MDD G4 not powering on. Please help. Am i screwed?

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TheUltimateMacUser's picture
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I was using my Dual 1.25 GHZ MDD G4 the other day.
It decided to go into sleep mode on it's own. Any attempts to wake it up resulted in it going back into sleep mode right away.
It could not be woken up at all. Anyway, now it won't eeven power on!
When i try toturn it on, the power LED blinks once, breefly. That's it. Nothing else happens.
The Power LED will not flash again until the machine has been unplugged, plugged back in, and reset.

Any advice greatly appricated, as i really need this machined working properly.

Thanks in advance.

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eeun's picture
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I'd first pull and re-insert

I'd first pull and re-insert cables, CPU and ram, if you haven't already. Always eliminate the easy stuff first. Laughing out loud

Remote troubleshooting like this is always a crapshoot, but the PSU is the MDD's weak spot, so I'd check there next.

A blown power supply can give you a brief glow on the power button like you describe, while not letting the system fully power up.

Pull the PSU and check for scorch marks under the shielding. Also look for bulging or leaking caps.

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cwsmith's picture
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Dead PRAM battery?

Check it with a voltmeter: if under 3V, replace it.

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TheUltimateMacUser's picture
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Righto

I've already field stripped the machine. Removed everything (unplugged IDE cables, too cpu out, ram out, PCI & AGP cards out, etc... and put everything back together.

I'll check the battery next, and if that is okay, i'll examine the PSU.

Will report back.

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cwsmith's picture
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Thermal pads/paste

If removing the heatsink/CPU from the logic board, please don't forget to remove and replace the thermal material between them.

Poor heat transfer = Release of magic smoke

Ask me how I know! Sad

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Dozens of Macs; a handful of PCs; Apple ][e, ][c and ][gs; a few iPods; lots of parts
17 guitars, 2 baritone guitars, alto guitar, 6 bass guitars, bajo sexto, 3 ukuleles, mandolin, banjo, sitar
3/4 scale upright bass, 4pc drum kit, congas, travel congas, bongos, cajon, cabasa, 12 harmonicas
http://www.cwsmith.fmhttp://www.facebook.com/cwsmith2620

TheUltimateMacUser's picture
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Got it

I know... already done. I'll fiddle with it more tomorrow.

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TheUltimateMacUser's picture
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...

Pram battery is fine. 3.6 volts registered on my volt meter.

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TheUltimateMacUser's picture
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Ant the PSU...

And the PSU looked fine. No scorch marks of other obvious damage to any components.

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TheUltimateMacUser's picture
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Heh...

I'm in my local Apple store right now, they are looking at it.

... Posted from my iPad.

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Hawaii Cruiser's picture
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My wild guess: bad video card

My wild guess: bad video card or video card connection.

TheUltimateMacUser's picture
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The Genius Bar people said it

The Genius Bar people said it was the logic board.

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Hawaii Cruiser's picture
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sure

Ah shucks, dey always say dat.

TheUltimateMacUser's picture
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Re: sure

Hawaii Cruiser wrote:

Ah shucks, dey always say dat.

You think they were blowing smoke up my arse?

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eeun's picture
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It [i]could[/i] be the logic

It could be the logic board, but as HC says, speaking generally these guys are likely not much better qualified to diagnose hardware issues than you are. They might be right, it might be the CPU, it might be the PSU. Unless they told you why it's the logic board and how they determined that, I'd remain skeptical.

What you decide to do should be based on how much the MDD is worth to you. If you're up to it, you could try wiring up an ATX PSU just to test their diagnosis.

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TheUltimateMacUser's picture
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It's...

It is worth it to me to try to get the MDD working again as i haven't got the money to spend on a new computer at the moment.

If someone wants to send me $600 I'll walk int the Apple store and buy a new Mini tomorrow.

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It's the power supply. It's always the power supply.

Those things always crap out on the MDD.

There are some guides for replacing the PS with a standard ATX power supply. Never could get mine to work because I was using an outdated guide that had the wires written backwards and I think I fried something. Ended up trading it + a working unit for an iPhone 3g + a 32gig ipod video to some "producer" kids last year.

I definitely got the better end of that deal.

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Re: It's...

TheUltimateMacUser wrote:

If someone wants to send me $600 I'll walk int the Apple store and buy a new Mini tomorrow.

They're $700 now...

TheUltimateMacUser's picture
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Hmm...

If i take the CPU daughtercard out, and try to power the machine on, it behaves differently. The Power LED comes on, then slowly fades out. Subsequent attempts result in the same behavior.

With the CPU daughtercard IN, it reverts to the old behavior of the power LED coming on briefly, and the fans flicking for a second, with subsequent attempts resultingt in nothing.

So... Bad logic board, or bad CPU module?

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eeun's picture
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Confirmed that's what mine do

Confirmed that's what mine does with no CPU. So your logic board is at least doing what it should when no CPU is present.
Unfortunately, that doesn't nail down the cause.

My money is still on the power supply. When the MDD PSU failed, the tendency was for some power to still be available, but it's unable to maintain the current required by the computer to boot up and/or stay booted.

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TheUltimateMacUser's picture
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No...

It isn't the power supply. I tested it; it's fine... Suppling all the varying voltages it should.

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if it's not the power supply
TheUltimateMacUser's picture
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Just checking...

Just to be sure... There isn't a difference between the logic boards used for single CPU 1.25 GHz machine and the dual CPU 1.25 GHz machine, right?

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eeun's picture
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yes

Yup. Both single and dual 1.25 MDDs use the same board.

The 867 MHz single CPU had a slower bus, and the FW800...well, you know.

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TheUltimateMacUser's picture
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Replacement board ordered fro

Replacement board ordered from fleebay.

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Any news?

Did your board come in yet?

TheUltimateMacUser's picture
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I'll be able to report on the

I'll be able to report on the condition of the machine later this week. Been out of town.

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NewS?

I'm dying to know!

TheUltimateMacUser's picture
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well...

As you asked... here is an update:

IT'S ALLIIIIIIIIIIIVE!!!!!!!!! Laughing out loud

I've just got 'er working again a few minutes ago.

For the record, it was the CPU daughter-card. I had to jump through all sorts of hoops to get the right replacment part, and i've just not got the machine going again. It's been successfully booted for about 15 minutes with nary a hiccup. I am soo effing happy right now, i'm going to need a grinectimy.

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I don't get it. I thought you

I don't get it. I thought you ordered a motherboard, not a CPU card. What happened with the motherboard and where'd the new CPU come from? More than any other machine I've ever owned, I've learned to never count my chickens early, and actually, not at all, with my dual 1.25 MDD. Stability always seems to be a work in progress, never truly accomplished. It crashed on me three times this morning while I was watching online video. I suspect the MDD never really belonged in a G4 graphite case. It simply cannot cool well enough in there. I had a Dell 9150 case that would have been perfect for it (reverse ATX design), but the AGP and PCI slots on the MDD motherboard are placed along an indention, so there's no PC case that will work.

TheUltimateMacUser's picture
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I ordered a motherboard, as p

I ordered a motherboard, as per the advice of the guy at the Apple store. That didn't fix it. Then, based on the fact that it had shut itself down just before it stopped working, i did what i should have done in the first place and ordered a new CPU board. That is what fixed it.

The upshot of which is that i now have an extra logic board lying around that i can resell and perhaps get some of my money back. Either way... my machine works, and i was able to get a pretty good deal on both transactions, so... i'm happy.

PS: Anyone want a MDD G4 Logic Board? Tongue

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