Heat require current and *voltage*. If it is a short circuit, there will be no voltage across it, hence no heat.I tested for continuity on the 8-pin connector next to the cpu socket with the motherboard out of the case and nothing connected to it, without cpu and ram.
Wouldn't it be much easier just freezing the board, apply current and check where it melts first?
That's true for a constant current power supply, but what if I apply 12V to it with nothing but a current limiting resistor, where will all the power go to?Heat require current and *voltage*. If it is a short circuit, there will be no voltage across it, hence no heat.
Just as an example... If you take 12 volts and apply it through a resistor into a 'shorted' board, most of the voltage will drop across the resistor. Really no different than using a CC supply. So you may only have a volt or so on the board itself. Assume the short is on the far side of the board from where you are connecting power: There will be no heat generated at the short, because no voltage will be across the short -- or look at it as P = I²R, if r is zero, no power dissipated.That's true for a constant current power supply, but what if I apply 12V to it with nothing but a current limiting resistor, where will all the power go to?
Heat require current and *voltage*. If it is a short circuit, there will be no voltage across it, hence no heat.
Nah, I disagree.Just as an example... If you take 12 volts and apply it through a resistor into a 'shorted' board, most of the voltage will drop across the resistor. Really no different than using a CC supply. So you may only have a volt or so on the board itself. Assume the short is on the far side of the board from where you are connecting power: There will be no heat generated at the short, because no voltage will be across the short -- or look at it as P = I²R, if r is zero, no power dissipated.
The voltage will be dropped across the runs in the board between the source and the 'short'. The heat may be well distributed across the board. So you can't use location of heat to determine location of short.
But this is getting a bit off subject. Put some current into the board and follow the voltage drops with your voltmeter. You'll find the short.
I third LesJones use a meterI think I would try passing a current of between 100 mA and one amp between the +12 volt and ground inputs of the mother board. Then using a DC milivoltmeter measure the voltage between the terminals of components that you think are across the 12 volt rail and ground. the component with the lowest voltage reading is probably the one that is shorted. A mother board will have many layers so following the + 12 volts track will probably be difficult.
Les.
You'd need a 4 wire milliohm meter. A normal ohmmeter is not sensitive enough.You can use your ohmmeter to find where the resistance between 12V and gnd is the lowest. That is where you will most likely find your short. It's probably an electo cap somewhere. If the cap is internally shorted, there won't be any bulging.
Perhaps. Perhaps not.Any shorted component is likely to have higher resistance than PCB tracks, and heat up before they do.