Editing Osborne 1 Troubleshooting Guide (section)

== Display & Chime Diagnostics ==

The Osborne 1’s 5" CRT should display a raster and beep at startup. Display issues are often due to power, logic, or CRT subsystem faults.

=== No Video, No Raster ===
* Confirm CRT filament glows faintly (view in a dark room).
* Check for high voltage “static” on the CRT face.
* Inspect CRT board for burnt resistors, failed flyback transformer, or broken neck board.

=== Raster but No Text ===
* Indicates video section is working, but logic board is not sending video data.
* Reseat all socketed ICs, especially video RAM and character ROM.
* Check ribbon cable from logic board to CRT board for continuity.

=== Garbled or Rolling Display ===
* Suspect failed video RAM, character ROM, or timing logic (e.g. 74LS chips).
* Adjust vertical/horizontal hold pots if rolling; if ineffective, check timing ICs.

{| class="wikitable styled-table"
! Symptom !! Likely Cause !! Action
|-
| No raster, no CRT glow || CRT filament supply failure, flyback dead || Check/replace flyback; test filament voltage
|-
| Raster present, no text || Logic board not running, video cable loose || Reseat logic board, check video cable
|-
| Garbled/rolling text || Video RAM/ROM or timing logic faulty || Swap video RAM/ROM; check 74LS chips
|}