iMac 8,1 (2008 alu 24") blank screen

Hey Guys,

I've got a 2008 aluminimum 24" imac. 3.06GHz, 4GB, 250GB. The screen started to just turn off around 2 weeks ago. Sometimes the machine would power on and work for around 1-2 hours, but sometimes only around 15 minutes.

The screen just goes black. No funny flickering, no odd pixels etc. Just off.

The superdrive is still reading etc, if I put in a disk it spins and reads, I can also hear the hard drive reading etc.

I opened the imac and checked the graphics card. Its the 512MB Nvidia 880GS.

I sent the graphics card to a company to test it and it worked directly in one of their machines for an entire day.

I've replaced the ram and the lcd screen too.

When I power up the machine I check the little diagnostic leds and it shows

LED 1 - ON
LED 2 - ON
LED 3 - ON
LED 4 - OFF

but the screen is just black.

Any ideas - I'm thinking it may be the logicboard but surely the dvd drive and hard drive wouldnt power on?

 

Hey,

I've not checked the invertor, but I have tried two complete lcd screens - the LCD's have the inverters installed so I'm guessing they are fine...

If the logicboard / mainboard has failed would the dvd drive etc still power on?

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I have noticed though none of the fans are coming on when I turn on the machine....