Troubleshooting, continued
81
Problem Finding a fault by measuring line voltages in the field.
Solution When searching for a fault, you may need to measure the voltage on the two-wire
communications cable in the field. Set the voltmeter in the DC range and measure the voltage
at the L1 and L2 terminal strip. If the DC readings are erratic (changing every half second)
navigate the MDC Controller to the 50 Hz mode and switch the voltmeter to AC. Please see
Finding a short in the system on page 40. In he AC range, the voltmeter typically reads on the
high side, from 33 – 40 V. This is acceptable.
With the voltmeter set, go into the field and measure the two-wire communications cable (line)
at easy access points, either at a branch or inside a valve box where decoders connect. Remove
the DBY connectors and measure the cable.
If you need to measure in the middle of a cable, use a sharp knife to cut the insulation off the
cable and measure between the bare wires. Use DBY connectors to repair any cuts in the cable.
Problem The field decoders are not responding.
Solution If several field decoders are not responding, and they are located on the same branch,
the fault is probably with the cable. Please see the problem, Finding a break in the two-wire
communications cable on page 83.
If a single field decoder (or field decoders on separate branches) is not responding, you should
first test the field decoder to determine if the fault is in the decoder or the valve. Please see
Testing the operation of the decoders on page 37.
If the test results show the field decoder is not responding, (all three current readings are the
same, or very close), check the following reasons.
There is a fault in the cable leading to the unresponsive field decoder. Measure the voltage on
the decoder’s input wires. If the voltage is in the acceptable range (33 – 40 VAC), then check
the input connection to the decoder.
There is a fault in the field decoder. Check that the decoder address was entered correctly.
Please see Naming the Field Decoders on page 25.
There is a break in the solenoid. Measure the resistance in the solenoid. Standard Rain Bird
®
solenoids measure about 28 Ohms. If the resistance is low, replace the solenoid.
If the field decoder still does not respond, replace the field decoder.
To Next Page
Loading...
