G4 MDD SfX PSU

[jovianartifact]

sup nerds, I'm about to replace the PSU in my MDD with a new SFX one.
I picked the SFX because it looks like they're a perfect fit for the insides of the case, and I'm stoked about the idea of having double the nominal power output AND proper SATA plugs so I can stacc this bad boy full of drives and stuff. No more sketchy-ass molex to SATA adapters with floaty pins that fall out like crackhead teeth- in fact, I think I might have fried a pair of SSDs with one. Avoid. I will be thoroughly documenting my findings in this thread so that future people can learn from my probable mistakes.
Have any of you guys done this already? I'm wondering if I'll need a 3D printed bracket or if zip ties will suffice, but I guess we'll just have to wait and see the dimensions on the new PSU.

 

[joevt]

Modern power supplies have more current for +12V but may have less current for other voltages (-12, +5).
What does your MDD power supply support?

Have you chosen an SFX power supply yet?

 

[jovianartifact]

Dunno, I was just gonna pick one off the shelf I figured “standard is standard”, especially CHRP remnants. I’ll have to take a look.

 

[Juror22]

I will be thoroughly documenting my findings in this thread so that future people can learn from my probable mistakes.

Looking forward to this! I have 4 MDDs (all on their original PSU and fine so far) that will need attention in that area eventually, so it will be instructive to see what you encounter/overcome to get this solution working.

 

[jovianartifact]

I'm finding that most SFX power supplies have either no -12v rail at all, or it is rated at .3A, just shy of the .4A rating on the stock PSU.
There is also a +25v rail on the stock PSU, but I assume this is for ADC power; am I correct in this assumption?
I will post a picture of my stock PSU and the one I plan on replacing it with in some hours.

 

[s_pupp]

I'm finding that most SFX power supplies have either no -12v rail at all, or it is rated at .3A, just shy of the .4A rating on the stock PSU.
There is also a +25v rail on the stock PSU, but I assume this is for ADC power; am I correct in this assumption?
I will post a picture of my stock PSU and the one I plan on replacing it with in some hours.

ADC power is correct.
I had a full sized ATX PSU sitting on top of my MDD G4 for a few years. I don't use ADC, and so there were no issues with the loss of the 25V line. If needed, a boost DC-DC converter could provide the 25V needed for ADC.

 

[jovianartifact]

This is the sticker on the original PSU and the link is the transplant candidate. Everything looks to be more than adequate on the spec sheet. I didn’t really want to spend nearly that much, but it’s the only one I found that has -12v, >=.4A. Ugh. Guess I’ll be saving my pennies.

https://www.newegg.com/asus-rog-loki-rog-loki-750p-sfx-l-gaming-750-w-80-plus-platinum-certified/p/N82E16817320037

 

[greystash]

I did this conversion last year, but didn't make any adjustments for ADC (since I don't use it). I also added test details on graphics cards that work with the PSU I selected. Without the ADC accommodations some of them caused issues:

Mac Classic

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The NVIDIA GeForce4 MX 440 was the most friendly card I tested that didn't have any issues with the new PSU. The machine is still going strong and has been much more stable and quiet

 

[jovianartifact]

So you’re saying that EVEN IF you don’t use ADC, without 25v these cards just… don’t work? Wonderful. But wait, s_pupp said he had no problems without 25v… what could cause this disparity in results? This is appearing to be much more complex than I initially believed, and I really thought I did my research.

EDIT: after looking at the spec sheet for greystash’s Silverstone SX650G, I noticed that it’s -12v rail is .3A; just shy of the .4A rating on mine. Could that be the culprit? Idts, but I thought it worth mentioning. S_pupp, does your PSU provide at least .4A on the -12v rail?

 

[s_pupp]

So you’re saying that EVEN IF you don’t use ADC, without 25v these cards just… don’t work? Wonderful. But wait, s_pupp said he had no problems without 25v… what could cause this disparity in results? This is appearing to be much more complex than I initially believed, and I really thought I did my research.

EDIT: after looking at the spec sheet for greystash’s Silverstone SX650G, I noticed that it’s -12v rail is .3A; just shy of the .4A rating on mine. Could that be the culprit? Idts, but I thought it worth mentioning. S_pupp, does your PSU provide at least .4A on the -12v rail?

My PSU provides 0.5A at -12V. It is a Cooler Master RS-600-AMBA-D3.
The graphics card I was using for its VGA output was an OEM Radeon 7500, which I believe also has an ADC port.

 

[joevt]

EDIT: after looking at the spec sheet for greystash’s Silverstone SX650G, I noticed that it’s -12v rail is .3A; just shy of the .4A rating on mine. Could that be the culprit? Idts, but I thought it worth mentioning. S_pupp, does your PSU provide at least .4A on the -12v rail?

Probably your Mac doesn't use all 0.4A of the -12V rail of the power supply? Check with a current meter?
-12V is used for PCI (100 mA each) and serial ports and floppy disk drives?
AGP doesn't have -12V.

0.4A = 400 mA. MDD has 4 PCI slots = 400 mA.

 

[jovianartifact]

Probably your Mac doesn't use all 0.4A of the -12V rail of the power supply? Check with a current meter?
-12V is used for PCI (100 mA each) and serial ports and floppy disk drives?
AGP doesn't have -12V.

0.4A = 400 mA. MDD has 4 PCI slots = 400 mA.

Oh it sure will use all that power that is, if this actually comes to fruition. I would really like to figure out what causes some cards to work and not others, especially since I have a Radeon 9000 that is listed as non working, and I can’t really justify buying even more hardware for this. I guess I should just buy the dang PSU and if it doesn’t work, then it doesn’t.

 

[jovianartifact]

oops

 

[jovianartifact]

My PSU provides 0.5A at -12V. It is a Cooler Master RS-600-AMBA-D3.
The graphics card I was using for its VGA output was an OEM Radeon 7500, which I believe also has an ADC port.

Hmm. The fact that yours is over the stock amperage tells me that that very well may be the culprit, despite not being able to control for other variables. It just doesn’t make sense though if that -12v rail has nothing to do with AGP. I will have to just take the plunge then, I suppose.

 

[joevt]

Hmm. The fact that yours is over the stock amperage tells me that that very well may be the culprit, despite not being able to control for other variables. It just doesn’t make sense though if that -12v rail has nothing to do with AGP. I will have to just take the plunge then, I suppose.

Are you saying that substituting a power supply that supports more current than the stock power supply is a problem? Because that's not how current works. The power supply will supply only as much current as the loads connected to the power supply require. If the loads take too much current, then the power supply is expected to turn itself off.

Or maybe you are referring to a different post where the new power supply supports less current than the stock power supply and has a problem because of that?

Oh it sure will use all that power that is, if this actually comes to fruition. I would really like to figure out what causes some cards to work and not others, especially since I have a Radeon 9000 that is listed as non working, and I can’t really justify buying even more hardware for this. I guess I should just buy the dang PSU and if it doesn’t work, then it doesn’t.

A PCI device is allowed to take up to 100 mA from -12V. That doesn't mean it will.

 

[jovianartifact]

No, I was just pointing out that it seems the guy with the -12v >.4A PSU doesn’t have problems with his video card, while the guy with less than .4A does. I know it doesn’t make sense but that’s what we’re seeing here. I will have to test and see if my Radeon 9k does indeed not work without 25v.

 

[quinterro]

Last year I found a MDD 1.25ghz G4 at the thrift store, but the power supply was dead.

I ordered a ATX adapter cable and a SFF ATX power supply. It works, but I have the power cord going through the hole it would originally have plugged into the power supply from into the new power supply. I just leave the cord connected, but it's easy enough to open the case and disconnect it if needed. The power supply is attached to the frame above the optical drive with 3M Command Strips.

When I took the MDD apart for cleaning, the motherboard appeared to be stuck to the case. Because of the amount of pressure I had to apply to finally free the motherboard, I ripped a capacitor and one of its traces off of it. The G4 now has a slightly older motherboard and a dual 800mhz G4 processor. Eventually I'll solder a bodge wire to fix the damaged trace and get the original board and processor back in the case.

It still has the original ATI Radeon 9000 AGP card in it.

 

[chelseayr]

I know its not adc but remind me if I'm wrong, didn't some/all g4's also depend on a direct psu tap for the firewire ports too? I forgot if this was where 24v came from too or it rather was just the more common 12v rails being tapped from instead

 

[quinterro]

I know its not adc but remind me if I'm wrong, didn't some/all g4's also depend on a direct psu tap for the firewire ports too? I forgot if this was where 24v came from too or it rather was just the more common 12v rails being tapped from instead

I have no clue, but also have no FireWire devices either. All external devices I have are either USB or eSATA.