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When a computer system fails to boot and a quick solution is needed there is no substitute for a motherboard diagnostic card, or POST card, for troubleshooting. These small boards plug into an available PCI slot on the motherboard while the power is off, and display a series of codes when the power is applied which indicate each step in the power on self-test (POST) process. When the system hangs, the corresponding code is read from the POST card and compared to the manual or an online reference to determine which component is most likely to have caused the failure.
To use a motherboard diagnostic card simply power down the computer and unplug the power cord from the back of the power supply. Allow the machine to sit until the small LED on the motherboard goes off, indicating that the power has drained from the system and it is safe to install the card. Attach an anti-static wrist strap to the case and to one arm. Slide the card into any available PCI slot, securing it into place with a single screw if the card has a hanger bracket attached. Connect the power cord and power on the system.
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Read the Code
When the computer turns on and attempts to boot, the diagnostic card will provide a readout indicating each hardware function that is being attempted by the motherboard. The last displayed code will indicate the problem when cross referenced with the documentation that came with the motherboard diagnostic card, or occasionally by using an online reference of diagnostic POST codes. No two cards are exactly the same, and no two motherboards give exactly the same readout, so it is important to find the codes that match the individual POST card and the system that is being tested.
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Solve the Problem
The goal of using a hardware diagnostic card is to solve the problem that is preventing the system from booting. This is generally done by swapping out components until the system works again, starting with the component indicated as a problem from the POST code displayed by the card.
If the RAM is indicated as a problem, for instance, power down the system and disconnect the power and then wait until the LED light goes out on the motherboard. Using an anti-static wrist strap as outlined above, remove the RAM and replace it with known-good modules. Reconnect the power, and turn the system back on to see if it boots normally.
If the system boots normally, then the problem is solved. If it does not boot, check the code on the diagnostic card to see if it stopped in a different place this time, indicating another problem. Swap the additional component with a known-good replacement and try again, leaving the replacement RAM in place. Repeat this process as necessary until the system boots, and then begin removing replacement parts starting with the first component that was replaced until just one replacement component is left in the system and it still boots normally.
Photo by Norm Dickinson