IMac shutting off, Mobo, PSU, overheat?

Discussion in 'iMac' started by Biciclettapc, Jun 22, 2008.

  1. Biciclettapc macrumors newbie

    Jun 22, 2008
    Needs some help or suggestions.

    I have a 20" Imac, PPC running tiger. Just in the past few weeks it will just shut down while being used. I thought it might be a software issue, since typically I run Firefox for a browser, but it will do so with anything up or nothing up even at log in screen.

    I am very comfortable inside the computers, I have this apple, a Win laptop for work and (2) Linux Ubuntu boxes I have built up from scratch. SO I take the back off the Imac and clean it out, thinking it possibly overheating, since I had read several issues on G5 and heat issues. No luck..... but the fans didnt seem to spin up well.

    I contacted a local repair shop and discussed with them, they seemed to lean towards PSU and loaned me a PSU from a 17 they had to try first. No luck, still shut down.

    Back to heat. I actutally took the back off and ran the computer with a box fan pointed at the back . Ran Itunes, Firefox, watched a DVD and opened up anything else I could all at the same time to run the CPU up, while the fan blew into the open back. Seemed to work fine for the 3 or 4 hours it ran. SO, I replaced both fans at a cost of $43 :eek: Seemed to work now for about 3 days, ran fine with no issues.

    Well its started again.....:mad: It now has started shutting off within a couple of minutes of turning on. This morning it might have been on for less than 2 minutes, which should rule out over heating.

    I have ran the diagnostic disk and it comes back clean. Oh computer didnt shut off in the full run of diagnostic, but this was before I replaced the fans 3 days ago

    Is it a Motherboard ? :mad:

    Not sure if this is possible but it did update system software right before it started happening.

    I have not reinstalled OS yet, but may resort to that.

  2. bigrell486 macrumors 6502


    Jul 10, 2006
  3. gehrbox macrumors 65816


    Jul 5, 2007
    Have you tried disconnecting all USB devices except mouse and keyboard? They can cause issues. There was also a reported problem with Microsoft mice by somebody around here. That and some other suggestions are available in the following thread:
  4. ihabime macrumors 6502

    Jan 12, 2005
    It definitely doesn't sound software related to me. There is a specific problem with first gen G5 iMacs and power failures, you can check your serial number here to see if that applies to yours.

    If it's not that I wouldn't rule out overheating, if the heatsink had come loose or wasn't in direct contact the G5 can overheat pretty quickly. You could try running a temperature monitor to track it.
  5. Biciclettapc thread starter macrumors newbie

    Jun 22, 2008
    Well, currently trying another outlet in the house running off a drop chord. As of right now its been up and running for more than 1 hour. Ran the extended diagonstic which took 59 min with no problems. Funny the fans run wide open during that but under normal run mode I can hardly hear them and barely feel the airflow from the back. This was true with old fans and new ones currently installed.

    This unit is about 4yo, and the first owner had the psu replaced, I imagine under warranty. I think the mobo has a possible warranty but being I think its too old to fall into that replacement. But, diagonstic show no logic board issue or anything else.

    Did do a Pram reset this morning, but it shut down after that. Same with a SMU reset, but I think that resets with each power down too.

    As far as temp monitors, currenty the cpu is at 58.7C and HDD is at 48

    as far as USB devices. Well, same mouse and keyboard have been plugged in for 6 months. It is a MS mouse, I do have a BT apple mouse, but my wife hates it, says its too heavy and doesnt work real well (I agree) Thats the only 2 usb devices, only other is a ethernet cable


Share This Page