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I recently bought a 27 inch iMac 2011 for cheap that didn’t start according to the previous owner. When i opened it i immediately noticed that the hard drive and ram was missing. So i inserted two sticks of compatible ram and plugged it in, seeing that the first of the diagnostics LED lit up. When i press the power button however nothing happens except for the PSU making some kind of pulsating, humming sound. Is the PSU broken or is there anything else i should try before ordering a rather expensive used one to try and replace? The sound coming from the PSU can be heard on this link: https://drive.google.com/open?id=1k9Ev05… I greatly appreciate any answers and help! Update (11/16/2018) Hello again! First of all i would like to thank you for your answer. I ordered the replacement PSU but when i installed it today nothing changed. Same symptoms as before. Do you have an idea what to look for next?
Based on that sound recording you provided I think you may have a broken PSU. I have worked on that model iMac before and I have never heard such an awful sound come out of a PSU in that iMac in my life. iMac Intel 27" EMC 2309, 2374, 2390 or 2429 Power Supply iMac Intel 27" EMC 2429 Power Supply Replacement
