Help Me Diagnose This issue.

Discussion in 'iMac' started by squalorvictoria, Oct 23, 2011.

  1. squalorvictoria macrumors newbie

    Joined:
    Jan 23, 2008
    #1
    Came home monday during a thunderstom with a lot of lightning. Quite sure some lightning hit rather close to our house. Checked the iMac and it wasnt turning on, simple enough reason - the breaker had been switched. Switched the breaker and turned the mac on, it chimed, hard drive fired up, superdrive spun, all looked good. Except, the screen was not turning on. Turned it on and off a few times and it kept doing the same thing, i noticed that when i pushed the volume buttons on the keyboard, it made all the sounds it should, different noises were made depending on what keyboard buttin i pressed, as best i can tell, everything booted up and was working properly other than just getting no display. I have a external monitor hooked up and was getting no display on that either. I checked on my macbook and the imac was showing up in the shared directory for screen sharing and i was hoping i could connect to it and see the screen and see how it booted up, but it kept just saying connecting....... i assume i needed to give permission to share on the imac which was not possible since i couldnt see. Turned it off again and went to turn it on and got nothing, now it wont bot or chime or anything.

    Does this sound like a logic board issue, or a power supply issue. i am really hoping it is just the power supply has gone bad. We have had some electrical problems in our house where the breaker will trip randomly several times a week, which of course is causing the imac to hard reset quite often undoubtedly putting a lot of stress on the power supply. Ive already had to replace the hard drive which i attributed its failure to the constant hard resets.

    So, im just unsire if it could be that or it could be a lightening strike which hit the logic board. The imac is on a surge protector, but our cable modem wasnt, and the cable modem is not working at all. the cable modem was connected directly to a time capsule (on the surge protector) which in turn was connected directly to the imac. Could a power surge have gone though the modem and into the computer through there? The time capsule is working fine.

    Ive already dropped the imac off at a authorized repair center, but they didnt have a power supply to swap it out with so they had to order one so its going to be awhile before they can check that. Just wanted to get some opions here on what it could be.
     
  2. Nishi100 macrumors 6502a

    Joined:
    Mar 27, 2010
    #2
    I don't know about the display not turning on, but I can tell you that the surge couldn't have gone through the Time Capsule, as - even though there would've been a large PD from the iMac's output to the TC - the resistance would've been very high in the iMac and almost all of it would've been taken to a low enough voltage (the resistance of the modem and TC) for the iMac's internals to take, even if there wasn't a diode near the USB ports (prevents current flowing that way).
     
  3. squalorvictoria thread starter macrumors newbie

    Joined:
    Jan 23, 2008
    #3
    Thaks for that info, makes me feel a little better that it may not be a logic board problem. We'll see.

    Anyone else got any ideas? Its a Mid 07 iMac 24" if that matters.
     
  4. Detrius macrumors 68000

    Joined:
    Sep 10, 2008
    Location:
    Asheville, NC
    #4
    The fact that you have no internal or external video sounds like the video card to me. The fact that you have the iMac connected to a surge suppressor does not mean a surge didn't go through it. Those things have a limited lifetime rated in joules, and once that much energy has been dissipated, they only work as a power strip. I've seen surges take out RAM modules and graphics cards, leaving everything else functioning. It's easy for a surge to take out a hard drive, since it has its own direct power cord.

    I'd recommend investing in a UPS.
     
  5. VulchR macrumors 68020

    VulchR

    Joined:
    Jun 8, 2009
    Location:
    Scotland
    #5
    I'm not sure if it is the same kind of problem, but on an Apple LCD screen from the same year, I had problems recently with the display going blank. Everything else appeared to work. I did some Googling because the power button was flashing an error signal and it turned out to be a transformer circuit board that could be replaced (power supply component). In general I have noticed many electronic devices built 2005-2010 failing (including a laboratory apparatus that literally popped, sizzled and smoked the first time I plugged it in) because of power supply problems. I wonder how good the quality control was in Asia then....
     
  6. Detrius macrumors 68000

    Joined:
    Sep 10, 2008
    Location:
    Asheville, NC
    #6
    I think your factors are a bit off there. The Mac Plus had an 8MHz processor and a maximum of 4MB of RAM. RAM is now measured in GB, which is 1024 times as much, and processor speeds are measured in GHz, which is 1000 times faster. On top of that, processors do significantly more in one cycle than they did back then. The Mac Plus could do .7 MIPS. The Quadra 840av could do 35 MIPS, so it was 50x faster. I think if you add a handful of zeroes at the end of your numbers, you'll be closer to the truth.

    The TI-89 graphing calculator that at this point is about 13 years old is roughly the equivalent of the Mac Plus, since it actually has a 68k processor in it.
     

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