G4 and G3 PowerMac PSU's

[CooperBox]

Could someone please advise why the PSU's on many G4 and G3 PowerMacs are defective. I've been looking for a G3 b/w PowerMac for some time and most ads I've seen say: "does not boot probably due to defective PSU." 

Was the weak point on many G4/G3 PowerMacs the capacitors? If so have any of you sucessfully changed them out?

 

[Roman78]

Good question. I don't know if the Capacitors are the problem. On my G3 i suspected the mainboard to be faulty.

You can mod a normal ATX PSU to work in a G3 and G4, well at least in a G4. A modern PSU is also more effective and quieter. Problem in a G4 is that using a normal PSU won't generate the 24 or 28 Volts for the ADC monitor.

 

[weckart]

The PSUs on MDDs were notorious for their fragility. I would suppose this was due in some part to the cramped internals added to the additional power these PowerMacs pushed through, which may stretched the PSUs beyond endurance.

This seems to be less the case with previous PowerMacs. Rev A B/Ws had flaky Logic Boards that tended to complain if you tried to attach more than one hard drive.

 

[AL1630]

The PSUs on MDDs were notorious for their fragility.

Yeah, they're rare enough that MDD PSUs with new caps cost 2-3x more than Sawtooth or Quicksilver PSUs. Also, weren't the 360w Samsung units that replaced the 'Wind Tunnel' AcBels more likely to fail?

 

[weckart]

Yeah, they're rare enough that MDD PSUs with new caps cost 2-3x more than Sawtooth or Quicksilver PSUs. Also, weren't the 360w Samsung units that replaced the 'Wind Tunnel' AcBels more likely to fail?

I believe there was a particular capacitor on the Samsung units that was particularly wont to fail. Nothing too taxing for anyone handy with a soldering iron. The Acbel units were supposedly a little easier to work on if you needed to recap them.

 

[bunnspecial]

FWIW, the later you get into the G4 era, the more complicated an ATX swap becomes. It's still doable, but there are some specific requirements that you need to watch for to get reliable sleep/wake behavior.

Also, you lose ADC compatibility with an ATX PSU. Sawtooth and earlier G4s are easier for this reason alone.

There are pin-out diagrams online that show you what needs to be changed around on the PSU.

Beige G3s are the easiest since there's quite literally a jumper on the logic board that allows you to use an ATX PSU plug and play.

 

[CooperBox]

There's some valuable info here. Thanks to all for the feedback.

 

[bobesch]

Here's an adress of a workshop located somewhere in the 'Black Forest' (a region well known for their inventive people) to repair PowerMac PSUs ...
http://www.golytronic.de/reparaturen/g4-mdd/index.html

 

[Roman78]

Interesting. But you can mod an normal PSU into the MDD.You have to look for one whit a low profile circuit board, so one whit a big 120 or 140mm fan at the bottom.

It is a little bit tricky work, but it is possible. Somewhere i still have some photos of one I fixed some years ago.

 

[VanneDC]

Thanks, I have 2 pm g4's which will no doubt need this in the future. Any specific details on modding guide for the G4?