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Model 360E Instruction Manual TROUBLESHOOTING & REPAIR PROCEDURES
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.
11.4.1.3. 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 buss 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.
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.
11.4.1.4. 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.
05232 Rev B3 207