Editing Atari 800XL Troubleshooting Guide (section)

=== Keyboard & Joystick Issues ===
* Keyboard matrix faults: check for stuck or dead keys, clean the mylar membrane and connector.
* Joystick not detected: test continuity from port to POKEY (U24) and check for broken traces or bad solder joints.
* SIO (serial) port not working: inspect U25 (6520 PIA), SIO connector, and related circuitry.

{| class="wikitable styled-table"
! Symptom !! Probable Cause !! Action
|-
| No sound at all || Bad POKEY (U24), speaker, or amp || Replace U24; test speaker; check amp circuit
|-
| Some keys/joysticks dead || Bad keyboard mylar, POKEY, or traces || Clean/replace mylar; test/replace U24; repair traces
|-
| SIO not working || Bad PIA (U25), SIO connector || Replace U25; reflow connector
|}