What is a Diagnostic Card?

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  • Written By: Dulce Corazon
  • Edited By: W. Everett
  • Last Modified Date: 04 October 2019
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In computing, diagnostic tools are often needed for troubleshooting, especially when there is a problem with the computer hardware. One of these tools is called the diagnostic card, which is also referred to as power on self test (POST) diagnostic card. It is usually inserted into one of the computer's peripheral component interconnect (PCI) slots in order to start the diagnostics. With its installed diagnostic firmware the card will test the computer's various systems to find out where it went wrong. It basically checks the computer hardware for errors or symptoms of serious hardware problems by investigating the error codes produced by the basic input output system (BIOS).

A BIOS is pre-installed software in the motherboard of computers. It usually starts up even before the installed operating system begins to load. This system keeps the computer hardware in check, making sure that everything is running smoothly on the hardware side. The BIOS is the software being accessed by a diagnostic card so it can run tests on the hardware. They interface with each other to check problems with the computer's memory, central processing unit (CPU), display card and other key hardware components.


In computer repair, a diagnostic card can be extremely helpful in determining the problem, especially if there is no display on the computer monitor or if the computer has completely frozen. When a machine hangs and fails to restart or boot up again, the best chance of pinpointing the problem is by checking the hardware. A diagnostic card is often the key in determining where everything went wrong and, in effect, tells which direction to go in fixing the issue.

The diagnostic card works by detecting and reporting error codes generated by the motherboard. These codes are called beep codes. A motherboard needs to have a working BIOS and CPU in order for it to communicate with diagnostic utilities. This diagnostic card will be useless if a computer's motherboard is already fried. If it's still working, diagnostics can still be performed even without a computer monitor attached to the system. Using a speaker, the reported errors can be heard through audible beeps.

Diagnostic cards are specifically designed to discover and report errors found in the motherboard of a computer. This means it will not be able to detect problems in devices being plugged into the computer's slots and ports like the external hard drives, monitors, keyboards, mouse, and speakers. Not all manufacturers use the same set of beep codes on their hardware products so it is often recommended that one chooses a compatible diagnostic tool before using it on his computer.


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