MDD power issues

Discussion in 'PowerPC Macs' started by desantii, Apr 11, 2015.

  1. desantii macrumors 6502


    Sep 9, 2006
    Aurora, IL
    I am having some issues with my MDD.. Powers on fine for the first time then when powered off while not turn on again until it's unplugged and plugged back in... Any ideas
  2. Hrududu macrumors 68020


    Jul 25, 2008
    Central US
    Failing power supply. These things have the worst PSU's in Macintosh history. I'm 2 out of 2 for MDD G4s with bad power supplies. The good news is you can buy them on ebay, the bad news is they're more expensive than the computer is worth. If I were you I'd just ride it out and use it as is.
  3. robertdsc macrumors regular


    Jan 28, 2014
    I had two DP 1.0s go out on me with the same issue. I wound up junking them after taking the drive cages and IDE cables out.
  4. Orizence macrumors 6502

    Nov 10, 2014
    Have you considered converting a ATX power supply for your MDD, it would make a good project :p
  5. Czo macrumors 6502

    Dec 30, 2008
    Debrecen, Hungary
  6. for this, Apr 12, 2015
    Last edited: Apr 12, 2015

    for this macrumors regular

    Nov 18, 2014
    Almost all the cases like this are caused by bad catalytic capacitors in the PSU.

    I've found people share how they fix their PSUs in details here. Quite a few of them are MDDs.

    The replacement cap have to have matching capacity, similar size and ESR, and comparable or better ripple, voltage, and temperature ratings to the one it replaces.

    Usually the failing caps in an MDD's PSU are from Taiwan/China.
    You can selectively replace them and skip the Japanese ones. Japan make best caps. But I just recapped all the 26 catalytic capacitors in my MDD's PSU anyway (except the biggest three—they rarely go bad, especially if they're Japanese brands). It has been working like new now.
  7. poiihy macrumors 68020


    Aug 22, 2014
    I would make my own power supply :D

    I think all you really need is 12v, 5v, 3.3v, maybe -12v, and a relay or something to turn it on and off... But I don't really know anything about this...
  8. bunnspecial macrumors 603


    May 3, 2014
    I'm as much of a DIY guy as anyone else, but building a quality computer power supply isn't exactly just a matter of throwing a few parts together. You need to first step the power down with a transformer, then use a rectifier combined with a capacitor and probably an inductor to smooth it out(BTW, if your transformer steps down to an RMS AC voltage of 12V, you will get ~17V DC out of it when you do all this).

    As far as I know, most modern computer PSUs are high frequency switching PSUs, which has quite a few advantages in that the transformer can be much smaller and it's easier to get a smooth DC voltage out of it.

    If you want to tinker with one of these, your best bet is probably to use an ATX PSU.
  9. poiihy macrumors 68020


    Aug 22, 2014
    Well i was thinking of getting a few pre-made power supplies; a 3.3v, 5v, and 12v, and put them together, but I don't know if the virtual voltages (like connecting 12v to 5v gives you 7v) would work. :confused:

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