do pc ps's work in G4 apply macs?

  • Thread starter Thread starter ~AlicGinnis~
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A

~AlicGinnis~

I agreed to take a shot at an Apple G4 Power Mac circa 2001 that's broken.
Pushing the go button gives nothing, so I'm starting at the power supply.
Its 344 watts, made in china. Thing is, I never looked at an Apple before.
It looks like an ATX supply to me, you know, the kind witht the little
square 4pin molex along with the regular mobo connector. Are the Apple
power supplies the same as you use in a PC?
It looks like it is. Normally I'd short the green wire to a black one to
see if it comes on, but I don't know if this is wired the same way, and
don't want to accidentally smoke it, etc.
Thanks for any info.
Al
 
After some googling it looks like all apple power
supplies are propriatary and are not interchangable between various models,
and they are not re-badged
ATX supplies.
If I'm wrong about this, please advise,
thanks.
 
~AlicGinnis~ said:
After some googling it looks like all apple power
supplies are propriatary and are not interchangable between various models,
and they are not re-badged
ATX supplies.
If I'm wrong about this, please advise,
thanks.
Click to expand...

Apple certainly does stuff like that.

First, you have to identify what Mac you're looking at.

http://en.wikipedia.org/wiki/List_of_Macintosh_models_by_case_type

That page doesn't have every case depicted. For example, under
the G4 image, there is a link to more PowerMac G4 images. I've
got a Mirror Drive Door (MDD) machine here, known affectionately
as the "Quad Nostril".

http://en.wikipedia.org/wiki/Power_Mac_G4

Once you have a decent identification of the machine, you
can look on sites like xlr8yourmac.com , to find articles
on power supplies, and how to convert a PC power supply
to run a Mac. For the ADC connector, I don't know right off
hand, whether there are any other dependencies other than
running an Apple monitor. If the ADC power rail was not
used by any other hardware, then using a PC power supply
to run one, would simply prevent ADC monitors from working,
but with the appropriate adapter (ADC to whatever), perhaps
other monitors would continue to work.

A sample article.

http://www.xlr8yourmac.com/tips/MDD_ps_mods/MDD_PS_Mods.html

Since the case on mine is modded, I cannot open it right
now and say more about what is inside :-) I fitted a fan
below the PCI card slots and changed the airflow pattern
to get better cooling. Air flows in through the perforated
slot covers on my machine, then out through the lower part
of the vented area on the back. And the nostrils actually
breathe in. It is my attempt to get a more PC-like, front
to back airflow.

Some things the computer would share with a PC, would be
the existence of a CMOS battery. It won't be quite the
same as a CR2032, and may be a cylinder shaped one. The
computer power supply may also have a +5VSB equivalent,
which in the above sample article, they call "+5V TRKL"
which stands for "trickle" as in trickle charging. A
trickle of current is needed, for a sleeping computer. If
that was dead for example, that might be enough to prevent
the switch from turning on the computer. (The ATX supply
has two halves, one providing +5VSB, and that +5VSB is
used to supervise the operation of the main part of
the supply. If +5VSB is dead, the main supply cannot
start.)

There is also a "CUDA reset", where the CUDA is some
kind of supervisory controller. The power switch may
be routed through that. (It's been a long time since
I had to worry about Macs, and there is lots of
trivia.)

More on CUDA here. CUDA varies from Mac to Mac, in
terms of its functions.

http://support.apple.com/kb/HT1939

USENET has Mac newsgroups, but the folks who used
to hang out at xlr8yourmac.com knew a lot more
about hardware and hacking it. There used to be
a forum there, but it closed some time ago. The
forum software was not very robust.

Good luck,
Paul
 
Hey Paul, thanks for the therough reply! I will get on it. So far I have
found the answer to your first suggentsion: find out exactly what it is.
Its a Power Mac G4 (QuickSilver),
887 Mhz, PC133, 60 GB hd, 4X AGP, 3 memory slots, 2 fire wire, 2 usb, and 4
pci slots, all empty.
Al
 
~AlicGinnis~ said:
Hey Paul, thanks for the therough reply! I will get on it. So far I have
found the answer to your first suggentsion: find out exactly what it is.
Its a Power Mac G4 (QuickSilver),
887 Mhz, PC133, 60 GB hd, 4X AGP, 3 memory slots, 2 fire wire, 2 usb, and 4
pci slots, all empty.
Al
Click to expand...

I'd probably start, by monitoring what the thing "Pin 15 (Power On)"
is doing, when you push the button on the front. The only standby-type
voltage shown in that pinout, is "Pin22 +25V Trickle", and that
makes it different than the way an ATX supply works. Something
has to power enough of the logic, like the CUDA, to drive the
"Power On" signal when needed, and the trick will be figuring
out how that works. I'm wondering if the labels on the pinout
here are accurate.

http://www.xlr8yourmac.com/tips/MDD_ps_mods/PS_QS.gif

You should get some hint, by using your multimeter, and measuring
the potential on each pin while the computer is sleeping. If the
labels on that diagram are correct, you'd expect to see +25V on
pin 22. And you'd expect to see a logic level (between 0 and 5V)
on the "Power On" signal. (On a PC, zero volts is ON, while
a 5V level is OFF.) Apple would be free to do anything
they like of course, so if they wanted, they could use a 25V
logic swing on the "Power On" signal. It all depends, on how
much of an excursion from normal ATX design, the power supply
maker has to make, to give the new rails and features.

I'd have to set my voltmeter to the 100V scale, to work
in there :-) Nobody really enjoys working with stuff like
+25V. It was just a silly idea on Apple's part, and I don't
think they do that any more on their newest products.

Paul
 
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