Replaced Backlight LED Board - Not It

[StockDC2]

Hi, so I have an issue with my iMac where the backlight is not working. The computer works great when hooked up to an external. I've replaced the LED board to no availability. Does anyone know how to check the current from the power supply to the LED board? Is there a possibility that the LED lights on the LCD panel itself are dead? Thanks.

 

[2macman]

backlit

I have a late 2009 27 iMac and there is a problem with the monitor. MANY people report a problem. The computer works but the monitor goes black. Often the monitor goes black if the brightness goes about one half or one third. That happened with mine and not it is black all the time. So I use an external LG monitor.

The strangest thing. The 27 monitor does now work with itself, the 27 computer. But, the computer will drive an external monitor.
AND, the 27 works as an external monitor to my iMac 24.

So, the 27 monitor works, but only as an external monitor to another computer. And the computer works to drive another monitor.
What could that be?