Hi everyone. I have lost count of how many threads I have read on this wonderful forum over the years but I haven't ever actually started a thread before, until now! This is a very strange fault and I am hoping someone might help me guess what to replace next!
Mid 2011 iMac 27"
It shuts down every time I boot it up, but only when the progress bar gets around 2/3 of the way across, and I think this has just given me insight into what the fault might be, or at least why it's happening, more on that in a sec!
I have replaced the HDD and PSU, so those two are definitely good. The machine has no data on it, all backed up on clone drives and TM.
I can get to recovery but it powers once i start using it. Ditto for booting from external bootable installer USB, it crashes half way through booting. External hard drive (clone) does the same, the machine just refuses to get all the way through the progress bar. But here's what I think I have just discovered:
It seems to do it ONLY when the screen brightness suddenly increases. Not sure how many people have spotted it but during progress bar it's a kind of dim grey, then just as the bar speeds up to completion the screen brightens up just prior to giving a login box for the user to sign in. I never get quite that far as it blinks and powers off (restarts). I think it's this sudden draw of power for the screen, or something else related to the screen output which is causing the power to trip. It's definitely not the PSU (I was sure it would be) as that has been replaced so I know that's good. Likewise the HDD is fine for definite. I did run AHT before I wiped the hard drive (I wiped it and installed High Sierra by taking out the HDD and putting it in a desktop dock connected to another iMac, then re-fitted). AHT reported no faults at all.
I am no tech, I will get my hands dirty when I feel confident enough though. Does anyone have any idea what component could be causing this issue?
OH and BTW - VERY interestingly, I tried to confirm my suspicion that it's screen-related....
I unpluged the LCD from the machine, then powered it up. It booted up properly this time and even though I couldn't see any display of what was going on, I am 99% sure it went to the login window as it never powered off at all, I left it running for 15+ minutes and it sat quite happily spinning away. When the LCD is connected the machine doesn't stay on for more than a couple minutes just long enough for the boot sequence to get near the end of the progress bar then poof, off she goes. Doesn't do that without the screen in.
I dont have much money, hence why I get offended when people on the Apple forum say "just replace it, it's too old now"! Which, I might add, is utterly ridiculous. This machine has 32GB ram, 2 TB HDD, and I have used it for many years 24 hours a day doing some VERY heavy work, it has never once slowed down or given me any performance concerns at all. To say I should throw it in the trash and go and get my wallet burned at the Apple store, yeah, not for me! I like to make as much use of things, especially great things like this brilliant machine (until now!) as I can. And there's plenty of life in this if I can solve this issue. IF it was the logic board I would break it up for parts on ebay to get a bit of cash. But I am sure the logic board is fine, and I will soon get a cable to try an external screen which would really confirm my suspicions about the LCD!
Any help, tips, thoughts.... all very much appreciated
Thanks
Mid 2011 iMac 27"
It shuts down every time I boot it up, but only when the progress bar gets around 2/3 of the way across, and I think this has just given me insight into what the fault might be, or at least why it's happening, more on that in a sec!
I have replaced the HDD and PSU, so those two are definitely good. The machine has no data on it, all backed up on clone drives and TM.
I can get to recovery but it powers once i start using it. Ditto for booting from external bootable installer USB, it crashes half way through booting. External hard drive (clone) does the same, the machine just refuses to get all the way through the progress bar. But here's what I think I have just discovered:
It seems to do it ONLY when the screen brightness suddenly increases. Not sure how many people have spotted it but during progress bar it's a kind of dim grey, then just as the bar speeds up to completion the screen brightens up just prior to giving a login box for the user to sign in. I never get quite that far as it blinks and powers off (restarts). I think it's this sudden draw of power for the screen, or something else related to the screen output which is causing the power to trip. It's definitely not the PSU (I was sure it would be) as that has been replaced so I know that's good. Likewise the HDD is fine for definite. I did run AHT before I wiped the hard drive (I wiped it and installed High Sierra by taking out the HDD and putting it in a desktop dock connected to another iMac, then re-fitted). AHT reported no faults at all.
I am no tech, I will get my hands dirty when I feel confident enough though. Does anyone have any idea what component could be causing this issue?
OH and BTW - VERY interestingly, I tried to confirm my suspicion that it's screen-related....
I unpluged the LCD from the machine, then powered it up. It booted up properly this time and even though I couldn't see any display of what was going on, I am 99% sure it went to the login window as it never powered off at all, I left it running for 15+ minutes and it sat quite happily spinning away. When the LCD is connected the machine doesn't stay on for more than a couple minutes just long enough for the boot sequence to get near the end of the progress bar then poof, off she goes. Doesn't do that without the screen in.
I dont have much money, hence why I get offended when people on the Apple forum say "just replace it, it's too old now"! Which, I might add, is utterly ridiculous. This machine has 32GB ram, 2 TB HDD, and I have used it for many years 24 hours a day doing some VERY heavy work, it has never once slowed down or given me any performance concerns at all. To say I should throw it in the trash and go and get my wallet burned at the Apple store, yeah, not for me! I like to make as much use of things, especially great things like this brilliant machine (until now!) as I can. And there's plenty of life in this if I can solve this issue. IF it was the logic board I would break it up for parts on ebay to get a bit of cash. But I am sure the logic board is fine, and I will soon get a cable to try an external screen which would really confirm my suspicions about the LCD!
Any help, tips, thoughts.... all very much appreciated
Thanks
