Editing IBM 5100 Troubleshooting Guide (section)

== CRT Faults ==

* '''No raster''' — flyback failure; check for HV at anode (using HV probe only). No HV → flyback or horizontal output transistor failed.
* '''Raster but no characters''' — video timing chain (vertical scan generation from PALM).
* '''Dim raster''' — cathode emission loss; CRT is end-of-life.
* '''Single horizontal line''' — vertical deflection failure.
* '''Single vertical line''' — horizontal deflection failure (rare; usually accompanied by flyback failure).
* '''Bright single spot''' — both deflections failed; '''immediately power off''' to avoid burning the phosphor.