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Two dead G4s

protocol7

protocol7

6502
I was given a couple of PMG4s earlier and I've been spending a little time trying to get either of them to power on.

First up is a 2x1.25GHz MDD 2003 and the second is an old 450MHz AGP Graphics. Both have seen better days. Hard drives and RAM are missing and the AGP model shows some signs of rust and corrosion on the ports at the back. The MDD blew the fuse in the power cord when I fired it up so I've been focussing on the AGP first. I've pulled the SCSI card, leaving just the AGP card in, put in a stick of PC100 SDRAM and reset the PMU but still no signs of life. Also took out the PRAM battery because I figured it's probably dead. I swapped the AGP card for the one in the MDD in case it might be to blame, but still no change (unless they're both toast).

According to the service manual there's a red LED that shows if the board is getting power. Alas, it neglects to mention where on the board it is (the diagram just shows the LEDs for the PCI Graphics model) but I can't see any red LED lit up so I guess I'm looking at a dead PSU or board here?

Does anybody have any suggestions on what I should look out for or try? It'd be nice to get these working again.

 
Tried the MDD again and sure enough pop goes another power cord. I googled the PSU part number 614-0224 and seems these had a habit of blowing. Would explain why the only cheap ones on ebay are dead. So the MDD goes in the "someday" pile. Maybe there's a chance to resurrect the 450 though?

 
Thanks MacJunky. It definitely wasn't on (as you said, I'd have seen it). I'll check out the PSUs with a voltmeter at some stage when I can borrow one, but I've thrown in the towel for now as I'm sure they're both kaput and there's no sense in buying replacements.

 
Thanks again. I've bookmarked that one for future reference. The AGP turned out to be a Gigabit Ethernet so it's not as easy a fix but it's good to know these things for the future. I'll look into the possibility of fixing the MDD one. There's a lot of good info on badcaps.com if you can make sense of it all (I can't but I know someone who might).

 
If you are cautious of cutting a cable and wiring it up or w/e (from what I've seen of diagrams it is really easy and I think just a rewire and a fuse or something added?). Their is a site that sells pre modded cables. Seems like the MDD would be the easiest/best machine to fix up :)

 
(from what I've seen of diagrams it is really easy and I think just a rewire and a fuse or something added?).
Click to expand...
Easy enough, but there's a little bit more to it than that.

Their is a site that sells pre modded cables.
Click to expand...
There is, but I am personally very dubious about the wiring scheme he's chosen to supply the standby power (to the +28V pin)

You can read about my successful adventure here.

Short version:

  • Use an ATX power extender cable for your rewiring, so you can swap in another ATX PS whenever you like.
  • Spend $10 on the tool to remove the pins from the Molex connector, because it's a PITA otherwise.
  • +5VSB (standby) from the ATX PS works fine on the +28V pin, at least on my machine, but you won't be able to use powered Firewire devices without a powered hub, nor ADC monitors.
  • If that doesn't work, a Powerbook power supply (+24V) is worth a shot.


Best of luck and please do let us know how you progress :)

 
Well today was "crack open PSUs and fish about inside" day. The Gigabit Ethernet PSU showed nothing on a voltmeter so that proved the PSU was definitely shot. On closer inspection there's evidence of some blown part on the circuit board. Just not sure what it is yet.

The MDD one had a clearly blown thermistor. From what I've been reading on pages like this one this was probably what was causing the fuse to blow. We tried replacing it with a similar-looking one from a spare PC PSU but while it didn't pop like before, it did still blow the fuse in the plug. After some googling around and finding a picture of the actual part (it had blown where the part number was marked), the rating on the one we put in was different (5ohm/7A vs 4ohm/8A on the original).

So I'm a little wiser but still have two dead G4s. I'll take another look at the PSUs and see if I can identify the parts that need replacing (there's a few threads about these on badcaps and a post in one suggests that the same parts tended to fail on all these Samsung ones) and have a crack at getting them going.

 
Just checking: you do know you have to short standby to ground to get the PS to spark up, yeah?

 
Just checking: you do know you have to short standby to ground to get the PS to spark up, yeah?
Click to expand...
You mean for the Gigabit Ethernet one? I followed the instructions on the Apple support site.

Hmm actually I didn't follow them right. I didn't have it connected to the logic board.

 
Just checking: you do know you have to short standby to ground to get the PS to spark up, yeah?
Click to expand...
Now I understand what you meant. I didn't know you could do that to test if a PSU is working. Handy tip for the future!

Alas, the GE one is well and truly dead. And the MDD would involve quite a bit of dismantling and cap replacing to get working. Honestly considering how little the machines are worth it's hard to justify putting any money into repairing or replacing the PSUs so I think I'll just put them on the back shelf for the time being.

 
Well, using an ATX PSU and modding an extension cable is a decent investment because you can just remove the ATX PSUs and stick them in other PCs or modify other extensions for use with other Mac motherboards and such. Even could turn one into a bench power supply if needed.

A $50 Seasonic or Corsair would be able to handle anything those G4s can suck up as well as power a mild modern PC. Seasonic and Corsair are good brands too.

 
Hmm I have some ATX PSUs lying around. What was putting me off was adding the +28v needed for the GE. Having said that, I could live without powered firewire and I don't have an ADC monitor so I wonder if Bunsen's tip about wiring the +5VSB line into the +28V pin would work. Using a wall adapter to supply the +28V sounded like a messy solution.

I pulled out two of the PSUs I have. Both are 300W which is lower than the 338W the original AcBel one had. The first one has both power connectors on the back, while the other only has one and an on/off switch. This makes the first one a better fit but it has a lower amp rating on the +5VSB (1.5a vs 2a on the second PSU). Would that make the second one a better candidate for the +28V re-wiring job? Or are both out of the pciture because they're lower power than the the original.

 
so I wonder if Bunsen's tip about wiring the +5VSB line into the +28V pin would work
Click to expand...
It does work and I used to do it like that but I feel better using closer to the expected voltage and amperage. I have a 20v 4.5A dell laptop power adapter hooked up to my G4. Never had an issue with this adapter, though, it means my G4 now takes three electrical sockets including the display instead of just the previous two. I *should* get a nicely sized piece of wire and some connectors and set it up so I only need one socket but it is just not that big of a deal to me right now.

 
Hmm I have some ATX PSUs lying around. What was putting me off was adding the +28v needed for the GE. Having said that, I could live without powered firewire and I don't have an ADC monitor so I wonder if Bunsen's tip about wiring the +5VSB line into the +28V pin would work. Using a wall adapter to supply the +28V sounded like a messy solution.
I pulled out two of the PSUs I have. Both are 300W which is lower than the 338W the original AcBel one had. The first one has both power connectors on the back, while the other only has one and an on/off switch. This makes the first one a better fit but it has a lower amp rating on the +5VSB (1.5a vs 2a on the second PSU). Would that make the second one a better candidate for the +28V re-wiring job? Or are both out of the pciture because they're lower power than the the original.
Click to expand...
If you're feeling energetic, you can build this:

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

Note, that the contents of that file are not my work. You won't get enough 28V amps to drive an ADC monitor, but it will be enough for Firewire devices.

Since I found that file I've looked into "Boost" and "Buck-Boost" regulators at length (for aquarium LED lighting). There are a bunch of other choices besides the LM2577, but that one is already spec'ed out and seems good enough.

I don't know if it is still true, but in the distant past, the 5V-SB would tie to the regular 5V supply after the power supply activated. You could also do this with a rectifier and a current limiting resistor, so that the 5V can supply the 5V-SB but the 5V-SB will not supply the 5V If this is the case, then the current limit on the SB doesn't matter much, as there won't be much draw unless the computer is turned on. Of course, one will still be limited by the capacity of the boost circuit which is probably well under 1A total.

 
Hi trag

I actually have that file on my desktop! Downloaded it from somewhere during the week while researching all this. I don't know the first thing about electrics so can you tell me if the amp rating on the +5VSB would make any difference if I used it in place of the +28V as Bunsen did? In other words would there be any difference in using a PSU with 1.5A on the +5VSB as opposed to one with 2A? The original PSU had 4.04A on the +28V line.

 
the PSUs I have. Both are 300W which is lower than the 338W the original AcBel one had.
Click to expand...
Consider this: the original one had to provide enough power for the computer and a possible ADC monitor. I think you'd be fine with just the computer on 300W

The original PSU had 4.04A on the +28V line.
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Again, and I'm sure someone will correct me if I'm wrong, but that (>112W) allows for an ADC monitor. I think you'll be fine

 
I did a little more digging around and found a 20-pin 400w PSU and an 22-pin atx extension cable! So looks like I'm good to go. Just need to find a way to swap these wires with no proper tools :)

 
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