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vitorio
Feb 9, 2010, 01:18 AM
hi everyone, i've been reading the forums for some time (mostly around apple update time), but now the time has come to participate

Recently i got an old powermac G4 from a friend. He got it from his company, because it was dead. It is a MDD model, with dual 1.25GHz cpu's and a radeon 9000. Ram and HDD were missing, but i have spares for that.

Now i plugged in the power, and it didnt do anything, nothing at all. So i opened it up, and turns out the PSU is fried (fuse blown, apperently G4 PSU's die a lot). So i spent last night adapting a normal ATX psu to the G4's wiring harness. (leaving the 25v alone, which apparently is only needed for the ADC).

Now it still doesnt start up, when i push the power button really hard, it lights up sometimes, untill i take my finger off, then it fades away, and thats all it does. I tried the PMU reset in several ways (with battery, without battery etc..), and still, nothing.

Does anyone have a good idea of how to fix this? I would love to get this machine up and running, since it would be a nice machine to discover OS X on (leopard anyway), but if it is dead, then so be it..



dbculp
Feb 9, 2010, 06:16 AM
When I put an ATX PSU into a Digital Audio G4 I ran +12V to the +28V pin and that was enough to allow the machine to boot. Double check your wiring, the MDD layout is kind of odd and very different from anything else.
The problem might just be the front panel button, apparently they are known to go bad.

vitorio
Feb 9, 2010, 06:38 AM
When I put an ATX PSU into a Digital Audio G4 I ran +12V to the +28V pin and that was enough to allow the machine to boot. Double check your wiring, the MDD layout is kind of odd and very different from anything else.
The problem might just be the front panel button, apparently they are known to go bad.

hmm i see, i'll hook the 25v to the 12v rail and try that

as for wiring layout, i just cut the 24pin connector from the mac PSU and tied the wires into and ATX female plug, grouping them by color (color/voltage is the same in ATX/Mac)

I assume i can fake a power up by shorting two mobo pins in under the front panel connector? any idea which two pins to short?

AlexMaximus
Feb 9, 2010, 11:17 AM
hi everyone, i've been reading the forums for some time (mostly around apple update time), but now the time has come to participate

Recently i got an old powermac G4 from a friend. He got it from his company, because it was dead. It is a MDD model, with dual 1.25GHz cpu's and a radeon 9000. Ram and HDD were missing, but i have spares for that.

Now i plugged in the power, and it didnt do anything, nothing at all. So i opened it up, and turns out the PSU is fried (fuse blown, apperently G4 PSU's die a lot). So i spent last night adapting a normal ATX psu to the G4's wiring harness. (leaving the 25v alone, which apparently is only needed for the ADC).

Now it still doesnt start up, when i push the power button really hard, it lights up sometimes, untill i take my finger off, then it fades away, and thats all it does. I tried the PMU reset in several ways (with battery, without battery etc..), and still, nothing.

Does anyone have a good idea of how to fix this? I would love to get this machine up and running, since it would be a nice machine to discover OS X on (leopard anyway), but if it is dead, then so be it..


Hey there,

attached are some infos that helped me a lot with my past G4 project.

G4MDD - ATX conversion:

http://www.applefritter.com/node/23857

and this :

http://www.smartfruit.com/node/58

.. as well as this:

http://www.youtube.com/watch?v=xICg592xJTg


You should be able to find out what you have missed, once you have read/watched the articles mentioned above.

Good luck to your G4 project!

:apple:

vitorio
Feb 9, 2010, 12:38 PM
well, i modified my wiring slightly:

- ran 12v to the 25v rail on the mac connector
- isolated the 3.3v sense wire from the rest of the 3.3v rail

sadly to no effect, then i ran my screwdriver across the front panel connector to try and jumpstart it in case the powerbutton was wonky, yet no luck

all that happens with this thing is that the power button lights up when i push it really hard, nothing else what so ever :(

anyone else have a brilliant idea on how to fix this thing? or is it just a dead mobo?

OrangeSVTguy
Feb 9, 2010, 03:23 PM
Make sure the processor daughter card is fully seated. If it's dead or not connected, the G4 won't even turn on.

dbculp
Feb 10, 2010, 10:18 AM
This may sound a little odd but try pushing the power button until it momentarily lights up, unplug the computer for 10 seconds, plug it in and immediately push the power button again.
You can also try bypassing the front power switch by putting a jumper from the green startup wires to the grounds next to them.

vitorio
Feb 10, 2010, 01:23 PM
Make sure the processor daughter card is fully seated. If it's dead or not connected, the G4 won't even turn on.

well, i reseated the cpu card, and redid the thermal paste while i had the heatsink off, no effect

This may sound a little odd but try pushing the power button until it momentarily lights up, unplug the computer for 10 seconds, plug it in and immediately push the power button again.
You can also try bypassing the front power switch by putting a jumper from the green startup wires to the grounds next to them.

i tried the 10 second trick, didnt work. I tried jump starting the psu, which works, if i try jumpstarting it with the mac attached, nothing happens (psu doesnt power up), although the fans gives a tiny little twitch, as though the psu wants to spool up for a fraction of a second, but the system cuts out the startup...

so the thing still is dead as a doorpost

any more suggestions, or should i just throw the thing in the trash?

arogge
Feb 28, 2010, 04:26 PM
I have this same problem with the same computer version. I had the computer powered off because of power outages, and when I pushed the power button, nothing happened. When I push it hard and hold it down, the light turns on but fades off as soon as I let go. What I did notice is that the fans have been making unusual noises over the past few weeks, sometimes there would be no video signal after Wake from Sleep, and my new DVD drive was suddenly not spinning up DVDs or was failing to finish writing them. Maybe Apple killed our computers as part of some sort of forced upgrade plan.

Maybe this could mean that new product releases are coming this week! It's a sign that's it's time to upgrade. :D