Apple Mac Pro A1186 Power Issue

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Just bought a used Apple Mac Pro A1186. When I plug in the power cable, the power automatically comes on w/o pushing the power button. If I leave the power cable plugged up it starts up/shuts down fine. Have tried SMC reset. Don't have Apple OS yet (using Ubuntu for testing). Otherwise the computer seems to work fine. Any thoughts please? Thanks in advance.
 

pigoo3

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Further info

I noticed that the power supply makes a "clicking" sound when the power cord is plugged in and unplugged. I suspect that this is a relay. I took the (4) power supply outputs loose and the problem went away when I left the bottom most connector loose. I then traced that out to a connector on the MB under the DIMM slots. When I leave that connector loose the power supply does not click when the plug is inserted. I pressed the diagnostic button on the MB and the "trickle" LED is fine (orange) and the "Power" LED is fine (green). Must be a problem with the MB itself.
 

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I noticed that the power supply makes a "clicking" sound when the power cord is plugged in and unplugged. I suspect that this is a relay.

I think that the clicking sound is normal when it is unplugged & plugged in. If the clicking continued without unplugging…then I would suspect the power supply.

The computer should not power on when plugging in the power cord (without pushing the power button). Again…it could be something to do with the power button. This is the obvious first thing to check.:)

- Nick
 
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Problem went away after installing Snow Leopard OS (disabled option for "startup automatically after a power failure"). Last user before me probably had that checked and it wrote it to BIOS. Thanks to all who responded and tried to help.
 
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That is good however you will learn there are no BIOS in any Mac, just EFI.
 

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