The 14‑inch Cincinnati Inc 840891/26S14MA503 is an industrial HMI monitor originally using a CRT display; it has been widely retrofitted with LCD upgrade kits (KME or LL series) to replace the aging cathode‑ray tube. Common failure modes for this unit include power supply degradation (especially the high‑voltage CRT driver), backlight and phosphor decay, loose or corroded front‑panel connectors, and display flicker or ghosting when the CRT is still in use; LCD conversions typically fail at the cable interface or in the new LCD controller board. First‑check diagnostics: verify 12 V/5 V supply rails with a multimeter, inspect all front‑panel connector pins for continuity and corrosion, and review any diagnostic codes or error logs from the host CNC controller that may indicate HMI communication faults.[oss-gpt-20b]