After following Apples LED diagnostic test and confirming the diagnosis at the "genius" (not) bar I purchased a new logic board for my iMac G5.
Following iFixits guide the logic board replacement went smoothly and without incident. Congratulations on a well produced and thorough guide. My only complaint is that the red circles showing screw placement are difficult to see if you happen to have red/green color blindness.
After replacing the logic board with a new one and plugging in the power cord-voila! nothing- nada and more nothing. Same LED diagnosis as before! I assumed I had purchased a bad logic board. When I contacted the seller (Niktec) they assured me the board was good and that I probably had a power supply problem-advice totally contrary to the Apple support site and the Geniuses -did I say not, enough? Fortunately I happened to have my girlfriends iMac, which was working, and swapped out the power supply (which I had learned to do with iFixit). Bingo-it's alive, it's alive!!! Moral of the story- tread warily in the Apple cosmos!!