Editing IBM 5120 Maintenance Guide (section)

== CRT Maintenance ==

The 9-inch CRT and its deflection / flyback board are mounted in the lower chassis on a sub-chassis:

* Always discharge the CRT anode before any work on the deflection board.
* Inspect the flyback transformer for cracked insulation — visible cracking indicates impending arc-over; flyback replacement requires a donor.
* Deflection coils — inspect for cracked solder joints at the yoke connector.
* Phosphor burn-in — if a static image is visible on the inactive screen, the phosphor has been operated for too long with a fixed display; replacement requires a donor CRT.
* Focus drift — adjust the focus pot on the flyback if accessible; if the CRT cannot focus, the cathode is end-of-life.