Imac G4 15" won't start up

Hi there

I have been a lurker to the site for far too long. I now break my silence with a question because I can't work out the answer for myself!
I have an Apple iMac 700MHz 15" Flat Screen (now 1gb ram) (M8672LL/B). It consistently fails to power up.

I've replaced the PRAM battery. The problem prevailed. I replaced the cable. No luck. A Hardware Test ran overnight, nothing showed up. I re-installed. No help.

I cleared out the dust from the base with a hoover. It worked for a short while, then the problem came back. There is a clicking/tapping sound that can sometimes be heard from the base when it's plugged into the mains and isn't powering up. Resetting the Power Management Unit seems to help power up the mac, but it's never a permanent fix.

Does anyone have any ideas what could be the problem. I love this mac. It's part of the family - it's my baby! I know mac parts aren't cheap, but I really want to save this mac from the dump!

Any help is much appreciated!

Thanks for reading
Luke

That tapping and clicking could well indicate the HARD drive is failing. What does Disk Utility say regards S.M.A.R.T. Status?

Hi Harry

Good idea, I didn't consider that! I just check though, it says 'verified'.

Many thanks for helping!
Luke

The reason I don't think it's the hard drive is you stated the clicking is with the machine powered off. It might be an issue with the switching power supply as I have heard them make various noises and clicks in the past.

Hi dtravis

Yes, the clicking only occurs when the imac won't power up.

My best guess is it's a power supply unit problem, that's a very uneducated guess though! I just wonder if there is an option out there that doesn't involve anything drastic like replacing half the mac's insides to get it working fully again.

If anyone has any ideas, please tell me, I'd love to know what the bloody problem is!

Hey Luke

Did you ever get a solution to this problem you posted? I have 2 iMacs doing exactly the same. I think it's a board called the DC/DC BOARD. I replaced it with a friend's and my computers are booting without a problem. Once I remove the board and put in the original, the clicking/chirping sound resumes and there is no powering of the computer. What I find strange is why the computer works sometimes. Is there some component failing intermittently? And which one is it? Any electronic guru out there?