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  1. #1
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    820-3588-A Chime reset chime reset (chime loop)

    Customer bought in aniMac 21.5

    Board 820-3588 a

    Out of the blue it does not start anymore

    When pressing the power button the iMac chimes every 2 seconds


    Thats all

    All Power supply measure OK
    No sign of water
    or other damage.

    Only thing i could see is that the LCD has been replaced.
    So it might have suffered a shock which broke the LCD in the past ...
    Last edited by Rene; 06-14-2018 at 05:11 AM.

  2. #2
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    Re: 820-3588-A Chime reset chime reset chime reset

    disconnect the power button, jump it to start and see if that still happens. I've seen a few wonky power buttons on those stupid things. (button plugs in on the PSU)

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    Rene (06-14-2018)

  4. #3
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    Re: 820-3588-A Chime reset chime reset chime reset

    now that you mention it.
    It looks like the power button has been replaced in this unit.


    But disconnecting the power button does nog solve the issue ..
    I will measure the power button signals on the logicboard

    I have the iMac on the workbench with the LCD disconnected
    3 Diagnostic LEDS light up. (4th does not since the lcd is disconnected)

    If the power supply was bad i think there would be a blink of these LEDs
    All 3 are steady ON


    I have exchanged the 2 RAM strips as well
    without RAM it beeps.
    Known good RAM has the same behaviour
    Last edited by Rene; 06-14-2018 at 03:03 AM.

  5. #4
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    Re: 820-3588-A Chime reset chime reset chime reset

    unless you have a spare PSU, it's worth scoping it and making sure it isn't dropping during the reset; it should stay a constant 12v. I sincerely doubt there's anything wrong with the PSU though. I'm guesing you've reset pram/smc? what does it do when you boot it in SMC bypass mode?

  6. #5
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    Re: 820-3588-A Chime reset chime reset chime reset

    Bypass mode on the iMac ?

  7. #6
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    Re: 820-3588-A Chime reset chime reset chime reset

    Measured some more

    U5210
    SPI_MB_MOSI = 0v
    SPI_MLB_CLK = 0v


    That does not seem ok

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    Re: 820-3588-A Chime reset chime reset chime reset

    unplug power, hold power button, plug in power, keep holding for a fw seconds, then release button. system will boot without using the SMC.

    anyhow, mosi is a data line and clk is a clock signal, so short of making sure they aren't shorted, a scope is the tool you want to be be measuring those lines with. more importantly, if either of those two weren't right, you wouldn't get a chime.

    anyhower, check your S5 power rails and see if any of them are dropping during the reset

  9. #8
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    Re: 820-3588-A Chime reset chime reset chime reset

    Bypass SMC gives the same results.

    All S5 powers are within range and stable.



    There are only 2 lines that are fluctuation.

    SNS_ACDC_N
    SNS_ADDC_P


    Both come from the power supply to the logicboard.
    Is this a temp sensor on the power supply ?

  10. #9
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    Re: 820-3588-A Chime reset chime reset chime reset

    at this point your best bet would be to go over the board under a microscope and look for any burnt/damaged/browned components for a clue. likewise, check ALL S0 rails, you might have one that's a little off. if all S0 rails are good, give me diode mode measurements and I'l compare to a known good I have here

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    Rene (06-18-2018)

  12. #10
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    Re: 820-3588-A Chime reset chime reset chime reset

    Thanks

    I will measure and make a list of the results.

    thinking out loud:
    Could it be "just" a corrupt bios/efi ?

 

 

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