No video on lcd or external monitor

Hi, I have a Imac 20" A1224 model that will chime, boot off the hard drive and DVD drive but will not show any picture. I have reseted the lcd cables and reseated the gpu without change. The leds show the following when powered on 1-on 2-on 3-on 4-off.

I have done all the normal troubleshooting like reset smc, pram, ect.

I suspect the gpu will need to be replaced and I was wondering if anyone else has had a success story with the symptoms I've described.