In retrospect, I let myself go up a blind alley all because of Apple's claim that this was a RAM error.īTW, I located the shorted cap on the jack with my thermal camera. How does a missing S4 rail equate to a RAM error? Of course, you won't realise that there's a short when you take the board out to check everything, because J6500 will be disconnected.

This comes from the PP3V3_S4 rail, so that's a pretty important rail to remove in the power sequence. From the 320-3298-A schematic, this short was on pin 17 (PP3V3_S4_AUDIO_DIG).

I started metering the board on the rear of this jack, and found a couple of caps shorted. When disconnected, the iMac sprung to life. Well you know where this headed, the RAM was not the cause, as replacement RAM didn't work, and the RAM fitted worked in another machine.Ĭut a long story short, the fault was not on the motherboard itself, but on the headphone jack (J6500). So I got this 2012 27' Apple iMac come in with a single beep every 5 seconds. But I thought I'd post this fault as it may save some people a lot of freaking time. I don't have too much troubleshooting experience on iMacs, as they are such a PITA to work on.

Macbook pro 3 beeps every 5 seconds