13 Replies Latest reply: Mar 10, 2008 5:49 PM by Brett Rockwood
Brett Rockwood Level 1 (5 points)
I feel really silly asking this but here goes anyway. I have a PowerMac G4 dual 1.25Ghz MDD FW 800 and an Apple Display Studio display. I use the power switch on the front of the display to turn the system on. No problem there. I want to sell the CPU but keep the Studio Display. I have a Sony display that doesn't have the integrated power switch that i would like to sell with the CPU. But when I disconnect the Apple Studio display I can't turn the CPU on. When I press the power switch on the CPU, nothing happens.

I can power on using the Studio Display and have even swapped out the monitors while the machine was running and the video works fine on the Sony display. But when I shut down i can't restart without reconnecting the Studio Display and using its power switch.

Surely I'm missing something really stupid... Any suggestions?

Dual 1.25 G4 MDD 800FW, Mac OS X (10.4.11)
  • Douggo Level 4 (2,740 points)
    Connect the Studio Display, start up then go to System Preferences->Displays->Options and unmark anything set there for controlling the G4. Restart doing a PRAM reset (Command-Option-P-R keys held at boot until you hear the startup chord twice and release) then shutdown and swap displays. See if your front panel power button works then.

    -Douggo
  • Brett Rockwood Level 1 (5 points)
    Thanks for the quick reply. I checked the display settings and nothing is selected. Only 2 choices, 1 is "disable to power button" on the display and the other is to "disable display preferences button" on the display. I'm afraid to disable the power button on the display as it's the only way I currently can start up...
    I did zap the PRAM but still no response from the power button on the CPU. Any other ideas?
  • Brett Rockwood Level 1 (5 points)
    So I tried disabling the power button on the studio display and as expected I now can't turn on the CPU at all... I have another PowerMac here and have re-enabled the power button on the display so hopefully I'll be able to reboot it again.
  • Hans777 Level 2 (445 points)
    Brett,
    there is a discussion going on about this problem you might want to view.
    http://discussions.apple.com/thread.jspa?threadID=1360134


    Hans
  • Brett Rockwood Level 1 (5 points)
    Hans,
    Thanks for jumping in. Your info was very informative. The battery was one of the first things I suspected. When I checked it on a voltage meter I thought it was OK but it definitely wasn't at full voltage. Maybe it needs to be spot on to work. I'll try replacing the battery and see what happens.
  • Hans777 Level 2 (445 points)
    OK, be sure to report back.

    Hans
  • Brett Rockwood Level 1 (5 points)
    Hans,

    I picked up a new battery today and installed it but no luck... Still nothing happens at all when I touch the power switch. It's an odd switch, it doesn't really move or click or anything. I assume it just senses the capacitance change when your finger touches it, like my old G4 Cube.

    I wonder if you have any other suggestions... I can hardly sell (or even use) a CPU that can only be powered on by an Apple Studio Display.

    Thanks again for your help.

    Brett
  • Hans777 Level 2 (445 points)
    Brett,
    did you reset the PMU? You do that by pressing the tiny button next to the battery ONCE FOR FIVE SECONDS.
    If the PMU reset has no effect you either have a power supply problem or a bad front panel board. That big lit plastic button operates a tiny microswitch behind. The latter is soldered to a small PC board with additional components on it. Two wires (or 3?) lead to a socket close to the big power supply connector on the motherboard.

    Hans
  • Brett Rockwood Level 1 (5 points)
    Hans,
    Thanks again. I just reset the PMU but still nothing. Doesn't sound good.
    I can see a ribbon cable coming out of a housing that looks like it contains the power switch but I can't really see where it ends up. Should I just be making sure it is connected somewhere?
  • Hans777 Level 2 (445 points)
    The front panel board is behind a metal cover which you can remove to get access to the board. You can make sure that the cable is safely connected on both ends but chances are that you won't find any flaw. To go on with troubleshooting could you rate your own skills with electronics and VOMs?

    Hans
  • Hans777 Level 2 (445 points)
    In case you feel confident to do this:
    Remove the power chord.
    Pull all external connectors including ADC cable.
    Put the Mac on your desk. The side panel stays open during the process.
    Pull power connectors from all internal hard drives.
    locate a green wire in the PSU power connector and a adjacent black one - all blacks are ground. Push a paperclip bent in U-form deeply into the holes where the wires enter the connector.
    You can also push one needle pin through the centers of both wires.
    Connect the power chord to the wall outlet and listen for chime. Observe the red LED on the motherboard - does it stay on?
    If so your PSU is likely OK and the front panel board is bad.
    If there is no chime and no LED lit the PSU is at fault.
    Remove power chord to reassemble the system and remove the clip/needle.

    I might not be able to answer the next two days.
    Good luck.

    Hans
  • eighth-1der Level 1 (75 points)
    I have the same computer.
    Mine takes 2-3 seconds of solid touch (not really a push) to turn on and if I KP or freeze, the same 2-3 up to 5 seconds to turn off.

    Try the solid touch. The button does move, but less than 1/16 inch.

    The old "legacy" Macs had power buttons on the keyboards that would take several seconds. There was something about power saving by less frequently sampling the keyboard during "power down". I have several USB keyboards with power keys that only turn OFF the USB Macs.
  • Brett Rockwood Level 1 (5 points)
    Thanks for jumping in. I know what you mean about holding it for a few seconds. I've had to do that on rare occasion of a kernel panic. I have been holding it down for a number of seconds as you suggest; and it does move about 1/16 of an inch but still no action or lights.

    I don't have one of the old keyboards with power buttons, but it's interesting that they only turn it OFF and not ON. Thanks for letting me know that as I was thinking of trying to find one and giving it a try.