2014 iMac 27"
- Single beep on boot
The single beep on boot is caused by a shorted capacitor on the headphone jack. Disconnect the headphone jack and test to see if beep is gone. Remove headphone jack (it is double sided taped on) and test caps for continuity, remove or replace shorted cap. I do not know the value of the cap, nor did I photograph it, but there are only 5 caps on the board and the faulty one was slightly discoloured.