5.23
5.2.2.3 Heater Control Circuit Tests
1. Remove the power supply unit from the analyser (See 2.6.1 Paragraphs 1 to 3).
2. Remove connector from TB-B.
3. Connect a load to simulate the heater resistance (see Table 5.2) or reconnect the heaters.
4. Connect an ammeter in series with the heaters and measure the current flowing. The
current should be less than 5mA.
5. Connect a 150ohm, 2%, 0.5W resistor temporarily between TB-B-1 and TB-B-6.
6. Measure the heater current. This should agree with the value in table 5.2.
7. If test 6 fails, replace the PCB 01100919. If test 6 is satisfactory the fault probably lies
with the microprocessor board 01100918C or 01100918D. Check by substitution.
8. Replace the connector on TB-B.
9. Replace the power supply unit into the analyser. See Section 2.6.1 Paragraphs 5 - 7.
5.2.3 Heater Resistance
Measuring the resistance of the heater in the Transducer unit gives an indication of failed heater
elements.
Measure heater resistance by removing the heater wires from the power supply connector TB-A.
Compare the resistance with the values shown in Table 5.2.
If the meter indicates open circuit check the continuity of any connecting cables.
The resistance of the heaters depends upon type of Transducer used.
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