Atari 800XL Troubleshooting Guide: Difference between revisions
Expand troubleshooting: fail-order, Star Raiders diagnostic, PSU/clock/reset, POKEY keyboard, internal BASIC; cited (AtariAge/8bithardware) |
Deep dive: chip map (SALLY/ANTIC/GTIA/POKEY/PIA/MMU/FREDDIE), Star Raiders diagnostic, POKEY signatures, diagnostic order; cited |
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The XL/XE machines have BASIC built in. A bad internal BASIC ROM can stop the machine booting; '''hold OPTION at power-on to disable internal BASIC''' as a test (and to run software that needs BASIC off). If the machine boots with OPTION held but not without, suspect the BASIC ROM.<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> | The XL/XE machines have BASIC built in. A bad internal BASIC ROM can stop the machine booting; '''hold OPTION at power-on to disable internal BASIC''' as a test (and to run software that needs BASIC off). If the machine boots with OPTION held but not without, suspect the BASIC ROM.<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> | ||
== Component-level faults (deep dive) == | |||
=== Chip map === | |||
{| class="wikitable styled-table" | |||
! Chip !! Role | |||
|- | |||
| '''SALLY''' (6502C) || CPU (6502 with HALT for DMA) | |||
|- | |||
| '''ANTIC''' || Display-list / DMA processor | |||
|- | |||
| '''GTIA''' (CTIA on early boards) || Colour, playfield and player/missile graphics | |||
|- | |||
| '''POKEY''' || Keyboard scan, SIO serial, sound, paddles | |||
|- | |||
| '''PIA''' (6520) || Joystick ports and control lines | |||
|- | |||
| '''MMU''' || Memory management (OS / BASIC / RAM banking) | |||
|- | |||
| '''FREDDIE''' || DRAM controller (later 800XL / 65XE) | |||
|} | |||
=== Star Raiders diagnostic === | |||
The Star Raiders cartridge exercises '''ANTIC, the CPU and GTIA/CTIA''' (and needs the first 8 KB of RAM good). If it runs cleanly, those three chips and the low RAM are fine, which narrows a remaining fault to the '''PIA, OS ROM, MMU or RAM'''.<ref name="a8flt">[https://8bithardware.wixsite.com/website/post/atari-8-bit-400-800-xl-xl-pictorial-fault-guide Atari 8-bit (400/800/XL/XE) pictorial fault guide], 8bit-Hardware; [https://atariprojects.org/2025/01/01/label-the-6502-cpu-antic-gtia-pokey-and-pia-chips-for-easier-troubleshooting-using-a-multimeter-or-oscilloscope-10-15-mins/ Label the 6502 CPU, ANTIC, GTIA, POKEY and PIA Chips], Atari Projects; and [https://www.atarimania.com/pgefaq_chapitre.awp?id=14 What are SALLY, ANTIC, GTIA, POKEY and FREDDIE?], Atarimania. Source for the Star Raiders diagnostic coverage (ANTIC/CPU/GTIA), the POKEY fault signatures (keyboard vs SIO), the GTIA/ANTIC binary behaviour, and the reseat-first / RAM-and-socket-most-common guidance.</ref> | |||
=== POKEY fault signatures === | |||
POKEY fails in tell-tale ways: the keyboard is dead but sound still works; or keyboard and sound work but '''SIO''' does not — sometimes SIO fails only at divisor 0 (the fastest rate) yet works at divisor 4/6/8. '''GTIA and ANTIC are largely binary''' (working or dead); SALLY can show subtler faults.<ref name="a8flt">[https://8bithardware.wixsite.com/website/post/atari-8-bit-400-800-xl-xl-pictorial-fault-guide Atari 8-bit (400/800/XL/XE) pictorial fault guide], 8bit-Hardware; [https://atariprojects.org/2025/01/01/label-the-6502-cpu-antic-gtia-pokey-and-pia-chips-for-easier-troubleshooting-using-a-multimeter-or-oscilloscope-10-15-mins/ Label the 6502 CPU, ANTIC, GTIA, POKEY and PIA Chips], Atari Projects; and [https://www.atarimania.com/pgefaq_chapitre.awp?id=14 What are SALLY, ANTIC, GTIA, POKEY and FREDDIE?], Atarimania. Source for the Star Raiders diagnostic coverage (ANTIC/CPU/GTIA), the POKEY fault signatures (keyboard vs SIO), the GTIA/ANTIC binary behaviour, and the reseat-first / RAM-and-socket-most-common guidance.</ref> | |||
=== Diagnostic order === | |||
Reseat all socketed ICs first; statistically '''RAM and socket faults are the most common, then ROM, then POKEY'''. After POKEY and the PIA, check the 74158 multiplexers, the 08/137/375, the delay line and the MMU. Use piggy-back or substitution for RAM and logic, fit sockets for any replaced chip, and recap an ageing board. The built-in self-test (RAM, audio-visual and keyboard tests) is a quick first check on a machine that boots far enough to reach it.<ref name="a8flt">[https://8bithardware.wixsite.com/website/post/atari-8-bit-400-800-xl-xl-pictorial-fault-guide Atari 8-bit (400/800/XL/XE) pictorial fault guide], 8bit-Hardware; [https://atariprojects.org/2025/01/01/label-the-6502-cpu-antic-gtia-pokey-and-pia-chips-for-easier-troubleshooting-using-a-multimeter-or-oscilloscope-10-15-mins/ Label the 6502 CPU, ANTIC, GTIA, POKEY and PIA Chips], Atari Projects; and [https://www.atarimania.com/pgefaq_chapitre.awp?id=14 What are SALLY, ANTIC, GTIA, POKEY and FREDDIE?], Atarimania. Source for the Star Raiders diagnostic coverage (ANTIC/CPU/GTIA), the POKEY fault signatures (keyboard vs SIO), the GTIA/ANTIC binary behaviour, and the reseat-first / RAM-and-socket-most-common guidance.</ref> | |||
== References == | == References == | ||