Teledyne GFC-7000T - Trace CO2 Analyzer - manual - Manual (Page 257)

Troubleshooting Model GFC7000TA Carbon Dioxide Analyzer
Teledyne Analytical Instruments 239
3. If the relay has failed there should be no change in the voltage across pins 2 and 4 or 3 and 4.
NOTE: K2 is in a socket for easy replacement.
4. If K2 checks out OK, the thermistor temperature sensor located on the optical bench near the
front of the instrument could be at fault. Unplug the connector labeled “Bench”, and measure the
resistance of the thermistor. At room temperature it should have approximately 30K Ohms
resistance near the 48
o C set point it should have ~12K ohms.
10.4.1.3. 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 Pin 4.
WARNING:
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. NOTE: 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. Unplug the connector labeled “Wheel”, and measure the resistance of
the thermistor. The resistance near the 68
o C set point is ~5.7k ohms.
10.4.1.4. IR Photo-Detector TEC Temperature
If the PHT DRIVE test parameter described above in Table 11-2 is out of range there are two 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.