The power ON button is connected to the motherboard with a blue/white twisted pair. The mother board has no power, and the power unit is turned OFF. How does/can operating the Power pushbutton turn on the Power Supply?
Catch 22?
John Hewitt, Malaga, Spain
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Because the power supply is never really completely off, but supplies standby power to the motherboard.
Through a logic switching ic.
Or are you saying although the power switch is off at the back of the supply you can still power up the pc via the front case ON button? If so then it shouldn't be possible.
Not when the 240v switch on power supply itself is in the off position.
Because the button is connected to the power supply via the motherboard. The power supply is always in standby unless you hit turn off the incoming mains.
MBQ
You don't need (electrical) power to turn power on - just the means of making a connection.
There is a permanent 5v line going to the motherboard which is used to power a circuit that monitors the push button. When the button is pressed it sends a signal to the psu that tells it to power up completely.
sponix
John Hewitt, Malaga, Spain
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Is the PSU switched on? Some have a little switch on the back panel.
Not usually fused IME. If you are sure the PSU is on (some have a physical mains input switch on the back), check the power switch is working correctly (should be a push to make switch). If that is OK (or even if not) you ought to be able to get the board to power up by shorting the power on pins on the MB. Note some boards require a working processor to be fitted before they will power up.
If that does not work then you either have a dead PSU or motherboard. You can test the PSU by disconnecting the MB connector (leave a CD ROM drive or something connected because this type of PSU will not run without any load) and use a small wire to short the green wire on the ATX connector to one of the adjacent black ones. That should cause the PSU to come on. If it does not then replace the PSU, if it does then replace the motherboard.
John Hewitt, Malaga, Spain
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Faulty PTS(push to make switch)
SNIP
Not seen previous posts, but my pSU fired up similarly but pc not, replaced cmos battery -------- all fine now!
PC power supplies are notoriously unreliable - they are usually the first thing that goes. However at =A320 to =A330 even from Maplin that's a tolerable replacement.
Rob
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