A+ Hardware Service Technician: Upgrades, Troubleshooting and Preventative Maintenance

Previous Page - Next Page

POST

POST, or Power On Self Test is your first source of troubleshooting a problem. POST automatically runs when your computer is turned on and tests several components of your PC.

The Processor – if the test fails for the CPU, the system stops usually with no error code.

ROMs – POST checks the BIOS ROMs. If there is a problem, the system will stop, usually with no error code.

DMA Controller – if there are any problems with the DMA controller, the system will stop.

Interrupt Controller – if POST detects problems with the Interrupt Controller the system will give an audible error signal of one long beep then one short beep then the system stops.

System Timing Chip – this chip provides timing signals for the bus and processor. Any errors will produce an audible error signal of one long beep and one short beep then the system stops.

Video Card – if the Video Card fails, there will be one long beep then two short beeps then the system halts.

RAM – any RAM errors will generate a “201: Memory Error” message on the screen. Any error codes beginning with 2 indicate a memory error.

Keyboard – a problem with the keyboard will result in a “301: Keyboard Failure” error message followed by a short beep. System may halt or may ignore the error.

Floppy Drives – any problems will result in a “601: Floppy Disk” error code appearing on the screen.

Other Devices – POST checks the other ports and components of the computer, beeps, then continues. It also checks the Master Boot Record (MBR) on the hard drive. If it cannot find the MBR, it will freeze and not continue loading, otherwise it hands control over to the MBR (or DOS Boot Record (DBR) if it is booting from a floppy).

Summary of POST error codes:

Previous Page - Next Page