What is a servo press?

A servo press uses servo motors for precise force and position control during forming operations.

How do I calculate servo press tonnage?

Use our free tonnage calculator at servopress.club/tonnage-calculator.html

Fanuc Servo Alarm 445: FSSB Disconnection on Servo Press

admin

Fanuc alarm 445 (FSSB disconnection) is one of the more disruptive faults on servo press systems because it takes down all axes simultaneously.

## What FSSB Is

FSSB (Fanuc Serial Servo Bus) is the high-speed serial link between the CNC and servo amplifiers. On a servo press, this typically connects the CNC to 1-4 servo amplifiers depending on the press configuration (single-axis, dual-axis, or 4-point drive).

## Common Causes of Alarm 445

**Cable and connector issues (most common):**
- FSSB cable damaged or connector loose at CNC or amplifier end
- Cable routed near high-voltage conductors causing EMI
- Cable bend radius exceeded —FSSB cables have a minimum bend radius of 50mm

**Amplifier issues:**
- Amplifier power supply failure (check LED status on amplifier front panel)
- Amplifier overheating causing internal reset
- Multiple amplifiers on one FSSB chain —if one fails, all downstream lose communication

**CNC issues:**
- Axis card failure in CNC
- FSSB initialization parameter mismatch after parameter restore

## Diagnostic Steps

1. Check amplifier LED status —all amplifiers should show steady green on READY LED
2. Inspect FSSB cable connectors at both ends —reseat firmly
3. Check parameter 1023 (FSSB amplifier assignment) matches physical configuration
4. Swap FSSB cable with a known-good cable to isolate cable vs. amplifier fault
5. If alarm occurs intermittently, check for EMI sources near FSSB cable routing

## Parameter Check

On Fanuc 30i/31i/32i, verify:
- P1902: FSSB setting mode (0=automatic, 1=manual)
- P1910-1919: Amplifier assignment for each axis
- After any parameter restore, run FSSB auto-configuration (SYSTEM > FSSB > INIT)

## Typical Resolution

80% of cases: reseat FSSB connectors and reroute cable away from power cables. If alarm persists after cable check, replace FSSB cable (part number A66L-6001-0026 for standard 1m cable).

jim_applications

FSSB disconnection is one of the scariest Fanuc alarms because it kills all axes at once. The fiber optic cables that carry FSSB are fragile. I have seen them fail from being bent too tightly during installation, from vibration loosening the connectors, and from contamination on the fiber ends. Clean the fiber ends with isopropyl alcohol and lint-free wipes every 6 months. Keep spare cables on hand.

mike_chen_eng

On FSSB cable routing: we had a recurring 445 alarm that turned out to be the FSSB cable running parallel to the 400V motor power cable for about 600mm. Moving the FSSB cable to the opposite side of the cabinet and adding 100mm separation cleared the alarm permanently. EMI coupling on FSSB is easy to overlook because the cable looks fine physically.