iMac in the oven at 390°, now it won't turn on.

Discussion in 'iMac' started by ActionJacksonHern, Feb 21, 2018.

?

What should I try?

  1. Blow dry the PSU

    14.3%
  2. Buy a new PSU, it's shorted out.

    14.3%
  3. Sell for parts, it's dead.

    85.7%
Multiple votes are allowed.
  1. ActionJacksonHern macrumors newbie

    ActionJacksonHern

    Joined:
    Nov 17, 2015
    Location:
    Coeur d'Alene, Idaho
    #1
    I have a iMac 2011 27", EMC 2429, 2.7GHz, MC813LL/A, and I'm having problems. First one was the display shutting down randomly, likely due to the common problem with this iMac that Apple did recall here. After days of research, I found the most common fix (after the recall expired) was to actually take the faulty GPU and bake in the oven. Many articles and YouTube videos available here. Apparently almost every person that tried this got it working. So I did the same, baked at 390°F for 10 minutes.

    Problem is, once I put back in the baked GPU and everything back together, the iMac won't fully power on. I hear the fans run for about 0.5 seconds then shut down. I opened the iMac again to look at the diagnostic LEDs (here). The first one is always illuminated, implying that "trickle voltage from the power supply unit (PSU) has been detected by main logic board, the power supply is functioning, and LED will remain illuminated while iMac is plugged in." But as I try to power on the iMac, the second LED will flash on for that same 0.5 seconds as the fans power, but then turn everything off. It will repeat this cycle every 5 seconds. Start up loop.

    I've reset the SMC (here) on the iMac by unplugging, holding the power button for 5 seconds, release, plug in, then power on. Only difference was the fans stayed on about 0.2 seconds longer now, but still went into that power up loop.

    I can't see if the 'baking the GPU' actually worked for me because the iMac won't get to the stage of turning on the LCD display, which would also be signified by the 3rd and 4th LED.

    I feel it is a short or something wrong with the PSU. It's giving some power, but unable to give enough for full start-up. It was working before I did the GPU teardown, so I'm wondering if I shorted something in the teardown. Some people have mentioned a fuse here, haven't found it. I also have not tried taking a blow dryer to the PCU yet (here), as some have suggested. Any ideas?
     
  2. Razzerman macrumors 6502

    Joined:
    Sep 11, 2007
    #2
    Hello there,

    The 'normal' symptoms for a failing graphics card on these imac are vertical stripes, distortion etc. I'd suggest that the whole screen going off could be a different issue. No harm in doing the reflow, and your time & temps look fine.

    It might be worth looking at this thread about the backlight inverter - https://www.ifixit.com/Answers/View/106622/Backlight+turning+off,+inverter-board+changed

    I'd vote for 'some other symptom' ;)

    Cheers,

    Razzerman
     
  3. ActionJacksonHern thread starter macrumors newbie

    ActionJacksonHern

    Joined:
    Nov 17, 2015
    Location:
    Coeur d'Alene, Idaho
    #3
    From the internal Apple note on the GPU issues this iMac had, one of them were commonly black screens. I also tried two different functioning inverters and that was not the issue. Thanks for the ideas though.
     
  4. philosoraptor1 macrumors newbie

    Joined:
    Jun 2, 2011
    #4
    For a moist, tender iMac, always bake at 375 for no more than 7 minutes. Lesson learned.
     
  5. Fishrrman macrumors P6

    Fishrrman

    Joined:
    Feb 20, 2009
    #5
    I guess you over-baked it. ;)
    Time for a new iMac.
     

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4 February 21, 2018