iMac Shuts Down after First Chime & Apple Logo appears
Hi all! I’d appreciate any advice on this super annoying problem I’ve encountered with a project iMac I’ve been working on. Long story short, I picked up this iMac on OfferUp for $15 with the only “issue”, according to the seller, being that the LCD screen was somehow broken. Upon further inspection, the connector to the logic board for the LVDS cable was ripped from the board and was completely missing. Here’s what I’ve done so far:
• Replaced the logic board with an identical one that HAS this missing connector
• Replaced the CPU/re-thermal-pasted it into the new logic board
• Reconnected EVERY bit of cabling and all of the connectors inside the unit
When I power on the machine, each of the “good” diagnostic lights turn on, and the screen works – YAY! However, the machine will turn on, chime, give me the Apple logo with a status bar, and then within 5-7 seconds of chiming, it spontaneously shuts down. I suspected the hard drive, so I created a bootable USB installer of High Sierra and booted the machine into Startup Manager so I could choose the USB; this works, but the computer still shuts down before I’m even able to select the USB.
I’m now considering the power supply, but I’m not fully convinced that this is the problem because the machine is clearly getting power; does anyone have ANY idea what the issue could be here? I’d appreciate any insight at all, thank you so much for reading!
EDIT: Please see the following photos (the first is the original PSU that I pulled from the iMac, and the second is the PSU that I purchased on eBay for my particular A1311 model).