FANUC Alarm History and Operation History: Using 3106#4 OPH to Trace Intermittent Faults

Bit definitions, screen paths and recorded data here come from the OPERATION HISTORY / external operator message record chapter of the official FANUC (GE Fanuc) maintenance manual for Series 16/160/18/180-Model B (document A16B-1211-0090), cross-checked against Chinese field notes on 3106#4. Bit numbers and softkey names vary by series and software version – always confirm against the machine’s own parameter manual and record original values before changing anything.

30-second check

1. Why intermittent faults require history

The hardest fault is the one that is healthy whenever you look at it. The value of alarm and operation history is not the alarm number (you can see that live) but what happened in the seconds around it:

• Did someone switch to MDI, change an offset, or jog an axis just before the alarm;
• Did an input signal (door, clamp, pressure, tool position) toggle at that instant;
• Which program block and which M-code were executing;
• Did a second alarm follow immediately (do not reverse cause and effect).

This site’s guide to the four FANUC diagnostic screens covers current state; this article covers recorded history. They complement rather than replace each other: confirm the symptom with live diagnostics, then reconstruct the timeline from the history.

2. Opening the two history screens

Table 1 Bits and parameters stated in the official maintenance manual

The manual’s display path: press SYSTEM, then the continue softkey [>], then [OPEHIS] / [OPRT] appear; press [OPEHIS] twice to open the operation history screen, and use the bottom menu for the most recent entries. An external operator message may be up to 255 characters; the record count and characters per record are selected by the MS1/MS0 combination.

Alarm history and operation history are different screens: the former mainly stores alarm numbers and occurrence times, while the latter combines key operations, signal changes, alarm details and timestamps – much better for a timeline. Softkey names and menu positions vary by series, software version and builder customisation.

3. Correction: do not swap 3106#4 and #7

Table 2 Circulating bit definitions versus the official manual

This trap is subtle: setting #7 to 1 because you think it enables the display leaves the screen visible but sampling switched off, so every subsequent intermittent fault goes unrecorded – worse than never enabling it. After any change, trigger a reproducible minor alarm and confirm that a new entry appears.

4. Alarm history vs operation history vs diagnostics

Table 3 What each data source records

Recommended order: alarm history to fix the time -> operation history for the surrounding actions -> live diagnostics for the present state -> ladder monitor or Servo Guide waveform if needed. Staring at live diagnostics first usually ends with “everything is fine now”.

5. Building a four-column timeline

One row with four columns is worth more than ten random screenshots:

1. Alarm time: read the timestamp from alarm history; if 3122 is set too coarse, operation-history time points are approximate – check first;
2. Operator actions: which MDI key operations and which signal ON/OFF changes sit immediately before and after that instant;
3. Program block: map it to the part program – which block, which M/S/T code;
4. External conditions: shift, tool number, workpiece, temperature/air pressure, whether a door was opened or material changed.

If the CNC clock is wrong, the whole timeline is wrong. Verify the control date/time first before aligning it with camera footage or shift logs.

6. Three typical reconstructions

None of these are “change one parameter” problems. The timeline narrows suspicion from the whole machine to one signal or one program block, so you can monitor that point deliberately.

7. Capturing evidence and handover

• History is not an archive: changing MS1/MS0 clears records, some parameter changes require a power cycle, and capacity depends on the model -> screenshot key evidence immediately;
• Screenshots should include the screen title, system time and full alarm text, ideally with the program block number;
• A handover pack should contain: alarm history screenshot, operation history screenshot, parameter and ladder exports, program version, and who changed what;
• For long-term retention, export on a schedule per company/builder practice – do not expect the CNC to keep months of history;
• Before changing 3106#4/#7, 3112 or 3113, record the original values, and restore or document the change after diagnosis.

Frequently Asked Questions

Where is the FANUC alarm history screen, and why is it missing on my machine?

Look under SYSTEM and the continue menu for [OPEHIS] or a history softkey – names vary by series and software version. If there is no entry at all, the display switch is usually off: in the official manual 3106#4 (OPH) controls display of the operation history screen (0 not displayed / 1 displayed), while 3106#7 (OHS) controls sampling (0 sampled / 1 not sampled). The function may also be unavailable or the menu customised by the builder. Record original values, then trigger a reproducible minor alarm to confirm a new entry appears; confirm bit numbers in the machine’s own parameter manual.

Is alarm history cleared when power is turned off?

There is no uniform guarantee. What the official manual does confirm: external operator message history is cleared when the MS1/MS0 bits of 3113 are changed, and changing 3112#2 OMH requires a power cycle; the number of records and characters per record are parameter-dependent. Whether records survive power-off and how many are kept varies by model, firmware and parameters – check the shipped manual. Treat history as temporary evidence, not an archive: capture screenshots or exports as soon as a critical fault occurs.

What does each history record, and which should I check first for an intermittent fault?

Alarm history mainly holds alarm numbers and occurrence times. Operation history, per the official manual, records MDI key operations, ON/OFF changes of selected I/O signals, NC alarm details and date/time stamps – a timeline with context. Start with alarm history to fix the time, use operation history for the surrounding key and signal activity, return to live diagnostics for the present state, and add ladder monitoring if needed. Looking only at live diagnostics usually ends with “everything is normal now”.

Last updated: 2026-11-08

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