27 iMac (2012) crashes and requires smc reset to turn on

'Safe mode' works, but refreshing rate is very low, programs like browser refresh all the time. Programs without many GUI elements are ok such as iTerm.

'shutdown iMac during the night' doesn't work for me. The next morning, after using for 1 hour, iMac turns off by itself.

Hi Guys,

Finally, I have got the PSU and installed it yesterday. The process is very straight forward. I would considered it is just medium level installation. I have got the OWC kit, for special torx screw drive(T9, and T10), some adhesive tape and a guitar pick. I also have bought thermal sensor from OWC for the SSD Hard Disk. The turnaround time for the process around an hour.

I have found out the defected PSU is Delta brand. I have replaced the Liteon one. It works quite well, but need to observe it a bit more . I will do a further report about it. In addition, I have also installed the Samsung SSD as the hard drive. I need to create a fusion drive with the default factory SSD. It shouldn't be too hard.

These are the photos taken last night.

https://www.flickr.com/photos/146342873@N02/sets/72157674444595115/

lune-cheung,

Awesome work on this. I have been following this for a long time and still have the issue but was hoping to see someone take the leap and do it right I agree replacing parts with bad parts was always my take on it too. Hey can you email me the correct items/tools please striper134@gm**l.com I would like to order all parts today and get this finally finished so I can use this expensive paperweight for anything other then surfing the web for 15 minutes.

Hi FalseAlbie,

Thanks for your compliments. I better share the parts we should need for the fix and upgrade.

Removing the the Screen tools (if you are NOT upgrade with SSD)

OWC General Servicing Kit

https://eshop.macsales.com/item/OWC/DIYIMACGEN/

Power Supply Unit

Liteon - 300W PA-1311-2A
https://www.aliexpress.com/item/New-Original-300W-PA-1311-2A-Power-Supply-For-Ap ple-iMac-27-A1419-2012-Year-661/32531015…

SSD (Optional)

Samsung SSD or Whatever SSD you want

newertech adaptadrive - https://www.bhphotovideo.com/bnh/controller/home?O=&sku=798867&gclid=Cj0KEQjwsai _BRC30KH347fjksoBEiQAoiaqsWuimAWES6w39JRS_Vt0QzxaiK2pDY3wNlsYQiLA0wMaAodE8P8HAQ& Q=&is=REG&A=details&pcur=AUD

OWC In-line Digital Thermal Sensor for Hard Drive Upgrade (All the tools and thermal Sensor for apple hard drive) - https://eshop.macsales.com/item/OWC/DIDIMACHDD12/

I'm another late 2012 27" i7 iMac with 16GB DDR3 RAM and NIVIDIA GTX 680MX 2048 Mb graphics card owner who is experiencing these random spontaneous shutdowns. Usually when I'm doing OpenGL renders, but occassionally when I'm doing nothing.

The problem started 2.5 years after purchase and progressively got worse. The local Apple dealer couldn't find anything and for 4 months afterwards over winter the computer has been fine. The problem has started again now notwithstanding that the ambient internal day time temperature here is mostly less than 20°C and lower than 10°C at night. The AHT I did the other day says everything is fine.

I am losing work and time and I am very unhappy that a relatively expensive computer looks like it is no longer usable after just 3.5 years.

Like others I would be happy to pay to fix the problem if I knew for sure what the fix was. I am not prepared to gamble on Apple's current solution of lets progressively try replacing components in the hope that will cure the problem though.

Apple need to step up to the plate and tell us how to fix the problem.

Here in Australia products have to be fit for purpose.

I can't see how a computer that starts failing on a regular basis in jus 2.5 years can be deemed fit for purpose.

I have been trying to test stress the computer by intensively using the rendering of a different 3D program to my normal one.

On a couple of occasions I had a brief buzzing sound from the left hand side of the computer.

After three new logic boards, Apple replaced the power supply in ours back in April. The machine has been trouble free since then.

We were about 20 days out of warranty at the time, but they decided to do the repair for free since we'd brought the machine in before the warranty expired.

Well, I did it! Changed out the Delta PS for a Liteon, now we'll see if the fix works!

For one thing, the screen is much brighter. I might have to adjust it down a bit.

Hi Hank, thanks for your update, and you confirmed you had a Delta PSU before.

Looking forward to hear from you again.

Funny thing with the screen though, probably the least worry right now.

Just a report update. I have replaced the Liteon PSU for 2 weeks. I haven't experience any problem.

I do agree Hank K, the screen is a bit brighter with the Liteon PSU.

I got mine replaced approx. 2 months ago by Apple itself. I'm not sure what PSU they put in but it's all safe and sound without any shutdowns

Hi Omoot,

I had my PSU replaced by Apple before. They actually wouldn't replace different parts for you, I have asked one of the Apple Technician who replaced my PSU before.

They will still put the original Delta one in your PSU.

My PSU replaced by apple about 9 months ago( January 2016) , which was still under warranty. However, the shutdown issue happened again around (June).

I thought they have both Delta and LiteOn ones in their inventory and it's just pure luck what you'll get. Am I wrong? If it happens again I'll try to get a LiteOn one

I've been using iStat to see if I can discern any temperature or current anomalies just prior to a shutdown from the graphs it produces. I can't see any and I'm beginning to think that those that are saying it is a fault in the power supply units might be right.

I can't afford a new computer at the moment so I will probably have to punt on getting the PSU replaced by the local Apple Shop in the hope that will fix the problem. If it doesn't fix it I will seriously think about going to the dark side.