iMac, broken led board?

[Thedog]

Hello,

At first this iMac occasionally turned black but the screen would then return a second later. Later it would go black and never go back on, I tried smc/pram reset to no avail. If I hook it up to a second monitor it works as expected and I can also see the screen on the iMac if I look from an angle above in a dark room. In other words it seems that the backlight of the LED is not working.

I googled and I found a lot of people saying that a broken led board would cause this. I have ordered a LED board but haven't received it yet but today I opened up the iMac to just look at things and prepare it for a LED board change. Im no expert in soldering, caps etc but can anyone see anything wrong with my current LED board? I am afraid that it's actually the monitor and not the led board but I really hope not...

I have an volt meter and there is some labeled pins on the actual board but I do not know how to do some basic testing on them.

 

[Bizybone]

I'll chime in and say that it is most likely the LED board.

I can't answer your other question.

 

[Thedog]

I'll chime in and say that it is most likely the LED board.

I can't answer your other question.

What do you base it on? Have you seen this error before and know it's led board?

 

[Bizybone]

What do you base it on? Have you seen this error before and know it's led board?

Back when I worked for an Apple Authorized Service Provider it was very common for these iMacs (21.5 and 27-inch) to come in to the shop with the same exact issue.

I don't recall ever having to replace the actual LED display, unless I was one of the lucky ones.

edit: But the fact you said you could see an image at the right angle tells me the display is good.

On the older iMacs (20 and 24-inch), the back light board used to fail a lot too.

 

[Thedog]

Great to know! Thanks for your input, makes me more confident the board is the right thing to replace. I had another iMac which would make buzzing sounds whenever the brightness was set high, that time it was the power supply. The iMacs seems to be a bit low quality in general I think.

 

[Bizybone]

No problem.

Also, IIRC, The display itself does not have a back light board since it's LED, that task has been handed off to the LED Board.

Shining a flash light into the display to look for an image or playing the the trying to brighten the display with the keyboard commands would be my way of confirming the LED board being bad.

Where the LED board plugs into on the Logicboard could also bad but it's highly unlikely in my experience.

 

[Moltuae]

Are your concerns that the board has no physically apparent signs of failure?

If that's the case, I wouldn't let that worry you. I'm no Apple expert, but as en electronics design engineer, I can tell you that it's very common to see components fail without any visible signs of damage.

 

[Thedog]

I've replaced the board but the issue persists did a PRAM and SMC reset after replacing it but still the same issue... suppose this computer goes to the trash? It's a pity

 

[Thedog]

Actually its now working! I started fiddling with this:
https://discussions.apple.com/thread/4041042

It did not work after I tried to press the cable to make suer they made contact. However, miraculously it started after a while and Im typing with this now... we see how it goes, I let the new board be in since there is no point in returning it due to shipping fees (I live in Europe)

 

[Markverhyden]

Great to hear.