Editing Atari 600XL Troubleshooting Guide (section)

=== Built-in Self-Test ===
The Atari 600XL includes a built-in self-test in ROM, accessible by holding the '''OPTION''' key during power-on. The self-test performs:
# '''RAM test''' — Tests all available RAM and reports errors by address.
# '''ROM checksum''' — Verifies the integrity of the OS and BASIC ROMs.
# '''POKEY audio test''' — Plays a sequence of tones through each channel.
# '''Keyboard test''' — Displays key presses on screen.

If the system boots directly to the self-test screen without holding OPTION, this typically indicates a '''ROM or BASIC failure''' — the OS cannot find a valid BASIC ROM and falls through to self-test.