Editing Atari 600XL Troubleshooting Guide (section)

== Known Issues ==

=== 16 KB RAM Limitation ===
The most significant issue with the 600XL is its base 16 KB RAM. Many Atari 8-bit programs require 48 KB or 64 KB to run. Symptoms include:
* '''Programs fail to load from disk or cassette''' — they may start loading but crash immediately or report an "Error 2" (insufficient memory).
* '''BASIC programs that work on an 800XL crash on the 600XL''' — the BASIC interpreter reports "ERROR-2" (out of memory).
* '''Games display a blank screen after loading''' — the game initialises but cannot allocate sufficient memory for graphics and game data.

'''Resolution:''' Upgrade the RAM to 64 KB using the Atari 1064 module or an internal modification (see [[Atari 600XL General Maintenance#RAM Expansion Care]]).

=== CD4051 Multiplexer Failure (Keyboard) ===
The CD4051 analogue multiplexers at U22 and U23 are the most common point of failure for the keyboard. Symptoms range from individual dead keys to a completely non-functional keyboard. These are standard CMOS ICs and readily available as replacements (CD4051BE or CD4051BCN).

=== 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.

=== Oxidised IC Sockets ===
The factory-fitted single-wipe IC sockets are a known reliability issue on XL-series computers. Over time, oxidation builds up on the contact surfaces, causing intermittent failures. Symptoms include:
* Random crashes or lockups
* Failure to boot on some attempts
* Garbled graphics or missing colours

'''Resolution:''' Remove all socketed ICs, clean contacts with IPA, and preferably replace the sockets with machine-pin (dual-wipe) types.