FANUC SP9018 Alarm 18: Program ROM Checksum Error and Troubleshooting

FANUC SP9018 indicates that the spindle amplifier detected an abnormal program ROM sum check. The spindle amplifier displays alarm 18. Depending on the CNC series and software, the CNC may show SP9018, another mapped spindle alarm number, or a general serial spindle alarm.

FANUC Maintenance Manual B-65285EN/04 describes alarm code 18 as “A sum check is abnormal.” The specified action is to replace the spindle amplifier or its control printed-circuit board. This is an internal amplifier hardware or program-ROM integrity fault; FANUC does not list a spindle parameter, motor, feedback cable, mechanical load, or PMC sequence as the normal cause.

For the surrounding spindle alarm numbers, see the FANUC Serial Spindle Alarm Codes SP9001–SP9033.

What Does FANUC SP9018 Mean?

The spindle amplifier control system uses program ROM to store the software instructions required for amplifier operation. A sum check is an internal integrity check applied to that stored program data. Alarm 18 is generated when the result is abnormal and the amplifier can no longer verify the program ROM data correctly.

The common service terms program sum check error, program ROM checksum error, and ROM sum check alarm refer to this same diagnostic direction. The wording program sum check error follows FANUC's αi Series alarm table, while ROM checksum error is a widely used search term.

The statement that alarm 18 is always caused by a communication failure between the CPU and ROM is too specific. FANUC's alarm 18 procedure confirms an abnormal sum check but does not define CPU-to-ROM communication as the universal cause. The fault may be located in the program ROM or related control-board circuitry, so diagnosis should remain at the control-board or spindle-amplifier level unless the manual for the exact unit provides a more detailed test.

Important: Confirm the Amplifier Display

FANUC alarm-number mapping varies among CNC generations. In B-65285EN/04, the same amplifier alarm 18 may be reported through different CNC alarm formats, including mapped alarms such as 750 or SP12xx on certain controls. Other alarm lists use SP9018.

For this reason, confirm all available displays instead of relying only on the article title:

• The spindle amplifier status display shows 18.

• The CNC shows SP9018, a mapped spindle alarm, or a serial spindle alarm corresponding to that amplifier.

• The alarm is coming from the spindle amplifier rather than the CNC's own ROM, FROM, SRAM, or part-program memory.

Record the alarm screen before switching off the machine. Also record the complete CNC model, spindle amplifier model and suffix, control-board number, spindle software series, and any maintenance performed immediately before the alarm appeared.

1. Do Not Confuse Program ROM With CNC Programs

The word program in “program ROM” refers to internal spindle-amplifier control software. It does not mean that a machining program, macro, ladder program, or customer part program contains an error.

Therefore, the following actions are not the official remedy for amplifier alarm 18:

• Editing or deleting an NC program

• Reloading machining programs

• Restoring CNC parameters without evidence of a separate data-loss alarm

• Changing spindle parameters

• Modifying the PMC ladder

• Replacing the spindle motor or feedback cable

These actions can introduce additional faults while leaving the ROM sum-check failure unchanged. Diagnose the actual amplifier display rather than another FANUC checksum or memory alarm that happens to use similar wording.

2. Determine Whether the Control Board Is Separately Serviceable

FANUC B-65285EN/04 permits replacement of either the complete spindle amplifier or the spindle amplifier control printed-circuit board for alarm 18. The correct repair level depends on the exact amplifier series, board construction, available service documentation, and replacement-part compatibility.

Before selecting a replacement, verify:

• The full spindle amplifier part number, including every suffix

• The control printed-circuit board number and revision, when separately identifiable

• The amplifier hardware series and rated specification

• Compatibility with the CNC and spindle software series or edition

• Connector layout and machine-specific installation requirements

Do not assume that a visually identical control board is interchangeable. A board or amplifier with incompatible identification or software support may produce another alarm, including FANUC SP9014 Alarm 14.

The official alarm 18 procedure does not prescribe repeated removal and reinsertion of the control board as the repair. If a board is replaced, however, it must be installed completely and all internal connectors must be seated according to the exact FANUC replacement procedure.

3. Replace the Control Board or Spindle Amplifier

If amplifier alarm 18 is confirmed, follow the applicable FANUC and machine-builder service instructions to replace the abnormal hardware.

Use control-board replacement only when:

• The installed amplifier series permits separate control-board service

• The exact compatible board and revision have been confirmed

• A qualified technician can perform the replacement and required verification

• The applicable documentation provides the correct procedure

Replace the complete spindle amplifier when separate board service is not supported, the correct board cannot be verified, or professional testing identifies a broader amplifier fault.

Before touching the amplifier, isolate machine power, follow lockout procedures, and wait for the DC link to discharge for the time specified in the applicable maintenance manual. Confirm the required safe electrical condition before opening or removing the unit. Spindle amplifiers contain hazardous voltages and should be serviced only by qualified personnel.

If replacement hardware is required, browse FANUC servo, spindle, and power drives or send REACO CNC the complete amplifier and control-board numbers for a compatibility check.

4. Retest After Replacement

After the correct replacement has been installed, restore all connections and covers and power up the machine according to the applicable procedure.

Confirm that:

• The spindle amplifier no longer displays 18

• The related CNC spindle alarm has cleared

• No new ROM, ID, software compatibility, or communication alarm appears

• The spindle amplifier completes startup normally

• The spindle operates correctly under the machine builder's controlled test procedure

If alarm 18 remains after control-board replacement, verify the replacement board number, revision, installation, and compatibility before replacing additional parts. If a different alarm appears, diagnose the new number separately.

Difference Between SP9016 and SP9018

Both alarms are internal memory-related faults, but they concern different memory types and tests:

RAM is working memory used while the control circuitry operates; program ROM stores internal control software. Do not treat alarm 18 as a RAM failure. For alarm 16, see the FANUC SP9016 Dual Check Safety RAM Error guide.

Difference Between Alarm 18 and Alarm 75

Alarm 18 and alarm 75 both involve software-integrity checks, but FANUC lists them as separate alarms:

Alarm 75 is specifically associated with Dual Check Safety in B-65285EN/04. Alarm 18 is not described there as a DCS-only alarm. Always follow the procedure for the number actually shown on the amplifier.

FANUC SP9018 Diagnostic Table

Recommended Troubleshooting Order

1. Confirm alarm 18 on the spindle amplifier and record the corresponding CNC alarm.

2. Record the complete CNC, spindle amplifier, control-board, and spindle-software identification.

3. Confirm that the fault concerns spindle-amplifier program ROM rather than CNC programs or another memory device.

4. Do not change parameters, ladder logic, motor wiring, or feedback components without evidence from another alarm.

5. Check the applicable FANUC manual to determine whether the control printed-circuit board is separately serviceable.

6. Verify the exact replacement board or amplifier, including every suffix and revision.

7. Isolate power and replace the control board or complete spindle amplifier using the specified procedure.

8. Retest startup and spindle operation; diagnose any new alarm separately.

Technical References

• FANUC AC Servo Motor αis/αi Series, AC Spindle Motor αi Series, Servo Amplifier αi Series Maintenance Manual, B-65285EN/04, Alarm Code 18

• FANUC AC Servo Motor αis/αi Series, AC Spindle Motor αi Series, Servo Amplifier αi Series Maintenance Manual, B-65285EN/03, Program Sum Check Error

• FANUC AC Servo Motor βi-B/βi Series, AC Spindle Motor βi Series, Servo Amplifier βi-B Series Maintenance Manual, B-65425EN/02, Spindle Alarm 18

Always use the manual edition that applies to the exact CNC, spindle amplifier, control printed-circuit board, spindle software, and machine configuration.

Need Help With FANUC SP9018 Alarm?

REACO CNC provides independent FANUC spindle amplifier testing, control-board repair, compatibility checking, and replacement support. Send us the CNC alarm screen, spindle amplifier display, complete CNC model, exact amplifier model and suffix, control-board number, and details of any recent replacement or repair.

Visit the FANUC Technical Support Center for more FANUC alarm guides, or contact REACO CNC for assistance.

Reference Source: Beijing FANUC. This article is based on FANUC technical documentation. Alarm-number mapping and the correct replacement level depend on the exact CNC, spindle amplifier, control board, software, and machine.