Gigabit ATX

Very useful to know, esp. as I've got an unused gigE MLB I'd like to put into service.

dan k

I just did the same thing, it works fine.

You should keep in mind that the 28 volts if for the firewire devices, too, so bus powered firewire devices won't work on your system after this hack.

There was recently discussion about this on one of the LEM e-mail lists, their solution was to use a pair of diodes, one from the 5vsb and one from a 12v line, so that the 28v trickle input to the motherboard got 5v trickle until turned on, then got 12v once on. 12v should be enough for Firewire drives, and if you use a large enough diode, there should be no problems of power draw.

I too read the LEM discussion but haven't the clue to decipher what exactly the recommendation entailed. Can anyone draw me (and anyone else who got lost) a picture how the 5v/12v + diodes thingies would be laid out? Well, and some ideas on exactly what sort of diodes one might use? I can wire up all sorts of crap but have dim prospects without some explicit advice.

mucho TIA,

dan k

I haven't read that discussion but I assume that it will look like this.

The diodes are there to stop the supplies loading each other.

As for what type, they must have a revers voltage of more than 12v and able handle 2 or 3 amps. It depends what firewire devises you are using.

edit :-

Just looked at my GE power supply and it can supply 4.04 amps at 28v, so you might wont the diodes to handle more current.

ketil b

The 4 amps rating is for when used with an Apple Studio Display CRT. Those things suck up the power (and probably are a big part of the reason the power supplies are prone to dying)

For firewire devices, you wouldn't need nearly as much power. I just used 2 diodes that were part of a bridge kit from Radioshack, 6 Amp rated. I'm trying to find a cheapo FW case and hard drive to use for testing.

Hey, thanks guys for the details. I just don't know enough electronics to figger even diode usage.

What's a bridge? A rectifier? Got a RatShack part number?

dan k

A bridge/rectifier is what's used in switching power supplies (non-transformer) to change from AC voltage to DC voltage. (They're also used in transformer power supplies, but not always needed). A bridge/rectifier is basically 4 diodes working together.

As you know, a diode limits the direction current can flow. AC current flows in both directions. By using a bridge, or 4 diodes, you can get DC power out of both flows of AC. Here's some additional information http://www.answers.com/topic/diode-bridge

These are the diodes I've been using for testing. They're 6 amps rated, and I assume that since they're made for bridges, they'll do well to restrict 5/12v. Honestly, I don't know all that much about electronic components, namely the specs on items. (Reverse voltage).

I'm assuming that for an adapter like for this case, the 5vsb line wouldn't need a full 6 amps, would maybe 3 do fine?

Now, one thing I have to wonder about... Deep Sleep? How does that run? I'm almost afraid to test it because I'm almost certain it runs on the 28v trickle line, and that's probably going to cause some issue.

My system is fine in deep sleep. This might not be the case if you are running lots for USB and firewire devises that are bus powered and can wake up the system, because the only power available in deep sleep is the 5v SB (assuming you are using an ATX supply), which is limited at 2.5A continues with a max spike of 3.5A.

I think the only problems that we will encounter using 5v instead of 28v will be with subsystem that use more than 5v (ACD and firewire) all the other systems will be powered from a 5v regulator on the mobo, so as long as that has 5v or more it will give out 5v and the mobo will be happy.

Reverse voltage is the voltage the diode can stop befor the n-p junction is the diode breaks down.

Hope all that makes sense

Ketil b

I've been working with this idea for a while now, I was going to try building adapters for the 28v mod, but this came along just in time. I bought twenty ATX 20->24 pin adapters just a few days ago, they arrived yesterday. I have adapted the first one and have pictures of it used with a Micro ATX power supply taken out of an old HP Pavilion PC.

http://ninjaproduction.com/ATXG4/100_2603.jpg
http://ninjaproduction.com/ATXG4/100_2605.jpg

Obviously with that being the test model, it's a bit crude. I'm working on ideas of how to make it look better and which parts to get to make it easier to build.

Would 3 Amp diodes suffice? Any specific type? The ones I'm using are rectifier diodes, 6 Amp, with 200 PIV I believe. I was going to go down to 3 amp with 50 PIV, which seems as though should work just fine. The 6 Amp diodes have extremely large leads to attach to the harness wiring, I'm hoping the 3 Amp diodes will be much more manageable. I'm also trying to find ideas for better connections. I like the crimp pieces I used on this adapter, but they don't really look nice. I'm hoping that with the 3 amp diodes, I'll be able to twist the wire with the diode, then solder, finally add some heatshrink overtop, and be done with it. But if that solution doesn't work out right, any other suggestions would be welcome.

Sorry fir the not replying sooner.

the type of diode doesn't mater to much to much, as long as the current rating is high than the current you are pulling.

If you are not using firewire then you don't need the diode, if you are using firewire then it would be a good idea to dig out the specs for firewire and find out what the max current is on a firewire port.

As a guess and this is only a guess because I have not seen the firewire specs. That 3A would be fine.

In my hack I used the heat-shrink method that you describe. I think this is the best way, its neat and ease to do.

ketil b

p.s. if you do find the firewire specs I would interested to see it.

p.p.s. in the pic in the Grim Ninja's post there is 10 big solder pads to the left of the heat-sink, any one know what they are for.

Just replaced the original power supply in my GE Mac with an Targan 420W ATX PSU.
I have used a power extension cable to reroute the wiring and applied the diode solution to feed the 28VSB line.
This mod was necessary after upgrading the Mac with Gigadesigns Dual 7455 1.4GHz and ATI Radeon 9800 Pro, as original power supplier would shut down under full load.
Since the modification, I am observing some peculiarities.
First, every time I start up the Mac I get the warning that my clock has been set to a date before 2001. I first thought, that the PRAM battery was drained, but it still shows 3,65V under load.
Secondly, I can't put my mac to sleep. It only sends the graphics and the hard disks to sleep but won't shut down the processors.
I suspect, these two things are connected and have to do with feeding 12V into the 28VSB.

Has anyone experienced this type of behavior after the modification?
I think, I could figure out, what the problem is, if I had some circuit diagrams from the motherboard, which indicate for what the orginial 28VSB are used resp. connected to.

Any ideas or comments are highly appreciated

Jens

Did you try the hack with the stock processor?

I have a feeling that the problems you are having are to do with the Gigadesigns card.

Ketil b

Does your system wake up from sleep? (without any problems?)

It's quite possible that the gigadesigns card doesn't support deep sleep in the first place.

Also, the success of deep sleep with the ATX modification is completely dependent on the power supply you use as your replacement. I've used some power supplies which have a glitch where the first sleep attempt fails, wakes right back up, but further attempts are perfect. I have another supply which had USB glitching, and would constantly wake back up. The B&W G3 power supply I modified is 100% fine as are the two Thermaltake and the Antec power supplies that were tested.

The 28v line is regulated to 5v for the PRAM, 5v for the system memory (during sleep), 12v for the video card (in some systems, so far I only notice it in the Quicksilvers), it's unregulated for the Firewire power and also for the ADC power.

Thanks for the hints. I had been running the Gigadesgins card for almost two years with
the original PSU and deep sleep did work, although it created stranges noise during initiation sometimes.

If indeed the 28v feeds into a 5v voltage regulator, this may cause an issue. Using a diode and a 5v supply will only provide 4,3V to the 5v regulator (silicon diodes have a voltage frop of 0,7v). I suspect this may cause the issue with the clock.

I´ll try to run some test with a seperate power supply to verify.

Has anyone, who applied the diode solution experienced similar issues.