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Troubleshooting & Repair Model GFC7001E Carbon Dioxide Analyzer
Teledyne Analytical Instruments 286
At room temperature it should have approximately 30K Ohms resistance; near the 48
o
C set point it should
have ~12K ohms.
13.4.1.3. GFC Wheel Temperature
Like the bench heater above there are three possible causes for the GFC Wheel temperature to have failed.
1. The wheel heater has failed.
Check the resistance between pins 1 and 4 on the white five-pin connector just below the sample
temperature sensor on the bench (pin 1 is the pointed end).
It should be approximately 275 ohms.
2. Assuming that the I
2
C bus is working and that there is no other failure with the relay board; the solid-
state relay (K1) on the relay board may have failed.
Using the WHEEL_HEATER parameter under the signal I/O function, as described above, turn on
and off K1 (D2 on the relay board should illuminate as the heater is turned on).
Check the AC voltage present between pin 1 and 4.
CAUTION
ELECTRICAL SHOCK HAZARD
Hazardous Voltages are present during this test
3. If the relay has failed there should be no change in the voltage across pins 1 and 4.
K1 is socketed for easy replacement.
4. If K1 checks out OK, the thermistor temperature sensor located at the front of the filter wheel assembly
may have failed.
5. Unplug the connector labeled “Wheel”, and measure the resistance of the thermistor. The resistance
near the 68°C set point is ~5.7k ohms.
13.4.1.4. IR Photo-Detector TEC Temperature
If the PHT DRIVE test parameter described in Table 12-3 is out of range there are four possible causes of failure.
1. The screws retaining the IR photo detector to the absorption bench have become loose.
Carefully tighten the screws, hand-tight and note whether, after the analyzer has come up to
operating temperature, whether the PHT DRIVE voltage has returned to an acceptable level.
2. The two large transistor-type devices mounted to the side of the Absorption Bench have come loose
from the bench.
Tighten the retaining screws and note whether there is an improvement in the PHT DRIVE voltage.
3. The photo-detector has failed. Contact the factory for instructions.
4. The sync demodulator circuit board has failed. Contact the factor for instructions.