Issue
Fault Finding on an IC-SNP / IC3-SNP and associated IAC controllers.
Product Line
Satchwell BAS & Sigma
Environment
- IC-SNP
- IC3-SNP
- IAC controllers
Cause
Communication faults on the SubLAN may be caused by:
| Cause | Description |
|---|---|
| Incorrect LAN Termination | Missing or improperly placed 120-ohm resistors can cause signal reflections and data corruption. |
| Biasing Misconfiguration | Bias jumper not set to “D” (Full Biasing) can result in unstable idle voltage levels. |
| Faulty Controller Driver | A single IAC controller with a failed RS-485 driver can hold the RX line low, blocking communication. |
Corrupted gateway.txt Entries |
Invalid or misconfigured entries can prevent the IC-SNP from initializing communication properly. |
| Physical Layer Issues | Damaged cables, poor connections, or incorrect wiring can interrupt signal transmission. |
| Power Supply Problems | Inadequate or unstable power to controllers can cause intermittent or complete communication loss. |
| IC-SNP Hardware Failure | Internal faults in the IC-SNP or IC3-SNP can prevent proper LAN operation. |
| Excessive LAN Length or Load | Too many devices or long cable runs without repeaters can degrade signal quality. |
| Environmental Interference | Electrical noise from nearby equipment can disrupt RS-485 signals. |
Resolution
1. Use of Alarm Manager
- Access via Sigma default/backup server.
- Review system messages (priorities 22–30) for controller-specific errors.
- Look for messages like “Unable to Communicate with Controller ???”.
2. Troubleshooting gateway.txt File
Symptoms:
- “Unable to open gateway.txt file” error.
Steps:
- Start with a minimal gateway.txt (1–2 entries).
- Use a known-good version from Exchange-On-Line.
- If errors persist:
- Remove all entries except one.
- Download and warm-start the controller.
- Gradually reintroduce entries to isolate the faulty line.
3. Controller Not Responding
Single Controller:
- Check local communication using Visisat and LIB-4-485.
- Verify LAN wiring and power supply.
Multiple Controllers:
- Indicates partial or full SubLAN failure.
- Begin investigation at the IC-SNP.
4. IC-SNP Hardware Checks
| Component | Expected Behavior |
|---|---|
| Bias Jumper | Set to D (Full Biasing) |
| Termination | 120-ohm resistors at both ends |
| Channel 2 TX LED | Flashes after warm-start (gateway.txt processing) |
| Channel 2 RX LED | Flashes if receiving replies |
RX LED Permanently On:
- Indicates a faulty IAC controller driver disrupting LAN comms.
5. IC-SNP Retry Mechanism
- Retries each controller 3 times before marking offline.
- Sends error to Alarm Manager.
- Retries offline controllers every 30 minutes (on the hour and half-hour).
6. Binary Chop Method for LAN Isolation
Purpose:
Efficiently isolate faulty segments or controllers.
Steps:
- Identify LAN midpoint.
- Disconnect twisted pair at nearest controller.
- Observe RX LED behavior:
- LED Off: Fault lies beyond midpoint.
- LED On: Fault lies before midpoint.
- Repeat by halving LAN again (25% or 75%) until fault is found.
7. Voltage Testing Guidelines
Use a DC voltmeter to measure:
| Measurement | Expected Voltage |
|---|---|
| +ve to 0V | ~2.5 V |
| –ve to 0V | ~0.15 V |
| +ve to –ve | ~2.31 V |
Note:
- Negative voltages suggest LAN faults.
- Compare readings across segments to identify anomalies.
8. RX LED Not Flashing at All
Possible Causes:
- Faulty IC-SNP
- Faulty SubLAN
- Faulty Controllers
Steps:
- Disconnect LAN after first controller.
- Warm-start IC-SNP.
- Observe RX LED:
- If flashing resumes, use binary chop to isolate fault.
- If not, test cable and controller individually.
9. Cable Testing Procedure
- Disconnect both ends and separate cores.
- Measure resistance:
- Between cores: ∞
- Each core to earth: ∞
- Short cores at one end.
- Measure resistance at other end:
- Between cores: ~0 Ω
- Each core to earth: ∞
10. Controller Testing
- Use LIB-4-485 and Visisat Engineering software.
- Confirm controller responds to direct communication.
Final Steps:
Once faults are resolved:
- Download full gateway.txt.
- Warm-start IC-SNP.
- Monitor Alarm Manager for new errors.
