Tag: 935 SRAM ECC ERROR

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Fanuc Oi Mate TC Controller 935 SRAM ECC ERROR

This is one of the more common and serious errors in the Fanuc control system. Let’s analyze the causes and handling directions:

935 SRAM ECC ERROR

1. Alarm Meaning

SRAM ECC Error: The system has detected a checksum error in the SRAM memory.

ECC (Error Checking and Correction) is an error-detection mechanism. This alarm is triggered when data in the SRAM (battery-backed memory or system RAM) is corrupted.

The alarm code 935 generally indicates:

  • Corruption of SRAM data bits
  • Failure of the memory chip itself
  • Loss of data due to battery power failure or insufficient charge

2. Possible Causes

  • Damage to the SRAM chip on the motherboard (a common hardware aging issue)
  • Battery depletion or poor battery contact → Loss of SRAM data
  • Corruption of parameter files (caused by abnormal shutdowns or interference)
  • Failure of the control board itself (CNC Main Board)

3. Typical Symptoms

  • The system fails to start normally (as seen in your video, stuck at the alarm screen).
  • Repeated reboots may still result in the same alarm.
  • Occasionally, the system may boot, but all parameters are lost.

4. Solution Steps

A. Check the Battery

  • Open the control cabinet and locate the Fanuc SRAM backup battery (usually a lithium battery, 6V or 3V × 2 in series).
  • Measure the voltage. If it is < 5.6V (for a 6V battery) or < 2.9V (for a single 3V battery), it must be replaced.
  • When replacing, ensure the controller remains powered (to avoid data loss due to power failure).

B. Attempt to Clear SRAM and Reinitialize

  • Enter the system maintenance mode (BOOT/INITIALIZE).
  • Execute SRAM CLEAR (clear the memory).
  • Reload the PMC Ladder, system parameters, and machine parameters.
  • Requires backup parameters provided by the original machine tool manufacturer (important!)

C. If the Error Persists After Clearing

  • There is a high probability of a hardware failure in the motherboard’s SRAM.
  • The motherboard (CNC board/Memory Board) needs to be replaced.
  • Experienced maintenance engineers may attempt to replace the SRAM chip, but replacing the entire board is generally more reliable.

5. Recommended Immediate Actions for This Problem

  • First, check the battery voltage → If the battery voltage is low, replace the battery and attempt to power on again.
  • If the battery is normal → Enter maintenance mode, clear the SRAM, and reload the parameters.
  • If the error persists after clearing → It is likely a motherboard hardware failure, requiring repair or replacement.

⚠️ Note:

  • Clearing the SRAM will result in the loss of machine tool parameters. Always have a backup file (from a CF card, PC card, or obtained from the manufacturer).
  • Without parameter backups, even if the error is cleared, the machine tool cannot be restored to normal operation.