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All replies
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Helpful answers
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Jul 30, 2016 7:08 AM in response to Glasguyby ElBartolomeo,mmmh interesting....I will follow your post clean tests!
if this is the problem i will bring my iMac to apple assistance
for cleaning.
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Jul 30, 2016 7:19 AM in response to ElBartolomeoby FranFox,I'm not sure that full cleaning solve the problem. I wrote few days ago about that my suggestions for the problem would be overheating but after some days and more tests I can't confirm that. Also I've tried to unable the turboboost of the processor to reduce the temperature and it works but as I said I'm pretty sure that heat is not the main problem.
By the moment the only way to stop shutdowns has been disconnect the iMac from the charge cable during the night, since I'm doing this every day I'm not having any shutdown even if the temperature of the computer is high.
I've start thinking that could be some electrostatic charge in some of the components. That would explain that after disconnect the cable for long periods (some hours) the shutdowns disappears. Could you try this method and post the results?
I hope it helps
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Jul 30, 2016 7:46 AM in response to FranFoxby Glasguy,Just to confirm now that after cleaning the system and applying thermal paste the iMac shut down after 7.5 hours.
So the problem still persists. Next action is to try a new power supply. On inspection of the old power supply, it does not look great as it has white ingress on parts of it. Possibly dirt and humidity may have effected the power supply.
At the moment I'm unsure about electrostatic discharge causing the shutdowns, I think there is possibly a relation between the dust insutlating and damaging components in the iMac. My power supply does not look that great on inspection. I will replace power supply and test and post back my findings.
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Jul 30, 2016 8:31 AM in response to Lagoiskiby mattwithcats,Those temperatures look a little funky to me.
Looks like they say Celsius, but are actually Fahrenheit...
100 Cº is 212 Fº, the temp where water boils....
I still say this is a power problem with the 95 watt processors, and overheating...
Jack up your CPU fan speed and see what you get.
My 21 inch I5 running at 2.5 is at 90 Fº, and I have noticed it gets to 110 - 120º, unless I override the fans, which I have done...
Also look for stray processes eating CPU cycles up....
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Jul 30, 2016 8:49 AM in response to mattwithcatsby ElBartolomeo,before the shutdown my imac's fan don't go up with rpm
when the problem didn't exist i could play with heavy games and when cpu temp grow up, also the fan speed up the rpm...
now the shutdown sudden came without previous speedup of the temp....
probably temp is not the problem...
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Jul 31, 2016 4:46 AM in response to mattwithcatsby Beolion73,That is a new theory, and quite interesting, especially if this is the cause. Why make you believe that the problem is related to the 77 watt TDP? What CPU models are 77 watt TDP?
My CPU is Core i5 (3470), but the problem is that a CPU change is quite difficult and relatively costly.
Would certainly be helpful if we could get any statements from Apple soon.
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Jul 31, 2016 12:19 PM in response to Beolion73by mattwithcats,Look at the processors offered for Late 2012 iMac,
https://en.wikipedia.org/wiki/IMac_(Intel-based)#Unibody_iMac
Intel i5
2.7, i5-3335S (low power, 65 watt)
2.9, i5-3470S (low power, 65 watt)
3.2, i5-3470 (77 watt)
i7
3.1 3770S (low power, 65 watt)
3.4 3770 (77 watt)
The vast majority of people having problems are using either the 3.2 i5 or the 3.4 i7, both 77 watt, and have a 27 inch screen.
Looks like retail for a used i7 3770S or 3770T (45 watt) is $200,
http://www.reusetek.com/intel-core-i7-3770s-sr0pn-3-1ghz-5gt-s-lga-1155-processo r/
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Jul 31, 2016 12:22 PM in response to mattwithcatsby mattwithcats,Knock, Knock, Apple...
Knock Knock...
Major problem found here.....
You need to adjust the temp sensors responsiveness....
CPU's need to be cooler....
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Jul 31, 2016 1:12 PM in response to mattwithcatsby NickFromLE,I dont think that all of the related issues in this post comes down to just one issue.
My temps are not to high, 65-70 in normal use.
Today I had another random shutdown by simple opening Safari. I clicked on the Sarafi Icon and the screen went black and the system was down. I had to wait 10mins before I was able to restart it.
I do have the i5 3,2 - that would fit in the profile but I also had 95 degree within games without problems. It always occurs when Safari is in use. When I switch to Firefox everything is fine. I just dont like Firefox on my Mac...
I think this is a Software- and Hardware Problem.
Just my 2 cents.
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Jul 31, 2016 7:24 PM in response to MissionCompleteby stjohns,Hello Mission Complete,
So have you experienced and shutdowns since you had the power supply replaced?
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Jul 31, 2016 11:55 PM in response to stjohnsby ElBartolomeo,why it shutdown when you try to reset pram?
i don't know if it could be only a software problem....
anyone has tryed to install maverick?
I have this problem from some update ago of el capitan....
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Aug 1, 2016 8:23 PM in response to ElBartolomeoby lune-cheung,I just go the random shut down happen again on my 2012 iMac 27inch, since the apple shop replaced the Power Supply 6 months ago. It shutdown 3 times last night. I am very disappointed with this product. Apple should provide replacement program for that.
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Aug 2, 2016 12:04 AM in response to Lagoiskiby Glasguy,Done some further testing using the Apple Service Diagnostics, ASD OS and ASD EFI from a bootable HDD whilst waiting on delivery of a replacement power supply.
I started the tests using the ASD OS and within two hours the iMac shutdown. Repeated the ASD OS test and the iMac shutdown again . During each successful loop ( before shutdown ) of the ASD OS test no faults where found and test reported as a pass.
So after this I ran the ASD EFI test for over 16 hours ( no faults found ) and the iMac did not shutdown. Straight after the ASD EFI test I then ran the ASD OS test and within the first 30 seconds of the test the iMac shutdown, I restarted the iMac and again the ran the ASD OS test and it shutdown again within 30 seconds, tried again and same happened.
After this, the iMac was booted into OS X El Capitan in safe mode and no shutdown observed as yet.
I'm now wondering:
Could this possibly be the power management difference between ASD OS and ASD EFI diagnostic testing hence the sudden shutdowns when using ASD OS ?
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Aug 2, 2016 7:33 AM in response to Lagoiskiby Glasguy,Having now replaced the power supply, I ran the ASD OS test. During the last test where the iMac shutdown was during the WiFi / Bluetooth sleep, wake and standby tests. On this occasion the ASD OS now reports that this has failed.
It seems that the problem has roots with a faulty power supply and WIFI/Bluetooth module. Especially wake, sleep as the power will be directly related with this.
Intresting, folk have commented that the shutdown happens when using safari. So from here my next plan of action is to remove the Wifi / Bluetooth module and test to see if the intermittent shutdown persists.
The old PSU
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Aug 2, 2016 11:45 AM in response to Lagoiskiby Glasguy,I ran a 4 hour ASD OS test this time, but unchecked Bluetooth, Airport. No intermittent shutdown during tests. The test ends successfully. I then decided to perform a PRAM reset to test the Bluetooth and Airport, this time the only error reported is the Wake on Wireless Internal Simulation Standby Test.
I'm more convinced that the power supply is has been the problem. The Wake on Wireless Simulation test is most likely software / firmware.
If I experience another intermittent shutdown on my iMac i will update it on this post.








