FANUC display ghosting: a repair record

This case records display ghosting on a FANUC 16 system on March 27, 2019. The original author judged the CRT monitor itself to be sound and continued checking the mainboard side; the display returned to normal after repair. The complete system suffix and board specifications were not recorded, so the tracing results below describe only the board examined at that time.

First locate the faulty side of the display chain

The recorded mainboard assembly comprised a MAIN board and an IO board, with the CRT connector on the IO board. Exchanging the IO board narrowed the author’s investigation to that board. This comparison is more targeted than replacing a monitor solely from the appearance of ghosting, but it does not establish that every FANUC 16 ghosting fault comes from the IO board.

Preserve this board’s signal-tracing record

The original notes trace signals from B34/B36 to the CRT connector, listing pin pairs 1/2, 3/4, 5/6, 12/16 and 18/14. Pins 1, 3 and 5 were identified as display-content signals, and 12 and 18 as vertical/horizontal signals. The inspection considered 12 and 18 normal and directed attention to 1, 3 and 5.

Tracing continued from 1, 3 and 5 through B34/B36 and resistors to 74F08. The record mentions O0, O1, O3 and A0B0, A1B1, A3B3, then follows A0, A1 and B3 to the CPU. These labels preserve the original inspection sequence, but no oscilloscope traces or complete schematic accompanied them. They cannot serve as pin definitions for other boards.

FANUC display ghosting repair record

FANUC display ghosting repair record

Result after finding an open connection

The author initially suspected a poor CPU-pin solder joint or trace corrosion. After removing the CPU, an open connection at one pin was found. Reconnecting the trace and resoldering the CPU restored a normal display in the test. The record confirms the open connection and the post-repair display result, not that corrosion necessarily caused the break.

How to use this historical case

The transferable approach is to distinguish the monitor from the controller side first, then narrow the fault along the signal path. The hardware-structure section of GFZ-62445E/03 shows connections between the control unit and CRT/MDI, but applies to 16/160/18/180-MODEL B. This case lacks the full model identification, so the manual cannot supply a missing board number or validate the listed pins for every Series 16 system.

For a similar problem, first save the nameplate, full board number, connection locations and fault-screen photos. Board-level desoldering, soldering and measurements require personnel with the relevant repair competence. For record organization, see the spare-part and equipment specification mapping; other cases are in the FANUC section.

References and applicability

• GE Fanuc Series 16/160/18/180-MODEL B Maintenance Manual GFZ-62445E/03 (body marked B-62445E/03; public mirror of the manufacturer’s manual): §2.1, Structure, printed page 90.