Service and troubleshooting
8.40 EST3 Installation and Service Manual
Figure 8-9: Signature data circuit ground faults
To isolate the ground fault, open the suspect circuit (both
conductors) at a location that will disconnect approximately 50%
of the installed devices. Figure 8-10 illustrates the technique on a
data circuit. A similar technique is used on smoke power or
module input circuits to isolate ground faults.
Figure 8-10: Ground fault isolation
If the LCD Ground Fault LED goes out, the ground fault is
located on the portion of the circuit that has been disconnected.
If the LCD Ground Fault LED remains on and no devices
restore, the short has been isolated to the first 50% of the circuit.
Re-connect the previously isolated portion of the circuit, and
open the circuit at a new location. If during the first open circuit
test the Ground Fault LED went off, open the circuit at a location
“electrically farther” from the Signature controller module, and
repeat the test. If during the first open circuit test the Ground
Fault LED remained on, open the circuit at a location
“electrically closer” to the 3-SSDC(1), and repeat the test.
Continue to increase or decrease the number of devices on the
opened circuit leg and you will eventually isolate a single device
or wire segment that is causing the problem.
The ground fault detection circuitry requires approximately 30 to
40 seconds to respond when the fault is removed.
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