So I wanted to post on MacRumors as I read the site often for both news and forums, and I wanted to get the opinions of some of the folks on here who know their Apple hardware well. My issues started around 3 weeks ago with my Mid 2011 27" iMac. It is the 3.1GHz i5 Sandy Bridge generation with the AMD Radeon HD 6970M w/ 1GB video ram. I'm the only owner and purchased it in May of 2011. The issue is rather bizarre. During nearly any type of activity, the machine will hard power off. I've repeated the issue surfing Safari, playing movies, word processing in Word or Pages, etc. Most commonly the issue is easiest to repeat in Safari when playing a streamed video. It literally acts as if the machine lost complete power. Early on it almost sounded like a short on the logic board or power supply. You'd hear a discharging "Pop!" noise when it occurred. Then following the hard power loss the machine would "reboot following power loss". My machine has been serviced on 2 other occasions. I was plagued in a bad batch of 27" display panels where the gray "blotching" would occur on the panel. I'm on my 3rd panel, and both of the replacements occurred under the 3 year AppleCare extended plan. I started my barrage of tests. I swapped out my OWC RAM for the factory RAM, ran the AHT that came on Disc 2 of the installation DVDs. Ran the old Tech Tool Deluxe that came with my AppleCare purchase, and everything came back clean. So I then started my google research and stumbled across a repair program for 27" iMacs with the Graphics card that my own model contained (https://support.apple.com/en-us/HT203787). So knowing that I was well out of warranty and that my machine didn't possess the exact same symptoms as described in the article, I called AppleCare anyway. My conversation with AppleCare on Sunday Dec 4th, started with a Level 1 tech, who the poor girl, was incredibly confused by all of my technical speak and quickly escalated me to a Tier 2 Advisor. This guy very clearly knew his stuff and was a nuts and bolts guy like myself. He agreed something was wrong and wanted to see diagnostics get run on the machine and specifically the graphics card, since the issue could most frequently be replicated during streaming videos. He created a Genius Bar appointment for me at my local store in Lancaster, PA and created an CS Code(CR) Warranty exception on my behalf. Believe it or not, I had no idea what the CS Code was until I did some research. I'm VERY grateful to this Advisor, as he's likely saved me a ton of money. On Monday evening Dec 5th after work, I took the iMac to my Genius Bar appt. I got a great genius, who again was a nuts and bolts guy like me, and we were able to speak very frankly and matter of factly on the issue. All firmware and diags run on the spot came up clean, except for my hard drive which S.M.A.R.T. status showed as failing. We then allowed MacOS to boot and I was able to repeat the issue for him twice on the spot. Once while playing a video, and then the machine went into a reboot loop where something was obviously wrong. His feeling was that a short was likely occurring on the Logic Board and wanted to replace the logic board and hard drive as well as run ASD OS and ASD EF tests to attempt to find other issues with the Logic Board and/or Video Card. After the 4th Day, Friday the 9th, I received a call from Apple asking if they could have my iMac a few days longer. I obliged and received a call on Sunday night the 11th at 7:30p that my iMac was ready for pickup. Considering that the store closed at 8p, I had to wait until after work last night to go get my iMac. I went and picked it up. They noted that they replaced the Logic Board & Hard Drive at $701.73 and no cost to me, thanks to the CS Code. I took it home, plugged it in and started through the macOS setup. On the language selection screen, the machine goes dark and reboots. My heart sank. I chalked it up as a fluke thing, and attempted to complete the macOS setup. Setup finishes, I open safari and jump to weather.com and play a random video. The ad finishes, and the video starts, and dark screen. I'm devastated. I call in and work thru the infuriating process of what is the Apple Retail IVR. Finally asking to speak to a store manager and getting through. I explained my case, told him they didn't fix the issue and that I want to bring my iMac back to them. He agreed and said that I could drop it back off. So I drove my 25 min back to my local Apple Store and handed them back my iMac to begin day 8 of repairs. The specialist I gave my Mac to said that they're going to order additional parts (including a graphics card) and it'll be a few days. I'm really frustrated. No question, Apple is doing me a solid here in attempting to fix this. But a week without my Photos library, and the ability to edit them, my main home media server and streaming library, it stinks. Has anyone else seen this issue or know of the symptoms and what it may be? I'll definitely update this thread once I hopefully get a resolution. Its been a great machine despite now being on its 3rd display panel, 2nd hard drive & 2nd logic board.