PC: How to test a motherboard and power it without a case or power switch

Date: 2013

Problem:

When testing several motherboard back and forth with the same power supply or several different power supplies,  it can be tedious and time consuming. Especially if one were to remove and install the motherboard each time from the computer case. Here I share some tips on making the troubleshooting quicker and easier.

Solution:

There are dedicated ATX power supply tester you can purchase and it will be the quickest way to tell if all the necessary voltages are present and if the power supply is good.

To test the motherboard, especially if you have to test different configurations or different motherboard, it is not necessary to keep the motherboard in the computer case. You can put it on a non-conductive surface such as a desk, or a piece of plastic, as long as the solder joints on the bottm do not touch any metal part to short themselves out.

Normally, when the motherboard is inside the case, you press the power button, and the power button connected to a jumper (two pins) will create a closed circuit, this will send a low voltage signal to the SCR (Silicon Control Rectifier or thyristor) to power on the computer. Most of the computers since the 2000 use a temporary closed circuit at the power-on jumper to start the computer. That means, unlikely the old mechnical method of having a hard switch that holds the on and off position, the action of pressing a button is instead a triggering action to the SCR (thyristor) which latches in the "on" state and starts the computer. When turning off the computer, normally when the motherboard is in a case, by holding the power button for few seconds the computer will shut off. This has the effect of essentially shorting the power jumper for few seconds.

This means, as long as you know where is the power-on jump connected to the wires from the power button, you can keep the motherboard outside the case for testing. Take any good conductor and briefly touch the jumper, that will power on the computer. When shutting down, just touch the jumper for few seconds until the it powers off.

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