68kMLA Classic Interface
This is a version of the 68kMLA forums for viewing on your favorite old mac. Visitors on modern platforms may prefer the main site.
| Click here to select a new forum. | | PowerMac G3 AIO PSU Recapping Help | Posted by: cgober on 2026-08-26 11:13:49
Hi all, first post. Diagnosing a Power Mac G3 All-in-One that was brought to me that won't turn on, and I've isolated the fault to the power supply. When you try to start the machine the PSU seems to fold back on itself when trying to bring up the main rails.
Standby (5V) is solid - steady ~4.9V.
Main rails fold back / hiccup: on power-on, 5V / 3.3V / 12V all rise partway then collapse together, with a fan-twitch and an audible buzz.
I was able to get it to chime for me by hooking up an ATX power supply, so I think the logic board is good. I've yet to connect it to an external monitor as I lack the proper adapters, but when I get them I'll be checking that as well.
Visually, the power supply doesn't look bad at all, but I know that these problems don't always have a visual component to them... Looking for someone who can recap the PSU for me or potentially further aid in it's restoration.
Any help would be greatly appreciated - Thanks! | Posted by: Durosity on 2026-08-29 12:33:09
So I spent a little time with these a couple of years ago, but PSUs aren’t my area of expertise so do be careful! One thing I’d suggest is detach the ribbon from the personality card on the motherboard and see if the Mac starts up that way. I have a faulty AIO which will start up with it detached, but if it’s connected it’ll cause it to trip. That’s helped me narrow down where the fault area is, however I’ve not since spent the time looking into it further.
Also it could be an issue with the analogue board/neck board. | Posted by: cgober on 2026-09-03 11:08:48
So I spent a little time with these a couple of years ago, but PSUs aren’t my area of expertise so do be careful! One thing I’d suggest is detach the ribbon from the personality card on the motherboard and see if the Mac starts up that way. I have a faulty AIO which will start up with it detached, but if it’s connected it’ll cause it to trip. That’s helped me narrow down where the fault area is, however I’ve not since spent the time looking into it further.
Also it could be an issue with the analogue board/neck board. Thanks for the reply. I think I found someone I can send the part to. I removed essentially everything and tried to run the PSU that way and it you can hear a faint clicking sound - rails come up briefly then the voltage falls off. Hopefully the fellow I sent it to can restore it 🙂 | Posted by: Durosity on 2026-09-03 11:46:32
Thanks for the reply. I think I found someone I can send the part to. I removed essentially everything and tried to run the PSU that way and it you can hear a faint clicking sound - rails come up briefly then the voltage falls off. Hopefully the fellow I sent it to can restore it 🙂 Fingers crossed! If they can please let me know who it was, might help with mine 😅 | | 1 |
|