Editing Atari 600XL General Maintenance (section)

=== Common Keyboard Issues ===
* '''Dead keys''' — Often caused by dirty or oxidised membrane contacts. Clean with IPA and a cotton bud.
* '''Entire keyboard unresponsive''' — Check the CD4051 multiplexer ICs at positions U22 and U23. These are the most common cause of total keyboard failure on the 600XL. Replacement CD4051BE or CD4051BCN ICs are readily available and inexpensive.
* '''Intermittent key presses''' — May indicate degraded rubber domes or a poor connection between the membrane layers. Contact cleaner spray (e.g., DeoxIT D5) applied sparingly between the membrane layers can help.