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How can I test the Power Supply or Backlight Board (voltage values)? Power Supply 310 W (661-5972) (LiteOn) Backlight Board 661-5980 Model: iMac 27" - Mid 2011 - 3.1 Ghz AMD Radeon HD 6970 1Gb. Black screen, no power beep, fans spin, cd drive sound, no led keyboards. Board Leds Behavior: led 1: on led2: on led 3:off led 4:off
This sounds like a GPU issue which is well known on this model. To test, hook up an external monitor. Apple did do recall for these models but it has now expired: The problems have been documented over the past couple of years on Apple’s own Support Forums. Additionally, the iMacs must fall in the following serial number configurations: The last four characters of the serial number must contain one of the following groups (for example, xxxxxxxxDHJQ): DHJQ, DHJW, DL8Q, DNGH, DNJ9, or DMW8 DPM1, DPM2, DPNV, DNY0, DRVP, DY6F, F610 Here’s more info on it: https://9to5mac.com/2013/08/16/apple-ope… A hot air station reflow of the GPU card has been effective as a fix.
