Editing Atari 600XL Troubleshooting Guide (section)

=== OS ROM Boot to Self-Test ===
If the system boots directly to the self-test screen without the OPTION key being held:
# '''Check the BASIC ROM''' at U3 — remove and reseat. If the issue persists, the ROM may have failed.
# '''Check the OS ROM''' at U2 — reseat in socket.
# '''Verify the OPTION key''' is not stuck or shorted — a stuck OPTION key contact in the membrane can trigger self-test on every boot.