My MDD G4 won't switch on :-(

[Giuanniello]

I wanted to resurrect my old dual G4 MDD to use a same old scanner in need of a SCSI board which I had installed in the MDD, unfortunately by pressing the switch button I only get a blink off the in button white led and that's it, dunno if power supply is gone or if there is any fuse or other part to inspect, maybe the backup battery but I don't think it will avoid the power on procedure...

Any hint at what to check and, eventually, in case of a failed PSU, how to retrieve one or fix it?

Grazie

 

[Wild Hare]

Check this first…

http://www.jcsenterprises.com/Japamacs_Page/Blog/D275729F-09DA-4FBB-96B3-BEEEB2C04619.html

And yes, there’s a fuse inside the PSU (AcBel & Samsung models) but by the time you remove the PSU to get at that fuse, you might as well replace the capacitors (if it’s an AcBel, the Samsungs are a bit too tightly packed). And it requires some soldering skills.

Here’s an interior look at an 360W AcBel and some of the process involved…

http://macos9lives.com/smforum/index.php/topic,4088.msg28011.html#msg28011

*You might have to become a member, but it doesn’t cost anything & then you can then see the pics.

Chances are that a 20+ year old MDD has leaking or leaked capacitors and needs refurbished. Andy Cuffe in Austin, Texas (USA) does a fine job. (Info on Andy & contact info, also in that above thread.) But you can find some used… and still working - but they’re destined to fail as well, especially after all this time. Good luck!

 

[ervus]

+1 on the capacitors. I have repaired 3 of them. If the fuse were blown, you wouldn't get the light at all. You can use a modified ATX power supply, but they don't fit the case well.

 

[micahgartman]

WOW—you young bucks are jumping the gun on this.

If the MDD has been unplugged for a while, press the CUDA button on the logic board.

Here's where it's located:

 

[ervus]

I think you would want to confirm good battery voltage before trying that. I think the procedure is to do this with the computer unplugged, press the PMU reset switch only ONCE, then wait 10s, and connect power.

You could also try leaving the computer unplugged for a while, then plug in the computer and immediately press the power button. I've seen MDD computers with bad caps turn on with this method.

 

[z970]

For whatever it's worth, I was receiving the same behavior with my Quicksilver until I reset the PMU as @micahgartman now suggests. Once I did, it fired right up, good as new.

As I recall, I also believe my iMac G4 kept giving me the same behavior as well, sans power light. All that took was one PMU reset (each time it happened), and all was well again.

Needless to say, I think you should definitely first try that out before moving onto the PSU.

 

[Wild Hare]

Yes, most definitely try the CUDA /PMU reset first.
Mea culpa.

[Hard fought QS battle day (and night) here yesterday.]

I do appreciate the “young buck” reference.?

 

[Giuanniello]

Good day everybody, I opened the PowerMac door and hit the button but behaviour remained the same, till I keep the switch button pressed I get the white led to lit up but computer won't start, am afraid it might be the power supply in whose case I won't bother fixing it but wondering what's the exact procedure to reset the PMU on the PowerMac, press and hold for a certain amount of time...? Gonna give it another try when I go back there, thank you everybody in the meantime

 

[Wild Hare]

Here’s a very good source for the information that you seek (among other useful items as well).
*Scroll down to the CUDA/PMU section.

Google Sites: Sign-in

Access Google Sites with a personal Google account or Google Workspace account (for business use).

sites.google.com

 

[micahgartman]

Google Sites: Sign-in

Access Google Sites with a personal Google account or Google Workspace account (for business use).

sites.google.com

Fantastic resource. Thank you for sharing!!!