Is my PowerMac G4 MDD....DEAD?!

Discussion in 'PowerPC Macs' started by MrCheeto, Aug 29, 2009.

  1. macrumors 68030


    How can I tell what's wrong with this busted G4 I just bought? I assume it could be the easy to replace PSU, but I fear it could be the dreadful *gulp* FATHERBOARD!!!

    When I press the power button, I get NOTHING! No beeps, no whirs, I don't see a fan stutter and the LED doesn't do a thing. :D

    Also, how can I tell if it's dual or single CPU? It just says "1.25ghz" on the back label.
  2. macrumors 601


    The PSU is more than likely shot. Good luck replacing it for under $100 :p. You can still sell your "dead" psu for a few bucks as people out there refurbish them. You can take it apart to see if it's just the fuse that's blown.

    If it's a dual processor, it will say 1.25DP on the back label :p.

    Good luck and let us know how everything works out.
  3. macrumors 68030


  4. macrumors 68030


    Is there a way to test to see if it's the PSU besides getting a new one?
  5. macrumors 601


    You can manually jumper the PSU(I think it was the green wire and any black wire) to turn it on and then with a current tester, you can check all the pins for correct voltages. Also if you jump the 2 wires(check to be sure) it should also turn the fans on so if that doens't work, then more than likely it's shot. Also take apart the PSU to check the fuse if it won't turn on.

    Here's a link to the correct voltages,
  6. macrumors 68030


    ZOMG! I'ma gonna poop in my pants!

    First off, the beginning.

    5 months ago I bought 5 dells for $100. I cleaned them up, put XP on 'em and sold some. Some guy emailed me saying he needed help with his PMG4, I instead offered to trade a working Dell for his dead G4. He brought it over and we made a fair trade, I swapped the optical drives because he wanted to keep his DVD writer.

    Investment: $25

    So, I got to work diagnosing the problem. NO reaction to the power button being pressed, no fans, that means...the power supply! $100? :(

    But I got curious and cracked it open and saw a big tiny little huge fuse glaring at me! It was dark so I thought "BINGO! What a deal!" but turns out it was painted by the manufacturers that had placed it there, I dunno, to twist my leg or something. So then I went into a deep depression and even contemplated pesticide, but when I studied the fuse even closer...I realized...even though the center element was in tact one of the ENDS had blown!!!!

    OH HAPPY DAY! $27 and I haz a working PowerMac!! Well not yet, I'm buying a fuse today but I WILL keep you updated!! ^.^


    You can see a tiny bit of black paint on the right end, what kind of #$%& does that sort of thing?!
  7. macrumors 68030


    Crap! I bought a fuse, put it in, and it burned right through it as soon as I connected power!

    Come ON!

    So this means it's shorting out somewhere, most people will tell me to buy a new one but I'm telling you I'll fix it! Just tell me how to find the culprit >8\
  8. macrumors 601


    Lol. I had one of those problems with my MDD too. Took me 3 fuses before I realized it :D lol.

    Check solder traces on the PCB board of the PSU. I heard/read that the solder actually melts causing a short since they get too hot. I never could find out what was wrong with mine so I just sold them on ebay for parts/repair, I believe I got $75+ for them.
  9. macrumors 68030


    Crap, what are the odds of finding someone that would repair it/exchange it for a fair price?

    As with any capacitors there's risk of lethal shock, how do I discharge this thing?
  10. macrumors 601


    I believe you just let it sit for 24 hours unplugged.
  11. macrumors G4

  12. macrumors 68030



    I don't see ANY solder joints that look more melted than usual, lul, nor are any crossing.

    Well, might as well start calling places. What's this "phone book" you speak of?
  13. macrumors G4

    You don't know what a phone book is?
    Where are you located?

    Odd, but OK. It's usually a book (thickness varies by location) that contains published telephone numbers for both local businesses and residential customers. Sometimes the business and residential sections are split into different volumes, but none the less, there's usually such a book(s).

    Worst case, look it up online. It would serve the same purpose (same information, just online). Take a look at, if you're in the US.

    Hope this helps. :)
  14. macrumors 68030


    Hey folky polks!

    I've decided to check the capacitors, some seem dry. I'll post after checking/experimenting with them ^.^
  15. macrumors 68030


    Update: can I tell which are bad? If they wobble a little as I poke them does that mean something? I've got a multimeter, what can I do to help determine which parts need replacing?
  16. macrumors 6502a

  17. macrumors 68030


    Thanks buddy.

    I've seen this but sadly I will lose the ability to plug in a ADC Apple Display :( I need that 25v pin ><
  18. macrumors G4

    Is there any brown/green-brown substance on the board (leaked fluid)?

    Pics would help immensely.

    BTW, have you been able to locate an electronics repair shop in your area?
  19. macrumors 68030


    Well I've been looking for ANYONE that does board-level repairs. TV and guitar amp techs and the like. I'm trying every shop in the area.

    Let me know what you want pics of. No, visually the board is pristine, I took a volt meter to the caps and all of them shoot up in resistance as if new. However the 420v cap has a TINY bulge in the top and stops at about 320uf. However the problem is somewhere the board is SHORTING, which wouldn't be caused by a cap not holding power.

  20. macrumors G4


    Caps can fail as a dead short. :eek: Leakage and bulging are big clues there.

    A pic of the stuffed side of the caps (non soldered) might help (all if possible, but definitely the bulged part).

    BTW, have you been at it with a soldering iron (first pic, left side)?
    Looks like there's been some rework (appears as rosin flux residue at large "blobs" of solder on joints).
  21. macrumors 68030


    "Caps can fail as a dead short." Ok, but when I take my multimeter to all the caps I don't get a short reading, it says Open...?

    No I haven't touched it. I recently fixed another person's MDD and used their power supply to test my machine, works perfect. I opened their PSU and the bottom of the board appears completely similar, even the rosin on the leads was just as globby in that area. Both are the Samsung replacements =\

    Caps cluster


    Slightly bulged top
  22. macrumors G4

    OK, so you know for sure the system itself is fine, and it's just the PSU. That helps, as you know once the PSU is sorted, you won't have any nasty surpises. :D

    I went back up to the previous set of photos. On the second, I noticed something on the smallish daughter card. In the upper left, it appears there's some scorching on a surface mount resistor(?) next to a pair of through hole pins. Also, the line of surface mount components at the top right. I can't tell if that's just flux residue, or something else (due to over heating).

    At this point, if you have the skills to dissasemble and test out each component, this would allow you to discover any dead part/s. But you might want to test out the daughter board first. If possible, your friends PSU could serve as a guide to detect what's good or bad. :)

    Otherwise, find a shop that can, if at all possible. :(
  23. macrumors 68030


    WOW! Good eye!

    Sadly (this is sad...right?) the cap that appears blown works fine as I just tested with the multimeter :( I'm disappointed, I thought I was done searching.

    Nice catch, thanks everyone. I'll try and nab me an unsuspecting nerd or something.
  24. macrumors G4

    If you're attending a universtiy, make a friend in the electrical engineering dept. ;)

    BTW, the bulge on the cap in question isn't bad, as many do bulge a small amount in high heat situations. Given the age of the PSU, it would be a good idea to go ahead and replace all the capacitors on it, as they do go bad over time. By 10 years, you should go ahead and replace them if it's an item you wish to keep working. ;)

    Good luck. :)
  25. macrumors member

    If you need a power supply for an MDD, I can send you one for the cost of shipping.
    Saves me having to toss away a functioning PSU...

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