Editing Atari 1200XL Troubleshooting Guide (section)

=== ANTIC (U20, C012296) – Display Processor ===
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|+ '''ANTIC Fault Symptoms'''
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! Symptom !! Probable Cause !! Verification
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| No display (black screen) with +5V and clock present || ANTIC not generating display list || Check ANTIC NMI output (pin 7). Verify ANTIC has valid Ø2 clock on pin 29.
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| Garbled or corrupt text/graphics || ANTIC address bus fault || Probe ANTIC address outputs (pins 10–20, 22–24) for activity during display.
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| Memory self-test fails on all RAM || ANTIC refresh failure || ANTIC pin 8 (REF) should pulse during operation. If absent, ANTIC is not refreshing DRAM.
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| Screen rolls vertically || ANTIC VSYNC fault || Check ANTIC AN0–AN2 outputs (pins 2, 3, 5) to GTIA.
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