Chosen Solution
Hi everyone. My iMac 27” Mid 2010 has a continuous buzzing noise from the back of the upper left corner. It is continuous now, but at the beginning it was lower, and sporadic, from time to time. After a recent weird issue (corrupted RAM module, Time Machine external drive got unusable), the noise is now higher, and never ceases. I’ve extensively read all threads and info about this type of noise, and most answers do point to a possible PSU issue. Or maybe the backlight board. Since a new PSU is around 140 €, has anybody experimented this issue? Any advice? I can provide a video to further understand the problem. The computer has run flawlessly for the last ten years… This is the first and only issue to date. Thanks in advance.
Things I would do is make sure the AC outlet is properly wired using a simple AC tester like this one 3-Wire Receptacle Tester. I would also check the breaker panel to make sure the main grounding cable is in good shape it’s either a bare heavy gage copper wire or one that is colored green which connects to your building water pipe or grounding rod/s. Make sure the connections are not corroded and the connections are metal to metal. You may want to get an electrician look at it if you think its too much for you to deal with. I would also recommend making sure you have a good surge suppressor or look at getting a good UPS. A power disruption could explain your RAM and TimeMachine issues which a good UPS would prevent. Sadly, a power surge could have damaged your power supply which can explain the buzzing noise. I’ve replace quite a few power supplies which buzzed. But you really need to start at the outlet making sure you’ve got things covered there before you replace the power supply. Update (03/12/2020) We don’t have a guide for your system but the 2011 is exactly the same. Here’s that guide: iMac Intel 27" EMC 2429 Power Supply Replacement and here’s the needed part iMac Intel 27" EMC 2309, 2374, 2390 or 2429 Power Supply and here’s a used one which is a bit cheaper iMac 27" Power Supply, 310W (09/10/11) As your brightness alters the sound I would also recommend inspecting the LED driver board. Here’s the guide to take it out iMac Intel 27" EMC 2390 LED Driver Board Replacement and here’s the needed part iMac 27" LED Backlight Board. Check the coils on the back side for damage.
