Test PSU PowerMac Quad G5

JEBMAC

macrumors newbie
Original poster
May 15, 2015
10
0
Hello... I have been searching the WEB for any indication how I can test the PSU of a G5 Quad ( 1000W ). I have found the one for Dual core where to link the green wire, etc but the Quad PSU is different. What I want to be able to do it try to Start up the PSU when it is out of the PC. The MAC is not running but there is trickle volts ( the amber light on the logic board comes on if the Plastic Air cover is removed. The Mac seem dead but the white light does come on if I push the On Button. I have tried all of the known test.. Reset the startup with the little button by the RAM, Change the 3volt battery, RAM check, Graphic card, etc. I did buy another PSU on Ebay but if made know difference to the symptoms so I am not sure if the replacement PSU does work ( it was listed as working )

There must be a way of forcing the PSU to output volts when it is out of the PC

Thanks in advance.. John
 

poiihy

macrumors 68020
Aug 22, 2014
2,285
52
Well on typical ATX PSUs you'd connect the green wire to black. Green wire would have 5v and you drain that to ground and it will turn on. But on my beige G3 power supply I was really puzzled. The green did not output any voltage. The only wire that outputted voltage was the purple 5v trickle charge. After some tinkering I found that you drain the 5v trickle charge to the green wire and it would turn on!

Test the voltage between green and black, and if there is nothing, then you probably turn it on by connecting purple to green.

If that doesn't work then try connecting purple (or whatever wire has the trickle charge) to each pin until it works.
 

JEBMAC

macrumors newbie
Original poster
May 15, 2015
10
0
Thanks for the reply. Unfortunately the MAC PSU is very different to the ATX type. So I will have to see if anyone on here know that actual PSU and a way to test it out of the MAC machine..
 

Sergey.P

macrumors newbie
Aug 27, 2013
15
0
Finland/Russia
If finding pinout for G5's PSU is such a tough task I would go by the easiest way:
Does PSU start when you push on the power button of your PM? Assuming it does and the goal of the whole procedure is to measure the output voltages of the PSU, just run the PM as it is and poke the multimeter's leads into the PSU's pins on the logic board.
If PSU doesn't start though, it's a different story.. IMHO the pinout of Quad's PSU should't be different from a regular DC.
 

JEBMAC

macrumors newbie
Original poster
May 15, 2015
10
0
Hi There. The Quad 1000 watt PSU is difference from the Dual core one. As I mentioned in the original question, it does not power up .. but the 5 volt trickle light comes on when I remove the clear fan cover and the white light above the power button comes on, but no fans or boot.

The only way to fault find it is to remove the PSU and then work out what the pin out from the Power button is to tell the PSU to fire up so I can measure for 12volts etc. I am not sure if there is a short on the main board shutting the PSU down.. I can find details of what volts should be on what pins but it does not show what the start up pin out connections are.
 

Sergey.P

macrumors newbie
Aug 27, 2013
15
0
Finland/Russia
Ok, but the circuit board of PSU has all the wires labeled on it, so just open up the PSU case and look up those labels for clue of PS_ON wire.
 

poiihy

macrumors 68020
Aug 22, 2014
2,285
52
Thanks for the reply. Unfortunately the MAC PSU is very different to the ATX type. So I will have to see if anyone on here know that actual PSU and a way to test it out of the MAC machine..
No, it is not "very different" it is actually similar. But I am talking about MAC Power supplies, not ATX.
Does your connector have a green wire? Test green to black and if there is 5v, connect green to black, but if there is not 5v, then try a different method. Does your connector have a purple wire? Test purple to black and if there is 5v, connect purple to green. Did it turn on?

I have a MAC power supply and it turns on by connecting purple to green. Purple is the 5v trickle, and green receives the 5v trickle.

----------

I can find details of what volts should be on what pins but it does not show what the start up pin out connections are.
If it has a green wire then it should be that wire. See if it outputs 5v or not. If it doesn't, it probably receives 5v from the trickle.
 

JEBMAC

macrumors newbie
Original poster
May 15, 2015
10
0
Anyone know which 2 pins of the Molex connector are need to be shorted together to start up the PSU
startup.jpg
 

DZ/015

macrumors 6502a
Mar 23, 2003
875
21
New England
I don't know what wires to short. But I looked through the service manual and it does not give this information either. According to the troubleshooting guide in the manual, you may have a failed logic board or processor(s). Here is the manual in case you do not have it.
 

JEBMAC

macrumors newbie
Original poster
May 15, 2015
10
0
Hello.. Thanks for the Manual. It is a better overview than I have so that's great. The problem I have is that there is trickle volts and if I push the ON button the white light shows... There are no fans or any other sign of life. I bought another Power supply and tried it but it has the same result. So I am not sure if the PSU I bought actually works...even though I was told it did, so I am trying to find a was to start up the PSU on the bench and not inside the MAC.. It is strange that it seems no one knows how to do this....Thanks again for you help Regards
 

Mnowell69

macrumors regular
Jul 4, 2013
246
36
Bedford, UK
have you read/tried the advice on pages 141, 142,143 of the manual. you can test the voltage from the 'tabs' below the processor
 

JEBMAC

macrumors newbie
Original poster
May 15, 2015
10
0
have you read/tried the advice on pages 141, 142,143 of the manual. you can test the voltage from the 'tabs' below the processor
have you read/tried the advice on pages 141, 142,143 of the manual. you can test the voltage from the 'tabs' below the processor
I am aware of all the output location but i want to see if the psu is working outside on a bench test
 

JEBMAC

macrumors newbie
Original poster
May 15, 2015
10
0
I did look at that option some time ago but my concern at the moment is to find out whether the PSUs I have actually have a problem. As one is buried inside the MAC it is difficult to do any tests, hence I want to be able to bench test it. There must be someone somewhere who knows how to test it outside of the MAC. ATX is easy.. I have an ATX PSU tester :)....
 

Mnowell69

macrumors regular
Jul 4, 2013
246
36
Bedford, UK
i thought all you would have to do is connect the green wire to a ground (psu case or gnd wire)and plug the psu in and it should fire up. The psu doesn't have to be in the computer. when my G5 arrives i'll give it a go if you haven't already. :)
 

JEBMAC

macrumors newbie
Original poster
May 15, 2015
10
0
Hi .... There is no green wire on the Molex connector. It is not obvious what is the correct one.. I don't want to just start shorting out each one to ground as it may make things worse....Remember the PSU is for the quad core 1000w version..
 

Mnowell69

macrumors regular
Jul 4, 2013
246
36
Bedford, UK
Hi .... There is no green wire on the Molex connector. It is not obvious what is the correct one.. I don't want to just start shorting out each one to ground as it may make things worse....Remember the PSU is for the quad core 1000w version..
Quite right. I have yet to see mine so i can only stab in the dark (so to speak)
 

JEBMAC

macrumors newbie
Original poster
May 15, 2015
10
0
Hi. I now have the picture of the connections

Does this help to identify the start-up wires?

Regards

John
 

Attachments

poiihy

macrumors 68020
Aug 22, 2014
2,285
52
Hi. I now have the picture of the connections

Does this help to identify the start-up wires?

Regards

John
Ok, so that PS_ON wire (the brown one? Can't quite see...) definitely has something to do with turning it on. You can use a wire and jump it to each other wire until you find one that works. Don't worry, nothing would break.
 

poiihy

macrumors 68020
Aug 22, 2014
2,285
52
Jump the ps-on pin to a ground pin. That should start the power supply, if it's good.
Yes, try that, but that won't necessarily start it. The power supplies from beige G3s used the green wire as the input... With typical ATX PSUs the green has 5v and when it is depleted (like when it is connected to ground) the PSU turns on. But with the beige G3 there is 0v at the green wire; instead you have to connect the 5v trickle wire (purple) to green. So I wouldn't be surprised if the green here outputs power or not.

You can test this with a volt meter by probing between green (or in this case, brown). and black and see if there is voltage. If not, then brown receives power instead of outputs it, and some other wire outputs power for green to receive. Test the voltage between each wire and ground and you will find a wire that outputs power, probably a 5v trickle charge. Connect this to the brown wire and see if it works.
 
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