Chosen Solution
When powering on my iMac Retina 5K, 27-inch, Late 2015 A1419 EMC 2834 I get a recurring beep every 5 seconds suggesting a RAM issue which turns out NOT to be the problem. When I detach the Headphone Flex Cable from the logic board (bottom right next to the right speaker) the computer boots normally. Originally the sound went out and there was no Internal Speakers or Headphones option in Sound pane of System Preferences. After much troubleshooting it came down to replacing the Headphone Jack. However after replacing, I’m not able to boot and get a recurring beep every 5 seconds. Only finding a couple instances online, each were resolved by replacing the Headphone Jack - one person replaced it twice assuming the first replacement part was faulty. I’ve now replaced the Headphone Jack three times, each time assuming/hoping the part received was defective. If the Headphone Flex Cable is connected to the Logic Board at startup, LEDs 1 and 2 come on but the computer will not boot, beeping every 5 seconds. The fan also runs at a very high speed. The iMac continues to beep every 5 seconds until being manually powered off. Even then, LED 1 never turns off completely as it does with a normal shut down and the fan continues to run at a high speed. The iMac reboots on its own and only then can it be shut down correctly resulting in all LEDs turning off and the fan stops running. If the Headphone Flex Cable is left disconnected at startup, the computer boots up fine, the fan runs normal and there doesn’t seem to be any issues other than having no Internal Speakers or Headphones option. If after the computer is up and running the Headphone Flex Cable is connected to the logic board, the Internal Speakers and Headphones option become available and connected external speakers work without issue. When I shut down the computer all LEDs turn off as does the fan. However, when I restart I’m back to getting a beep every 5 seconds. I’ve only found a couple of the same instances online and each were resolved by replacing the Headphone Jack. One person replaced it twice assuming the first replacement part was faulty. I’ve now replaced the Headphone Jack three times, each time assuming/hoping the part received was defective. Although not mine, a video showing the exact issue I’m having can be seen here: https://www.youtube.com/watch?v=U6CT2lmr… Thanks in advance
Apple doesn’t offer this part or the cable as a standard replacement. Although the Headphone Socket and Cable replacement I ordered three different times was specified to work with A1419 it does NOT work with the Late 2015. Apparently 2014 and 2015 use a different part than prior years although I don’t know the specifications. The solution was to order a recycled part, specifically, the one Dan mentioned: 27” Mac Headphone Socket and Cable. Upon installation the computer booted without issue, the Headphone Port is 100% functional and I’m not seeing any further repercussions.
At this point you likely had a bad logic board connector. I would carefully inspect the contacts within the connector to see if one is damaged. Apple doesn’t offer this part or the cable as a standard replacement. As such what you’ll find is a recycled cable as an example: 27” Mac Headphone Socket and Cable and if the logic board is damaged it will need service by someone with the deeper micro soldering skills and access to the needed part.
