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Two dead G4s

I managed to swap out the pins in the extension cable using a sewing needle. Pretty easy actually!

I hit the power button and it lit up for a split second then went off again. There was also a short pop from the speaker like it was getting power. The red led on the mobo flashed on for a second but isn't staying lit.

Now to figure out what's stopping it from sparking up the whole way. There's no PRAM battery, could that be the cause?

 
Well, I tried all three PSUs. With the two 300W ones the brief bit of life was a little briefer and there was no pop from the speaker. I tried a PMU reset as well. But it still won't fire up.

 
Make sure you are cutting off/removing the -5v line coming from the PSU, that sounds like what happens when I have accidentally not disconnected it.

 
Oh the -5V has to go? I thought it was just a case of redirecting the +5vSB to the +28v.

Ah I see now. Looking at that page the -5V is a ground on the G4 PSU.

 
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Yea, that pin on most G4s is a ground on the motherboard, so you are grounding out the -5v and the PSU does not like that.

Hopefully we hear you reporting successful booting in a moment here. Good luck. :)

 
It's aliiiive!

I didn't get a chime but it's booting to the flashing system folder (there's no hard disks in this yet).

Now I just have to get this tidied up a little. I still have to remove the -5v and +5vSB wires from the other end of the extension cable. Just can't figure out how to remove the pins from that side.

 
Sure does. And considering the reliability of the original PSUs it's nice knowing that I can now swap in any ATX one.

And in true hacker fashion it's 3.30am so I'm gonna call it a night. Tomorrow I clean out the dust bunnies, hook up the fan, see if I can get rid of these couple of wires on the extension cable, pop in a 80gb Seagate drive I have in the room and get playing with my new toy :D

 
I had to drop back to one of the 300W PSUs as the connections on the 400W wouldn't fit flush with the back of the case. It's just on its first proper power-up. I've popped in a 80gb hard disk, hooked up everything and booted off the AHT disc I downloaded from Apple. It's just passed the extended hardware test.

I was toying with the idea of swapping out the case fan for a PC one which would have had a standard fan header. But while rummaging around in my magic box of cables I found a cable that had the same "fan" connector that was on the original PSU. So I popped one end of it and stuck the wires into a couple of molex pins and made a molex fan adaptor.

Surprisingly the PRAM battery is actually still OK. It even looks like it might be the original one (one of those green SAFT ones). Only thing that's puzzling me right now is I'm still not getting a startup chime. But for now the next step is to tidy up the cabling inside.

 
For a unknown period of time a while ago my G4s (both Sawtooth and DA mobos) would not chime but now I know my DA does. not sure about the Sawtooth anymore.

The only thing I think changed was the PSU.. I was using the same PCI/AGP cards in both and the same drives in both(same internal and external speakers too) but now I have a different PSU in the DA+the dell lappy adapter(not really using the Sawtooth anymore)

I know that the internal speaker output of the Sawtooth has basically failed while my dad was using it(it made noise when you put it to sleep and how loud+frequency drop rate depended on how long it was running) But the DA's internal speaker output is ok.

But yea, I never figured it out and cannot remember when they stopped chiming and when they began chiming again. This is of course presuming that the Sawtooth now chimes like the DA... *shrug*

 
Oh the -5V has to go? I thought it was just a case of redirecting the +5vSB to the +28v.
Ah I see now. Looking at that page the -5V is a ground on the G4 PSU.
Click to expand...
You powered it up without even looking at the pinout? :O

 
I bet he did the rest but forgot about the -5v. But yes, he should have examined everything more closely.

At least nothing got toasted though.

 
You powered it up without even looking at the pinout? :O
Click to expand...
Hey I'm new to all this! Plus it was late and most of my thinking faculties had gone to bed for the night. I did look at the pinout but I was mainly concentrating on the +5vSB pin. Anyway it all worked out good in the end, thankfully.

I've bunched up three of the sets of cables coming from the PSU, tied them and wedged them in behind the fan bracket to keep them out of the way. Whoever took out the hard drives also took the hard drive caddy for the IDE drive. So I used the middle hard drive carrier and placed some little dampeners between the carrier and the drive to help with any vibration. I dug out the horrible, horrible pair of "pc speakers" I got with my first PC. Should do the trick for hearing sound out of the line out for now.

So now I finally have my first G4. A whole new world of Altivec awesomeness unfolds.

OK, with the speakers plugged in I hear a faint chime, so there must be something up with the internal speaker. Something to look into later...

 
Thanks :)

I didn't get to spend much time on it yesterday but a couple of notable things happened. The chime came back (intermittently) so the speaker is working fine.

On the not-so-good side, at one stage the hard disk started powering down and back up again (like when its not getting enough power). I hit the reset switch and it stayed powered on. It may have been a glitch of some kind but if it happens again I wonder if it might point to the 300w PSU not being up to the task. I also ran MacTest Pro on it and it failed some of the Video tests in the logic board section. It may have been running the wrong tests I'll have to double-check as it was late when I was doing this. Everything else passed OK and video is working fine (passed the AHT tests).

I ran the test again and I think the logic board test may be a little flaky. If I deselect all the logic board tests and run each video test individually they all pass. But if I try to run all of the video tests it fails on the second one (Video DAC Read/Write).

 
Seeing as the ATX transplant worked so well with the GE I was wondering if anyone has ever tried putting the guts of a 1U server PSU into the MDD's PSU casing for a perfect fit replacement? Or maybe there's a 1U unit that would fit nicely in it's place? Shoehorning in a regular ATX PSU doesn't look that great.

It was asked here but nobody gave an answer. However there is a quote that seems to shed light on why these PSUs were so prone to failure.

 
That's very interesting. I can't imagine why it would continue to pull from the +28V when it's off. I resurrected my MDD with an ATX mod and nothing going to the +28V pin at all and it works just fine (minus ADC and powered firewire) Was it Just a design flaw?

 
That's very interesting. I can't imagine why it would continue to pull from the +28V when it's off.
Click to expand...
because on those models the 28v is also the standby.
I resurrected my MDD with an ATX mod and nothing going to the +28V pin at all and it works just fine (minus ADC and powered firewire) Was it Just a design flaw?
Click to expand...
MDD has a normal 5v standby and separate 28v. Apple might have noticed the overheating while off issue and decided to fix it the proper way.
 
Congrats on the successful repairs. :D

My startup-chime disappeared when I installed linux on my Sawtooth. Apparently setting a non Mac OS drive as the default boot disk does something. I got it working again at one point when I reset the PRAM. (But then I installed a new linux OS.) Maybe resetting the PRAM will get your startup-chime working. :D

 
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