IMac G5 (iSight) Black Screen and Won't Start...HELP!

Question

Hi,
I have an iMac G5 (iSight) PPC, 2005, model 1145.  All was running well until a couple of weeks ago (see post/thread https://discussions.apple.com/message/16191999#16191999), when I had an issue with a grey screen, no start, and spinning wheel.  Through a series of replies, it was determined that I probably had a corrupt file in the OS (10.5.8).  I did an Archive and Install of the OS and all was running very smoothly....until....NOW!!!!!!!
At this point, I cannot start up at all.  When I turn on the computer, I get a 'light', but in a few moments, the fan gets loud, stays loud, and the screen is just black.
I tried to start up from my Leopard Disk, hoping I could run the utility....but that didn't work....AND NOW I've the install disk stuck in the drive!!!!!
I also thought it might just be some bad RAM, so I took that out and tried to start up again, but that didn't work either.
At this point, I'm clueless and hope that someone might be able to offer some good advice.
Thanks,
Sandie

Answer 1

Just repaired my iMac G5 with complete boot failure, it all came down to capacitors, there was an industry wide use of sub standard/sub spec capacitors at the time the imac G5 was manufactured, due to a manufacturer using a capacitor recipe missing one ingredient, This caused the imac G5's to fail at a much faster rate than they should have done, I had to replace half the capacitors in the power supply and 5 of the higher rated capacitors nearest the power supplies internal vent onto the logic board once this repair was affected, my machine worked perfectly.
take the cover of the back of you imac G5 and see whether your imac version has some led diagnostic lights and check whether the power diagnostic led light lights up properly when started, there are tutorials for this on the web also a light there that indicates whether gpu is communicating with the display properly. all led internal green lights should light up, apart from the right hand one of the four.
with your dark screen and sleep light on symptoms it seems quite likely a surface mount BGA graphics chip failure, but to be honest it could also be a capacitor related issue, if your not into stripping the machine down and soldering capacitors then the machine for you is probably a right off, just try a pram reset boot before giving up, I had similar sleep light no boot scenario on a macbook pro, and a full stripdown got it booting again.
the power supply in the imac G5(als version at least) gets very hot and has no fan of its own and is dependant on the one internal left hand open motherboard fan for its cooling in my opinion it gets too hot, there is also no temp sensor for the power supply to give you an indicator as to how hot its getting, I feel the the heat venting from the overheating power supply internally is what cooked the capacitors nearest it, this is a flaw in the design of this machine. One way to reduce this issue is to perhaps use some kind of extra fan control software to boost the based speed of motherboard fan, whilst at the same time placing and extra entry quality pc fan thin filter foam on intake underneath to prevent any extra dust intake because of the fan speed increase so as to protect the machine from clogging with extra dust and heating the power supply further