SMC Reset Questions (nMP)

Discussion in 'Mac Pro' started by Infrared, Mar 29, 2015.

  1. Infrared macrumors 68000


    Mar 28, 2007
    I have read Apple's SMC reset guide and I would like to clarify one or two points.

    In Apple's guide:

    "Unplug the computer's power cord."

    They don't specify which end. Is either ok? Or is it sufficient to turn off power at the power strip without unplugging anything? That is, is it the absence of AC power itself, rather than the power cord, that is the important thing?

    Also: are the timings given (15 seconds, then 5) absolutely critical? I am wondering if they are minimum times.

    At night power to the computer is switched off at the wall (our electricity sockets have on/off switches next to them - I am not sure whether that is typical in some other countries). When I power up the machine, more than 5 seconds has usually elapsed since the power at the wall was turned back on. Could this mean I have been resetting the SMC on a daily basis without knowing it?

    Finally, is there any way of interrogating the SMC to ask it when it was last reset? I mean, you carry out this procedure and there are no obvious signs that anything has happened. That's a bit unsatisfactory to me.

  2. chrfr macrumors 604

    Jul 11, 2009
    It doesn't matter- it's the same thing regardless of which you disconnect.
  3. Infrared thread starter macrumors 68000


    Mar 28, 2007
    It wouldn't be impossible to design a computer that senses when the power cord is attached to the machine even if the cord supplies no power. It was with that possibility in mind that I asked the question about which end.
  4. IowaLynn macrumors 65816


    Feb 22, 2015
    Unplugging alone, or turning off at the UPS or source does not reset the SMC. In fact if you don't hit the power button for 10 seconds while it is unplugged you are not even likely to reset the SMC

    My Mac Pro has been off the mains for months, been shutdown and the UPS turned off at night and not once has that reset the SMC.

    Apple has "modified" the instructions for an SMC Reset 4-5 times and I swear they have not tested it.

    Back in the G4 MDD days, we stumbled upon how to do a PMU reset by hitting power along with pulling all the RAM.

    Unplug keyboard mouse and anything else though. Can do an NVRAM reset also from cold start to be thorough.
  5. Infrared thread starter macrumors 68000


    Mar 28, 2007
    SMC Reset Questions (nMP)

    That's interesting. I have seen that recommended for some Macs, but not in Apple's current instructions for the Mac Pro:

    1. Shut down the computer.
    2. Unplug the computer's power cord.
    3. Wait fifteen seconds.
    4. Attach the computer's power cord.
    5. Wait five seconds, then press the power button to turn on the computer.

    How can you tell when it has been reset?

  6. IowaLynn macrumors 65816


    Feb 22, 2015
    If like me, take some of what Apple says with a grain of salt, sometimes more :apple: They should maintain ALL the old tech articles in a footnote perhaps?

    The reset is not done except when needed to resolve or troubleshoot a hardware issue, a device not showing up, powermanagement issue. Optical drive not showing in the system profile etc.

    You will have to reset the default startup disk if you do NVRAM or SMC Reset.

    The answer was in the article you linked and goes on from there. And is often linked to from other troubleshooting articles.

    Note: It is possible that the SMC could encounter an issue that may cause unusual system behavior typically related to the symptoms described below. In some cases, resetting the SMC may be the only correct method to resolve the issue. However, an SMC reset should only be attempted after all other standard troubleshooting has been performed.
  7. Infrared thread starter macrumors 68000


    Mar 28, 2007
    When power was cut to the machine I tried pressing the machine's power button. There was a brief flash of light from one of the indicators. I don't know if that means anything.

    The more I think about it, the more bizarre it seems that this SMC reset procedure is recommended but there is no obvious way of knowing it has been successfully completed. I hope the procedure isn't just a sugar pill equivalent ;)
  8. h9826790 macrumors G4


    Apr 3, 2014
    Hong Kong
    When there is really something wrong (e.g. fan go crazy), then you will know if the SMC reset successfully or not.
  9. IowaLynn macrumors 65816


    Feb 22, 2015
    The Mac Pro began with like most motherboards with a reset button on the logicboard back in Intel labs in June 2005 as the Skulltrail. Apple I guess wanted to find a way around using a reset button.

    Whether G4 or G5 with PMU and SMU there has always been a mechanism and need, in part to fully reset the board but also to force scan of hardware to build a list of devices.

    I don't know if Apple's EFI has a dual EFI "BIOS" backup mechanism but most of my PCs do have something like that.

    When a G5 would not recognize you changed the SATA drive in bay A, when an optical drive would not show, when a PCIe card was changed (in the case of OpenFirmware that was a time when NVRAM or PMU needded to be cleared (ie, reset) and a new device tree list generated.

    A G4 MDD that would not boot and was "dead in the water" was perfect and it did happen often enough - not to same system but out of all the systems out there - that there became a common wisdom or urban lore of how to bring it back: To do PMU but with RAM removed and hitting power on button.

    And that is where my own understanding - and issues with IBM implementation of OpenFirmware on the G5 - has its roots. Just adapted to new systems.

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