Editing Atari ST Troubleshooting Guide (section)

=== Display Corruption ===

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! Symptom !! Possible Cause !! Recommended Action
|-
| Vertical or horizontal bars/stripes || Shifter failure; bad connection between Shifter and data bus; failing RAM affecting video memory area || Reseat Shifter chip. Check Shifter retaining clips for adequate tension. If problem persists, try known-good Shifter from donor board.
|-
| Wrong or garbled colours || Shifter output fault; bad solder joint on RGB output path; monitor cable fault || Check 13-pin DIN cable for continuity on R, G, B pins (6, 7, 10). Check monitor connector for bent pins. Reseat Shifter.
|-
| Screen jitter or rolling || Sync signal fault; HSync or VSync not being generated correctly by GLUE || Check HSync (pin 9) and VSync (pin 12) on monitor port with oscilloscope. If absent, suspect GLUE chip. Check 32 MHz crystal.
|-
| Ghosting or wavy lines || PSU ripple; poor grounding; RF interference from internal PSU (1040ST) || Recap PSU. Check ground connections.
|-
| "Jail bars" (thin vertical lines on solid colours) || Impedance issues on the video output path; common on STFM boards || Sometimes improved by replacing decoupling capacitors near the Shifter. A known characteristic of the ST video circuit rather than a definitive fault.
|}