.
Start looking for something new, or at least... "newER"...

 

[mikehalloran]

When the motherboard and drive were replaced, did someone install another HDD and keep the same battery?

If the answer is yes, the innards are cooked.

It's 9 years old.
Don't waste any more money on it.
Start looking for something new, or at least... "newER"...

Yep.