7. Error Messages and Diagnosis
This procedure requires access to the circuitry of a unit connected to live power. Dangerous accidental contact
with line voltage is possible. Only qualified personnel are to perform these procedures. Potentially lethal voltages are
present.
Experience has proven that many control problems are not caused by a defective instrument. See the chart below and
table 7.1 for some of the other common causes of failures.
• Line wires are improperly connected
• No voltage between line terminals
• Incorrect voltage between line terminals
• Connections to terminals are open, loose, or missing
• Thermocouple is open at tip
• Thermocouple lead is broken
• Shorted thermocouple leads
• Short across terminals
• Open or shorted heater circuit
• Open coil in external contactor
• Burned out line fuses
• Burned out relay inside control
• Defective solid-state relays
• Defective line switches
• Burned out contactor
• Defective circuit breakers
If the points listed on the chart have been checked and the controller still does not function, it is suggested that the
instrument be returned for inspection. Do not attempt to make repairs. Be sure to use adequate packing materials to
prevent damage during shipment.
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