iMac G4 - 160 or 180 Watt PSU?

Discussion in 'PowerPC Macs' started by AL1630, Mar 27, 2018.

  1. AL1630, Mar 27, 2018
    Last edited: Mar 27, 2018

    AL1630 macrumors 6502

    AL1630

    Joined:
    Apr 24, 2016
    Location:
    Idaho, USA
    #1
    I just picked up a 17 inch iMac G4 cheap on Craigslist, model number M6498. It doesn't work, and from what I've been seeing, the problem is most likely to be the Power Supply. When the power button is pushed, nothing happens at all, not even the fan spins up. Is this the power supply or could it be something else? I've also been looking at eBay for new PSUs, and there are 160 and 180 Watt models. Which one is the correct one for this model, if that's problem?

    Edit: I looked up the Serial Number, and it's the 2004 USB 2.0/1.25 Ghz Model
     
  2. DeltaMac macrumors G3

    DeltaMac

    Joined:
    Jul 30, 2003
    Location:
    Delaware
    #2
    Appears to be 160 watt. The 15 and 17-inch share the same power supply in the USB 2.0 models. The 20-inch uses a different PS, and likely with the larger screen would need more power from the PS.

    Anyway, the Apple part number for the correct PS for your 17-inch, USB 2.0 is 922-5796 .
    That would probably be the best plan to search with that part number.
    There are multiple sources that can provide that power supply.

    But, did you try to reset the PMU? This might resolve the power problem.
    1. Disconnect the power cord.

    2. Remove the user access panel from the bottom of the computer.

    3. Press the PMU reset switch (located under the protective cover, next to the test points) once on the bottom side of the logic board and then continue. Do NOT press the PMU reset switch a second time because it could crash the PMU chip.
      Wait ten seconds before connecting the power cord and powering the computer.
      If your iMac still does nothing, the Service manual says logic board might be more likely failure than power supply.

    But before the PMU reset, be sure to check the battery. IIRC a dead battery can cause a no power condition on those iMac G4s.
    1. Locate the battery test point.

    2. With the computer powered off, measure the battery voltage. Does the battery measure at least +3.5v? If no, replace the battery and reset the PMU. If the battery measures +3.5v or higher, reset the PMU as above.
     
  3. AL1630 thread starter macrumors 6502

    AL1630

    Joined:
    Apr 24, 2016
    Location:
    Idaho, USA
    #3
    I tested the battery, and it checked out. PMU reset also didn't do anything. It there a way to test if it's the PSU or board?
     
  4. DeltaMac macrumors G3

    DeltaMac

    Joined:
    Jul 30, 2003
    Location:
    Delaware
    #4
    Sure,
    Check for 12 volts on 5 separate pins on the power supply connector. You have to open the bottom housing to get access to the power supply.
    No voltage, replace the PS.
    If you have voltage, replace the logic board.
     
  5. AL1630 thread starter macrumors 6502

    AL1630

    Joined:
    Apr 24, 2016
    Location:
    Idaho, USA
    #5
    OK, I'll be taking it apart when I've got some time. Thanks!
     
  6. AL1630, Mar 30, 2018
    Last edited: Mar 30, 2018

    AL1630 thread starter macrumors 6502

    AL1630

    Joined:
    Apr 24, 2016
    Location:
    Idaho, USA
    #6
    All right, I just took off the bottom and tested the power supply, and it measures around 12 volts at the connectors specified in the Service Source, so I guess the logic board is bad. Anything else to try before I try to find a new one?

    Edit: Is the 1GHz Logic Board compatible with the 1.25 Chassis? the 1GHz model is significantly cheaper than the 1.25.
     
  7. DeltaMac macrumors G3

    DeltaMac

    Joined:
    Jul 30, 2003
    Location:
    Delaware
    #7
    The video on the 1Ghz USB 2.0 board would be a downgrade for your 17-inch display, but should work.
     
  8. Project Alice macrumors 6502

    Project Alice

    Joined:
    Jul 13, 2008
    Location:
    Post Falls, ID
    #8
    I have the 1Ghz model. It is USB 1.1, there is no USB 2.0 model of the 1Ghz. If i were you I'd buy the one you have, which was the fastest one available. The graphics on the 1Ghz model does not support core image so makes leopard run like crap. Im probably going to downgrade mine to tiger or at least dual boot because of this.
     
  9. DeltaMac macrumors G3

    DeltaMac

    Joined:
    Jul 30, 2003
    Location:
    Delaware
    #9
    That is inaccurate information.
    The 15-inch iMac G4 USB 2.0 is 1GHz.
    1GHz was offered in the 17-inch before the USB 2.0 models were released, and the 15-inch USB 2.0 had a 1GHz processor. As I said, it should go right in, as the case and connections are the same. But, the video chip has only 32MB of VRAM, compared to the 64MB VRAM in the 17-inch. Other than the display (and the logic board), the two are identical.

    (the video chip may not support Leopard very neatly, but the system bus IS still faster, and Leopard may be "OK" )
     
  10. Project Alice macrumors 6502

    Project Alice

    Joined:
    Jul 13, 2008
    Location:
    Post Falls, ID
    #10
    Yes, I was referring to the 17" 1Ghz model. which is only USB 1.1. He didn't exactly specific which 1ghz board he was looking at buying. I assumed the 17" one. Either way, both 1Ghz machines come with a GeForce4. The 15" one apparently has even less vram then mine. I'm only recommending that he get the 1.25 because He'll be much happier.
     

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