DIY Computers


DIY Computer Repairs   Post Beep Codes   Using a Postcard    Boot Diagnostic Flowchart

POST Card


Power on self test diagnostic card or POST cardThe Power On Self Test Diagnostic card or POST card is a handy little card used to diagnose faults with a computer if it fails to boot successfully. The POST card is usually a PCI expansion card inserted into a spare PCI slot. When a computer first starts up it executes a series of self tests and then broadcasts the results of these tests to an address on the mainboards bus that is readable from the PCI slot. The card displays the code of the last test that passed. BIOS manufacturers publish and periodically update the test codes and the order that they are performed so that we may then be able to interpret the result displayed by a POST card. Simply insert the POST card into a PCI slot and then switch the computer on, the codes displayed on the card will change as each self test the mainboard performs is executed and passed. Within a few seconds the code will stop changing and settle on a particular one. Now this is usually the code of the last test that passed successfully.

POST Code displayedThe picture to the right shows a POST card that has been inserted into one of our old test machines. When you use a POST card it is important to know what manufacturer made your motherboards BIOS, there are several different BIOS makers including Phoenix, Award and AMI (American Megatrends). You may need to visit your motherboard manufacturers website and look at the specifications of the board to determine the appropriate manufacturer. If you are lucky like we were in this instance you will find the BIOS chip on the motherboard has the manufacturers name on it. Our board uses AMI bios. The code displayed here is D3. When we look up AMI's test code listing we find D3, the last test it passed is described as "DMA Controler #1 #2 interupt Controller #1 #2 disabled. Chipset init/Auto memory detection about to begin" and this already contains a hint of what is wrong. The actual test it did not pass is D4 which is described as "Chipset initialization/Auto memory detection over, preparing to uncompress the RUNTIME code". If you guessed that it was a memory failure you were quite correct, we had removed the memory module from the machine entirely for the purpose of demonstrating the POST card.

So the advantages of owning a POST card are demonstrated quite ably in the above example and if you forsee yourself repairing a lot of computers the the trivial investment of purchasing such a card will soon pay for itself in time saved and more successfull diagnosis performed. Consider getting a POST card.




DIY Computer Repairs   Post Beep Codes   Using a Postcard    Boot Diagnostic Flowchart