Fanuc alarm 404: ECC UNCORRECTABLE ERROR

What it means

An ECC-protected memory area suffered a multi-bit error that hardware correction could not fix, so the CNC halted. Single-bit errors are corrected silently; an uncorrectable error means real data corruption in main memory. As with other bus/memory alarms, the PCB identified on the third line of the screen should be replaced first, and external noise ruled out.

Likely causes

• Defective DRAM on the main board or slave PCB
• Grounding/noise problems in the cabinet

Replacement parts

We supply the following units for this alarm — tested, warranty-backed:

• Main board (or PCB named on third line)

  board · Common cause

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