motherboards

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I have 2 Dell motherboards 440bx, they both quit turning on the power supply, can i bypass anything to make them work or should i trash them..thanks.
 

~Candy~

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Hi, what do you mean when you say they "quit turning on the power supply?"

The power supply sends the power TO the motherboard, cpu, etc.
 

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From the case on/off switch you have a ribbon cable that plugs into the MB, somehow the MB switches on the power supply, that all i know..thanks, Sam
 
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The power is switched on by the momentary contact across two pins on the motherboard using the "On" switch. You should be able to test the board by locating the pins and briefly shorting them with something to see if the system powers up, if it works the board is fine and the switch is bad. You can also bypass the motherboard by jumping across two of the power supply leads which has the same effect and will power up the system.
 

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Hi, I have no schematic on a AT pwr supply, could you tell me what two leads i need to jumper, thanks a bunch...Sam
 
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The scenario I was talking about only works on ATX power supplies. The AT power supply is not controlled by the motherboard, it's controlled by the case switch.
 
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Not the power supply you should eb looking at. Look at the motherboard pins and find the ones for power on/off. Short thos 2 pins together and it should fire up. If it is a BX chipset it is more than likely an ATX power supply.
 

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Ok, i was wrong you guy's are right it is a ATX pwr supply, can you still tell me what leads to jumper on the pwr supply to turn it on...thanks
 

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With the MB i am using now everything is fine, i've tried shorting the pins on the other MB's the pwr supply will not turn on, do the pins marked pwr on the MB enable another chip on the board thats turns on the pwr supply, if so how ddo i by pass it.
 
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The pins in question send a signal to the power supply to turn on....through the MB. There is no logic between the switch and the power supply, it's integrated into the power supply. Plug the PS into the motherboard, disconnect the current switch from the motherboard and either find another momentary switch (radio shack) or just short the pwr pin and the ground pin together.
 
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