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Thread: dead iMac 2010/27", contradictory diagnostic led and logic board test point voltages

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    Jul 2019
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    Default dead iMac 2010/27", contradictory diagnostic led and logic board test point voltages

    I have an iMac 2010/27" that died out of the blue. It was working fine, then later the same day was dead. No noise, no signs of life. I followed the diagnostic procedure found in the technicians guide

    I found:

    - no diagnostic leds are lit, not even diagnostic led 1
    - logic board test point 4 shows the expected 12 volt standby power
    - logic board test point 12 shows the expected power on request when the power button is pressed (the test point voltage is pulled down when the power button is pressed)
    - logic board test point 11 shows the expected 12 volt run-mode mode power after the power button is pressed

    The lack of any diagnostic led, not even led 1, indicates a bad power supply. But the presence of good logic board test point voltages indicates a good power supply. This is contradictory, hence I'm unsure how to proceed. Does anyone have any experience with this situation?
    Last edited by ricks; 07-07-2019 at 09:13 AM. Reason: removed link

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