Atari 400 Troubleshooting Guide: Difference between revisions

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[[File:Atari 400 (photo).jpg|thumb|right|300px|Atari 400. Source: Wikimedia Commons.]]

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The Atari 400 does not display error codes or beep patterns.

For advanced diagnostics, use a test cartridge (e.g., Atari Diagnostic or SALT) if available.

== Diagnostic order and the Star Raiders test ==

On the Atari 8-bit machines the components fail, statistically, in this order: '''RAM → OS ROM → POKEY → GTIA/ANTIC → CPU'''. Work through them in that order. The '''Star Raiders''' cartridge is a quick diagnostic: it exercises ANTIC, the CPU and GTIA/CTIA, so if it runs those three are good and the fault is narrowed to the PIA, the OS ROM, the MMU or the RAM. Before swapping chips, leave the machine powered for about ten minutes and feel for an overheating RAM chip, and make sure the RAM, OS ROM, ANTIC, MMU, PIA and CPU are all fully seated (reseating cures many garbage-screen / no-boot faults).<ref name="atari8">[https://8bithardware.wixsite.com/website/post/atari-8-bit-400-800-xl-xl-pictorial-fault-guide Atari 8-bit pictorial fault guide], 8bithardware; [https://atari-owner.com/club/articles/black-screen-problems-xl-xe-fix-checklist.25/ Black Screen [XL/XE] Fix Checklist], Atari Owners Club; and AtariAge repair threads. Source for the RAM→ROM→POKEY→GTIA/ANTIC→CPU failure order, the Star Raiders diagnostic cartridge, the seated-socket checks, the PSU 470 uF capacitor and switch/connector faults, and the SALLY 1.79 MHz clock/reset checks.</ref>

== Power and clock ==

* '''Power''': the external "ingot" supply, an oxidised power switch and a cracked DC power connector all cause dead or intermittent operation. Check the switch and connector, and test/replace the '''470 uF 16 V''' radial electrolytic in the left-rear corner of the board.<ref name="atari8">[https://8bithardware.wixsite.com/website/post/atari-8-bit-400-800-xl-xl-pictorial-fault-guide Atari 8-bit pictorial fault guide], 8bithardware; [https://atari-owner.com/club/articles/black-screen-problems-xl-xe-fix-checklist.25/ Black Screen [XL/XE] Fix Checklist], Atari Owners Club; and AtariAge repair threads. Source for the RAM→ROM→POKEY→GTIA/ANTIC→CPU failure order, the Star Raiders diagnostic cartridge, the seated-socket checks, the PSU 470 uF capacitor and switch/connector faults, and the SALLY 1.79 MHz clock/reset checks.</ref>

* '''CPU clock and reset''': check for a clean '''1.79 MHz''' clock at the 6502/SALLY (pin 37), and that RESET pulses low then high at power-up. A RESET stuck low points to the reset circuit.<ref name="atari8">[https://8bithardware.wixsite.com/website/post/atari-8-bit-400-800-xl-xl-pictorial-fault-guide Atari 8-bit pictorial fault guide], 8bithardware; [https://atari-owner.com/club/articles/black-screen-problems-xl-xe-fix-checklist.25/ Black Screen [XL/XE] Fix Checklist], Atari Owners Club; and AtariAge repair threads. Source for the RAM→ROM→POKEY→GTIA/ANTIC→CPU failure order, the Star Raiders diagnostic cartridge, the seated-socket checks, the PSU 470 uF capacitor and switch/connector faults, and the SALLY 1.79 MHz clock/reset checks.</ref>

== Keyboard and POKEY ==

POKEY scans the keyboard and generates the sound and the SIO serial signals. '''A dead keyboard while sound still works''' is a classic POKEY (or keyboard-membrane) fault; SIO/peripheral problems also point to POKEY.<ref name="atari8">[https://8bithardware.wixsite.com/website/post/atari-8-bit-400-800-xl-xl-pictorial-fault-guide Atari 8-bit pictorial fault guide], 8bithardware; [https://atari-owner.com/club/articles/black-screen-problems-xl-xe-fix-checklist.25/ Black Screen [XL/XE] Fix Checklist], Atari Owners Club; and AtariAge repair threads. Source for the RAM→ROM→POKEY→GTIA/ANTIC→CPU failure order, the Star Raiders diagnostic cartridge, the seated-socket checks, the PSU 470 uF capacitor and switch/connector faults, and the SALLY 1.79 MHz clock/reset checks.</ref>

== References ==

== Related Pages ==

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+[[File:Atari 400 (photo).jpg|thumb|right|300px|Atari 400. Source: Wikimedia Commons.]]
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 The Atari 400 does not display error codes or beep patterns.
 For advanced diagnostics, use a test cartridge (e.g., Atari Diagnostic or SALT) if available.
+== Diagnostic order and the Star Raiders test ==
+On the Atari 8-bit machines the components fail, statistically, in this order: '''RAM → OS ROM → POKEY → GTIA/ANTIC → CPU'''. Work through them in that order. The '''Star Raiders''' cartridge is a quick diagnostic: it exercises ANTIC, the CPU and GTIA/CTIA, so if it runs those three are good and the fault is narrowed to the PIA, the OS ROM, the MMU or the RAM. Before swapping chips, leave the machine powered for about ten minutes and feel for an overheating RAM chip, and make sure the RAM, OS ROM, ANTIC, MMU, PIA and CPU are all fully seated (reseating cures many garbage-screen / no-boot faults).<ref name="atari8">[https://8bithardware.wixsite.com/website/post/atari-8-bit-400-800-xl-xl-pictorial-fault-guide Atari 8-bit pictorial fault guide], 8bithardware; [https://atari-owner.com/club/articles/black-screen-problems-xl-xe-fix-checklist.25/ Black Screen [XL/XE] Fix Checklist], Atari Owners Club; and AtariAge repair threads. Source for the RAM→ROM→POKEY→GTIA/ANTIC→CPU failure order, the Star Raiders diagnostic cartridge, the seated-socket checks, the PSU 470 uF capacitor and switch/connector faults, and the SALLY 1.79 MHz clock/reset checks.</ref>
+== Power and clock ==
+* '''Power''': the external "ingot" supply, an oxidised power switch and a cracked DC power connector all cause dead or intermittent operation. Check the switch and connector, and test/replace the '''470 uF 16 V''' radial electrolytic in the left-rear corner of the board.<ref name="atari8">[https://8bithardware.wixsite.com/website/post/atari-8-bit-400-800-xl-xl-pictorial-fault-guide Atari 8-bit pictorial fault guide], 8bithardware; [https://atari-owner.com/club/articles/black-screen-problems-xl-xe-fix-checklist.25/ Black Screen [XL/XE] Fix Checklist], Atari Owners Club; and AtariAge repair threads. Source for the RAM→ROM→POKEY→GTIA/ANTIC→CPU failure order, the Star Raiders diagnostic cartridge, the seated-socket checks, the PSU 470 uF capacitor and switch/connector faults, and the SALLY 1.79 MHz clock/reset checks.</ref>
+* '''CPU clock and reset''': check for a clean '''1.79 MHz''' clock at the 6502/SALLY (pin 37), and that RESET pulses low then high at power-up. A RESET stuck low points to the reset circuit.<ref name="atari8">[https://8bithardware.wixsite.com/website/post/atari-8-bit-400-800-xl-xl-pictorial-fault-guide Atari 8-bit pictorial fault guide], 8bithardware; [https://atari-owner.com/club/articles/black-screen-problems-xl-xe-fix-checklist.25/ Black Screen [XL/XE] Fix Checklist], Atari Owners Club; and AtariAge repair threads. Source for the RAM→ROM→POKEY→GTIA/ANTIC→CPU failure order, the Star Raiders diagnostic cartridge, the seated-socket checks, the PSU 470 uF capacitor and switch/connector faults, and the SALLY 1.79 MHz clock/reset checks.</ref>
+== Keyboard and POKEY ==
+POKEY scans the keyboard and generates the sound and the SIO serial signals. '''A dead keyboard while sound still works''' is a classic POKEY (or keyboard-membrane) fault; SIO/peripheral problems also point to POKEY.<ref name="atari8">[https://8bithardware.wixsite.com/website/post/atari-8-bit-400-800-xl-xl-pictorial-fault-guide Atari 8-bit pictorial fault guide], 8bithardware; [https://atari-owner.com/club/articles/black-screen-problems-xl-xe-fix-checklist.25/ Black Screen [XL/XE] Fix Checklist], Atari Owners Club; and AtariAge repair threads. Source for the RAM→ROM→POKEY→GTIA/ANTIC→CPU failure order, the Star Raiders diagnostic cartridge, the seated-socket checks, the PSU 470 uF capacitor and switch/connector faults, and the SALLY 1.79 MHz clock/reset checks.</ref>
+== References ==
+<references />
 == Related Pages ==