PowerMac G4 MDD won't turn on after clean shutdown.

[Loganius]

I have a mid 2002 1.25GHz PowerMac G4 MDD which works perfectly, except for one thing. If I cleanly shut down the G4 in Mac OS, I can't turn it back on without physically cycling the power to it (as in, unplug it and plug it back in). It's had this issue since the day I got it (I bought it used about a year and a half ago). This doesn't occur if I force shutdown the computer by holding down the power button, however. I've tried resetting the PRAM and the PMU; neither helped. Any ideas as to what could be causing this, and how to fix it?
For what it's worth, it still has the original power supply, although I did swap the fans for some Noctuas. All the caps on the motherboard look fine (I checked them today), and if I remember correctly all the caps in the power supply looked fine when I was doing the swap, although it has been over a year since then.
Thanks for your time, and please be kind. This is my first time posting on 68kmla.

 

[croissantking]

I would recap the PSU as a matter of course. They are extremely unreliable in this model.

 

[Loganius]

I would recap the PSU as a matter of course. They are extremely unreliable in this model.

I've heard that (quite possibly from messages you've left in other threads lol). I'd rather not if I can help it since I have very little experience soldering, and am a little nervous to crack open the power supply (again). Besides, I don't even know what caps I would need.
Is there any way I can tell if the PSU is the issue before I go recap it? If not, can you give/link me a list of the caps I will need so I can at least come prepared? And also, do you have any advice to help me avoid, say, shocking myself or ripping off the pads? I really don't want to ruin my PowerMac .

 

[croissantking]

I can’t provide you with safety instructions sorry youre on your own

But I can share a mouser cart with the parts needed if you want

 

[Loganius]

But I can share a mouser cart with the parts needed if you want

That would be helpful, thanks.

 

[Byte Knight]

Welcome! I have the exact same issue with my MDD. It's only been a minor annoyance so I haven't bothered looking into it. Let us know if recapping the power supply fixes the issue.

 

[croissantking]

That would be helpful, thanks.

Sharing my Mouser cart here.

Diagram attached.

 

[mikes-macs]

Let us know if recapping the power supply fixes the issue.

My Dual 1.42 G4 had this same problem too. Eventually, it would not turn on at all no matter how many times I unplugged it. I paid a local TV repairman (yes they still exsist )to recap the power supply. Has been working correctly ever since then.
If you don't trust yourself to repair it then hire someone as I did. Try to have someone local do it if possible so you don't have to ship it off and pray that they don't disappear from the planet and keep it for themselves. Even if you do have to ship it and pay a lot for repairs it's better than destroying the Mac or burning down the house.