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I upgraded the RAM and hard drive in our iMac a month ago. I was meticulous about re-connecting components and wires when I was working inside of the chassis, however, I fear I may have missed something. When I finished, I found that there was no audio coming from the internal speakers. I also noticed a red light coming from the 3.5mm audio jack on the back. System Preferences do not show anything but a Digital audio output. I can connect analog (external) speakers to the iMac, and they do play, however, the Left/Right balance only raises/lowers the volume in both stereo channels simultaneously (as opposed to raising/lowering each channel volume independently). I’ve tried resetting the PRAM, but still no sound. Could I have missed connecting some wire when I was performing the HD/RAM upgrade, or does the fact that the iMac still plays the startup chime indicate that the internal speakers are connected properly? Also, any idea how to fix?
Sadly your headphone jack cable is either not connected or the cable/connector got damaged. It completes the circuit to the speakers via two switches within it here’s how it works. See if a wired headphone works.
Review this guide iMac Intel 21.5" EMC 2638 RAM Replacement Step 51 to make sure the cable is connected. Disconnect it and inspect the cable and connectors for damage
