Reset PMU on old Imac?

Discussion in 'Mac Basics and Help' started by btcomm, Feb 16, 2007.

  1. btcomm macrumors regular

    Oct 18, 2006
    This imac is so old that it doesn't have a pannel that you can get into, that I can see anyway.

    It has what looks like 2 reset buttons on the right side where all the ports are.

    It has one that is a triangle and one that has a circle with a v in it. Do pushing either of these reset the PMU? How long would I have to hold them? If they don't reset the PMU then how would I reset it on one of these oldies?

    If it is one of those, how long would I need to hold the button?
  2. Makosuke macrumors 603

    Aug 15, 2001
    The Cool Part of CA, USA
    Those two buttons on the side are reset and the "programmer's button", neither of which do what you want.

    I can't remember the internal layout of those clearly (and it depends if it's a slot loading or tray loading model), but I believe to do the reset you're trying to the only way is to either crack it open and find the "CUDA" button on the motherboard (again, I forget if there even IS one on those, though), or to unplug it, remove the internal battery, push and hold the power button for five seconds, let it sit for an hour or two unplugged, put the battery back in, plug it back in, then boot it up and hope for the best.

    Easier said than done, since the batteries aren't easy to get to (I *think* you can get to the battery in the slot loading models through the RAM door in the bottom if you're careful, but you need to dismantle the tray loaders to get to anything).

    What are you trying to do this for? Is the thing refusing to start up after a power problem, or suddenly stopped working? If so, you might try just replacing the internal battery--when those die it can cause all sorts of annoying issues.
  3. btcomm thread starter macrumors regular

    Oct 18, 2006
    Well, the computer will power on for about 3 seconds, then it shuts it self off. After that you have to unplug it and leave it unplugged for a while before it will even turn on at all again. Otherwise, you push the power button and nothing happens.

    I don't even think there is a ram door on this old Imac, I know that the PMU reset button is accessable there on some of the slot loading old Imacs but this must be one of the very first ones. I don't see a way to get inside unless you unscrew it and take the whole plastic peice off the bottom.
  4. Makosuke macrumors 603

    Aug 15, 2001
    The Cool Part of CA, USA
    Since it's one of the original tray loading, you're correct--the only way in is to unscrew the back and pull the guts out (the motherboard as well as all the drives slide out in one big chunk once you disconnect everything).

    And if that's the symptom, it could well just be a bum power supply or something in the monitor shorting out and killing it, but getting in and replacing the battery might resurrect it. Too bad it's such a hassle with those--I've opened them up for upgrades more times than I care to remember, but I've skinned plenty of knuckles in the process.
  5. mlunacat macrumors newbie

    Mar 14, 2007
    PMU reset on slot loading iMac DV+ (Summer 2000 model)

    Knowledgable friends, any or all that may be able to advise:

    I have an iMac DV+ G3 Indigo 400 mHz that has worked well running OS 9.2.2 /10.3.9 since I bought it new back in March 2001 (except for an oddity with the gradually-getting-blurry built-in display that has caused me to use an external monitor with it for the last two years). This iMac has been unable to power up as of 15 days ago.

    I came home on that day to my clock blinking and my VCR needing a reset, so obviously we'd had an off-on again power problem hours earlier. All my electronic components - including this one - are plugged into good suppressors, and this was the only electronic device in my entire apt to be badly affected by this power failure/surge; my older 8100, the 19" monitor, laptop, DSL modem, router, and powered USB hub were all fine (and nothing like this has never happened before in the 8 years we've been in this apt).

    To try and determine the source of the failure, I checked/ tested the USB, all cables, the suppressor, the outlet -- all fine. So I can say it is the computer.

    It was recommended that I first try to reset the PMU on the logic board, and try to power up again, as that has resloved other situations like this before, then if that doesnt work, see if resetting the battery (as is suggested in a post above in this thread) then resetting the PMU again, just once more, works. After these tests, I have been advised that if it still doesn't power up, it is likely to be a deeper issue that I would not be wise to try and repair myself.
    I would also be fine with replacing the battery, as I have found a website that has them :

    highly recommended for anyone with an older imac -- ''

    Problem is, I am having a very hard time finding the actual PMU reset button on the logic board. I do actually have access to that area, at a sideways-downward angle, thru the RAM access door, and can also get close enough to read the incredibly tiny letters and numbers next to each little thing on the logic board.

    I found an amazing website that had all the Mac tech service manuals, and on page 196 of the pdf-manual (imac_DV.pdf) - I found a surprisingly indistinct picto-diagram of what the PMU reset button is supposed to look like -and- it does not provide an alphanumeric character corresponding to certain points on the logic board (as it does in other parts of this manual, when testing for 'trickle power', for example); It just points vaguely to a little dot on the board, while the text on page 197 says: "refer to diagram for location of button". (argh!!)

    I truly cannot tell what I am supposed to push. Would anyone know the corresponding AN character on the board next to that specific button?

    Also, how would you recommend getting the battery in and out, via that tRAM access door, if you have any suggestiions?

    any and all help truly appreciated

  6. spork183 macrumors 6502a


    Jul 30, 2006
    You should probably take this and start a new thread, since answers to your question here will not assist the original poster who has a different model imac, with different access issues. :)
  7. mlunacat macrumors newbie

    Mar 14, 2007
    Thanks-- will do --
    I wasnt sure which was the more appropriate thing to do ("newbie" to forums, as i am)

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