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FANUC Controller
System · Intermediate · 30-60 minutes
Fanuc Alarm 935 - SRAM ECC ERROR
Alarm 935 SRAM ECC ERROR indicates that the CNC detected an error correction code failure in the static RAM module, meaning the memory has corrupted data that cannot be automatically corrected. This is typically caused by a failing or depleted battery allowing SRAM data corruption, a defective SRAM module itself, or less commonly a failing CPU board with corrupted memory circuitry.
935
Fanuc Alarm 935 - SRAM ECC ERROR
PROGRAM ALARM 935
SRAM ECC (error correcting code) error detected. SRAM module is defective. Check battery and replace SRAM or CPU board as needed.
Root Cause Summary
Alarm 935 SRAM ECC ERROR indicates that the CNC detected an error correction code failure in the static RAM module, meaning the memory has corrupted data that cannot be automatically corrected. This is typically caused by a failing or depleted battery allowing SRAM data corruption, a defective SRAM module itself, or less commonly a failing CPU board with corrupted memory circuitry.
Causes and Fixes
- 1
Check battery voltage at the CPU board battery connector using a multimeter. For 0i/16i/18i series, verify voltage is above 3.0V DC (nominal 3.6V). For 30i/31i/32i series, check both main board battery and optional APC battery if equipped.
Do not disconnect battery while CNC is powered on, as this will cause immediate parameter and data loss.
- 2
Navigate to SYSTEM > BATTERY screen (or MDI > SYSTEM > BATTERY on newer controls) to check battery voltage display. Low battery voltage reading below 3.0V confirms battery depletion.
- 3
Replace battery with OEM Fanuc battery (A98L-0031-0025 or equivalent for your series). After replacement, clear alarm, power cycle the CNC completely, then restore parameters from verified backup and re-home all axes.
Parameters, offsets, and programs will be lost during battery replacement if CNC power is not maintained. Ensure complete backup exists before proceeding.
- 4
After restoration, monitor DIAGNOSIS screen #700-#703 (battery voltage diagnostics) over several days to confirm battery is maintaining proper voltage and alarm does not recur.
Call a technician if:
- ·CPU board replacement required
- ·Multiple simultaneous system alarms
- ·Repeated failures after component replacement
Prevention
- Replace backup battery every 2-3 years
- Maintain proper grounding and EMI shielding
- Keep control cabinet temperature below 40°C
- Perform regular memory diagnostics
Common Mistakes
- Replacing SRAM without checking battery first
- Not backing up parameters before memory replacement
- Ignoring EMI sources during troubleshooting
- Using incorrect SRAM module part numbers
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