What are the common SLC loop trouble codes on the 6820, and how do I diagnose each one?

Common SLC loop troubles on the 6820 include DBL ADDR, Missing, GROUND FAULT, and SLC Loop Shorted. To diagnose these conditions, follow the specific procedures for each message:**

• DBL ADDR (Double Address): This occurs when an address is assigned to more than one detector. Correct the address following the SK and SD device procedures in the SLC Wiring Manual (Page 149) [1].

• Missing: This indicates devices are not being recognized. Verify hardware connections, wiring polarity, and ensure devices are connected to the SLC OUT terminals (not SLC IN) on expander modules (Page 149) [1].

• GROUND FAULT: This occurs when the panel senses current flowing to earth ground. Isolate the fault by removing wiring connections one at a time, pausing at least five seconds between each, until the fault clears. Note that a computer connected via USB or serial cable will also trigger this message (Page 149) [1].

• SLC Loop Shorted: This indicates a short circuit on the loop (Page 148) [1].

SLC Impedance Troubleshooting If devices are missing, use this procedure to verify loop integrity:

1. Disconnect both SLC wires from the panel terminal block.
2. Measure impedance from positive to negative and negative to positive; both must be greater than 500 k ohms.
3. Temporarily short the positive and negative wires at the point farthest from the panel.
4. Measure impedance at the panel wires; both measurements must be less than 50 ohms (Page 149) [1].