Model A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor

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Buzzing sound from the LED backlight board

My 27 inch 2011 iMac started to buzz in the top left corner (when facing the screen). It was silent for the first 5 years I had it.

Then the buzz started. The buzz sound increases as I raise the brightness.

I changed the PSU. The buzz came back after 2 days. Then, I changed the LED backlight board and the buzz came back after an hour...

There is nothing left to change! If someone finds a fix, please let me know.

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Hows the houses AC power? Do you have a UPS or a surge suppressor?

You may want to check your buildings ground as well as your outlets something maybe leaking to it or the grounding rod is worn out.

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@indydan just to clarify the Buzzing sound does come from the LED backlight board? the sound changes with the brightness?

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Dan. It has nothing to do with the AC power. Iam also an audiophile, so I have Oyaide receptacles and Shunyata gear for filtration distribution. Ok, so the Imac is plugged not into Shunyata gear, but a Monster power bar.

After more digging and an email exchange with the vendor who sold me the LED backlight board, it seems the problem is the logic board. the logic board is faulty, so it makes the power supply and LED backlight boards work too hard.

Bottom line is I have to change the logic board.

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Oldturkey. yes the sound comes from the LED backlight board. but the LED board is making the noise because of a faulty logic board.

The vendor who sold me the LED board said this was a problem with these iMacs, and that even the Apple store geniuses were not aware of the problem... He even offered to take back the LED board and refund me.

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I did not want to pay for a logic board. Luckily, one of my colleagues wanted to sell her 2010 27 inch iMac. It is model 11,3, the one just before my 12,2 27 inch 2011 iMac.

She bought it and used it as a paperweight for 5 years. It is in mint condition. It cost me less than a logic board! I transferred my solid state drive into it, and then migrated my stuff onto it. Works great!

Theoretically it has a slower CPU, 3.6 dual core VS the 3.1 Quad core in my noisey faulty 2011 27 inch iMac.

In use, I perceive no difference in speed.

I wanted to keep the 2011 for parts, but it seems that the 2010 is different... Different logic board, LED screen connectors. The power supply looks the same and my extra bigger RAM chips work in the 2010.

I might end up having to sell the faulty 2011 for parts...

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Daniel Hebert will be eternally grateful.
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