iMac help please!

Dan86

Hi folks, can anyone help with an iMac problem please? 

Mid 2010 27" , keeps randomly going to a black screen. If you click the power button a couple of times it comes back on.
If the brightness on the screen is turned down to 1 or 2 bars, it runs without a problem whatsoever. Then with brightness back on it will go to black screen again within the hour.

When the screen is black, a torch shone into the display shows the system is all still running, image is there. Videos etc keep playing.

Resets have all been done. Then fresh sierra install, then backlight inverter changed, ran for 3 hours then when black again.

Any help would be much appreciated, thanks!

steveb

http://www.pro-tools-expert.com/home-page/2017/1/27/a-sad-story-with-a-happy-ending


Take a look at this, apparently thre was a graphics card problem on the macbook pros of that time. Maybe it affected the imac too. Looks like apple might repair free of charge!!! 

Dan86

Already had a chap from Apple check that. Cheers anyway though!

TonyR

A bit of a long shot, but it's not the "Display Sleep" kicking in is it?

Try looking in System Preferences -> Energy Saver and see what the "Display Sleep" time is set to.

ICBM

Sounds like something heat-related in the backlight supply if running it at low brightness stops it happening. If the inverter has been changed it just must be somewhere else.

bingefeller

USB or Bluetooth keyboard?

Flink_Poyd

Try disconnecting the keyboard and leave it running. If the screen doesn't go black obviously a problem with the keyboard communicating with the mac. 
 these sort of issues are a process of elimination 

Dan86

Tried USB razer keyboard and USB Apple keyboard , same problem with both. 

ICBM

It has to be just something to do with the backlight or its power supply if the computer is still running normally otherwise and it's related to the backlight brightness. It could be as simple as a cracked solder joint somewhere - the problem will be finding it. A lot of my repair work on amps is exactly this sort of thing.

Danny1969

My gut feeling is the LCD panel ... or rather the backlight in the LCD panel .... more specifically the connection to the panel which is a surface mount connector who's joints go bad and sometimes come away completely

Peel back the tape and look at the connection on the bottom left of the panel ...... don't work on this machine plugged in as the SMPS is un- insulated at mains potential just behind the LCD panel 

Dan86

Thanks for the info guys. Trying LCD temp sensor when it arrives . If it's not that I'll try another LCD unit

Wazmeister

TonyR said:

A bit of a long shot, but it's not the "Display Sleep" kicking in is it?

Try looking in System Preferences -> Energy Saver and see what the "Display Sleep" time is set to.

Seriously, I had this with mine. Reset the settings, and get rid or have the lowest energy saver options.

Mark_R

Have you cleaned out the fans and vent ports with a little brush/hoover on the base unit?  The screen takes its power from the on board system, so the brighter the screen, the more power through the board = more heat.  

Danny1969

Wazmeister said:

TonyR said:

A bit of a long shot, but it's not the "Display Sleep" kicking in is it?

Try looking in System Preferences -> Energy Saver and see what the "Display Sleep" time is set to.

Seriously, I had this with mine. Reset the settings, and get rid or have the lowest energy saver options.

I think he said he can see the video, so I don't think it's a sleep issue as sleep turns off the video and BL