My screen has no backlight

I have a similar problem. My screen has no backlight but I do have video which I can just barely make out with a torch. I have tried using F14 and F15 to try and adjust the brightness but there is simply no brightness to adjust. But I can register an image on an external screen. I have searched the forums and found several articles which refer to soldering a jumper lead from the resistor below the third status indicator (near the right hand memory card slot) to pin 2 of the inverter cable. However, I cannot find this cleverly disguised inverter, nor can I find the cable attached to it. My iMac is a late 2007 model 1225, EMC 2134. Can anyone help with this vexatious problem?