Backlight off after "pop" noise

Hello everyone,

I need help with this one as I am dreading the cause to be the graphics card again….

A week ago while using my iMac it made a “pop” noise - much like a capacitor breaking. The screen went black. Using a torch I could see that the LCD was indeed working, just the backlight of the LCD turned off.

I went through the Technicians diagnostic steps.

I’ve replaced the Backlight Board, no change.

I’ve replaced the complete LCD panel, no change. This also changes all cables in the process.

I have a feeling that the main power board might be at fault here, but the diagnostic steps end here. Can anyone tell me what voltage I would need to see and when at the Backlight Board power supply side? There are 6 pins, I understand that pin 3 should be live to enable the backlight?!

1. Do I need the LCD connected to be able to take a valid measurement there?
2. What kind of voltage do I expect?
3. Are there schematics available to give me an indication?

I’ve replaced the graphics card once already. I hope it is not due to it again (backlight enabling voltage etc…).

Any input is mutely appreciated.

Many thanks,

Rob