G4 Gigabit Ethernet - Power Supply Questions

[TheNixer]

After much deliberation, I've purchased a badly needed video card upgrade for my G4 GE. I bought a 128mb Radeon 9800 Pro PC edition. It isn't here yet but it's on the way. I've also got a few cards in the machine:

Slot B: SCSI Card

Slot C: 4-Port USB Card

Slot D: SeriTek ATA Card

It's also got an Airport card but big power consumers besides the cards are the hard drives. The ATA card powers two 200gb drives. Those two along with two 120gb drives makes four. There's a lot of stuff in this machine and I'm afraid the addition of the new video card may be too much.

ADC causes problems with stock PC power supplies, from what I've read. Do you think this is too much for the stock PS and if so, has anyone replaced their GE (or newer) G4 with a new power supply and had good results?

Thanks!

 

[Quadraman]

Some people say you can substitute a 12v signal on the 28v line just to get the machine to boot but you can't use ADC monitors without the proper 28v. If you aren't using an ADC monitor, you should be fine, but I haven't tried it. Someone here does have a G4 running with an ATX supply, but I can't remember who it is at the moment.

 

[Bunsen]

Mine boots just fine with the +5VSB (standby power) connector from an ATX supply in place of the +28V (and other neccesary pin remappings as detailed on the frankenmac G4 site). You can't use an ADC monitor or any bus-powered Firewire devices, unless you get a powered Firewire hub. If I end up with anything that needs power on FW, I might try a spare +24V Powerbook PS.

 

[tomlee59]

That's very helpful information. Thanks, Bunsen!

 

[TheNixer]

Yes Bunsen, thanks! I have an ADC to DVI adapter that allows an ADC to plug into the wall instead of drawing from the computer, so that would allow me to use ADC anyway, I suppose.

If you don't mind, what power supply did you use? I'd like to not tamper with the case too much.

Thanks!!!

 

[trag]

A little circuit to convert 5V to 28V...

http://www.io.com/~trag/28v_vreg.pdf

I did not create this circuit, but it is a very standard application/use of the National Semi part.

When the computer is powered off, the 28V circuit draws current off of the 5V standby circuit, so it is good to choose an ATX power supply with a reasonably beefy standby current capacity. After the machine is turned on, all of the 5V current should be available to the 28V converter. However, the chip used here is only good up to .3A at 28V. If you have an ADC display which needs to draw more power, then you should choose a beefier booster chip from National Semi. If you visit their site it is pretty easy to get to a table which will show you the relative specs of their family of booster chips, including the max amperage available after conversion. I think there are chips which go up to 3A.

 

[TheNixer]

Thanks trag! I just made a pretty long post about not being able to get around the 28v "trickle" needed for this board. I actually screwed up and blew the stock PS, but I did my best to prevent it. I'm pretty sure this PS wouldn't run the card, just the card. It wouldn't do it with one hard drive and the card. I mean, it blew it immediately.

I'm back up and running with another stock 22 pin PS...without the extra video RAM.

I'll take a look at what you've got there, I really appreciate the info.