Imac G5 Screen Not Working

[lc25]

So i have been asked to sell a Imac G5 as the screen doesn't come on at all just stays black but the hard drive does spin up, for a friend on eBay me being inquisitive i opened it up and checked the 4 little LED's to find that the 3rd one doesn't light up meaning that the logic board needs to be replaced ? (correct me here if i am wrong). My question is this if i was to get the vga adapter to mirror the screen onto a external display would that work or not ? . Failing that its the eBay i feel unless i can get a logic board stupidly cheap ? Any other idea's ?