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POST Tasks and Beep Codes
When you turn on or reset an IBM- compatible PC, the BIOS first performs a number of tasks, called the Power- On- Self- Test (POST). These tasks test and initialize the hardware and then boot the Operating System from the hard disk.

At the beginning of each POST task, the BIOS outputs the test- point error code to I/ O port 80h. Programmers and technicians use this code during trouble shooting to establish at what point the system failed and what routine was being performed. Some motherboards are equipped with a seven- segment LED display that displays the current value of port 80h. For production boards which do not contain the LED display, you can purchase an installable "Port 80h" card that performs the same function. If the BIOS detects a terminal error condition, it issues a terminal- error beep code (See following), attempts to display the error code on upper left corner of the screen and on the port 80h LED display, and halts POST. It attempts repeatedly to write the error to the screen. This attempt may "hash" some CGA displays. If the system hangs before the BIOS can process the error, the value displayed at the port 80h is the last test performed. In this case, the screen does not display the error code.

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Terminal POST Errors
There are several POST routines that require success to finish POST. If they fail, they issue a POST Terminal Error and shut down the system. Before shutting down the system, the error handler issues a beep code signifying the test point error, writes the error to port 80h, attempts to initialize the video, and writes the error in the upper left corner of the screen (using both mono and color adapters).

Except for beep code #8, these codes are always fatal.

· 1 beep Refresh failure
· 2 beeps Parity error
· 3 beeps Base 64K memory failure
· 4 beeps Timer not operational
· 5 beeps Processor error
· 6 beeps 8042 - gate A20 failure
· 7 beeps Processor exception interrupt error
· 8 beeps Display memory read/write failure
· 9 beeps ROM checksum error
· 10 beeps CMOS shutdown register read/write error
· 11 beeps Cache memory bad

· For 1 beep, 2 beeps, or 3 beeps try reseating the memory first. If the error still occurs, replace the memory with known good chips.

· For 4 beeps, 5 beeps, 7 beeps, or 10 beeps the system board must be sent in for repair.

· For 6 beeps try reseating the keyboard controller chip. If the error still occurs, replace the keyboard chip. If the error persists, check parts of the system relating to the keyboard, e.g. try another keyboard, check to see if the system has a keyboard fuse.

· 8 beeps indicate a memory error on the video adapter. Replace the video card or the memory on the video card.

· 9 beeps indicate faulty BIOS chip(s). It is not likely that this error can be corrected by reseating the chips. Consult the motherboard supplier or an AMI product distributor for replacement part(s).
· If no beeps are heard and no display is on the screen, The first thing to check is the power supply. Connect an LED to the POWER LED connection on the motherboard. If this LED lights and the drive(s) spin up then the power supply will usually be good.

· Next, inspect the motherboard for loose components. A loose or missing CPU, BIOS chip, Crystal Oscillator, or Chipset chip will cause the motherboard not to function.