Teledyne GFC-7000T - Trace CO2 Analyzer - manual - Manual (Page 263)

Troubleshooting Model GFC7000TA Carbon Dioxide Analyzer
Teledyne Analytical Instruments 245
3. If the drive voltage is correct in step 2, then remove the source from the heat sink assembly (2
screws on top) and connect to its mating connector. Observe the light being emitted from the
source. It should be centered at the bottom of the U-shaped element. If there is either no
emission or a badly centered emission then the source is bad.
10.5.7.5. Pressure/Flow Sensor Assembly
The pressure/flow sensor PCA, located on the top of the absorption bench, can be checked with a
Voltmeter using the following procedure which, assumes that the wiring is intact, and that the
motherboard and the power supplies are operating properly:
1. For Pressure related problems:
 Measure the voltage across C1 it should be 5 ± 0.25 VDC. If not then the board is bad.
 Measure the voltage across TP4 and TP1. With the sample pump disabled it should be 4500
mV ±250 mV. With the pump energized it should be approximately 200 mV less. If not, then
S1, the pressure transducer is bad, the board is bad, or there is a pneumatic failure
preventing the pressure transducer from sensing the absorption cell pressure properly.
 For flow related problems:
 Measure the voltage across TP2 and TP1 it should be 10 ±0.25 VDC. If not then the board is
bad.
 Measure the voltage across TP3 and TP1. With proper flow (800 cc/min at the sample inlet)
this should be approximately 4.5V (this voltage will vary with altitude). With flow stopped
(sample inlet blocked) the voltage should be approximately 1V. If the voltage is incorrect, the
flow sensor is bad, the board is bad or there is a leak upstream of the sensor.
10.5.8. Motherboard
10.5.8.1. A/D Functions
The simplest method to check the operation of the A-to-D converter on the motherboard is to use the
Signal I/O function under the DIAG menu to check the two A/D reference voltages and input signals that
can be easily measured with a voltmeter.
1. Use the Signal I/O function (See Section 10.1.3 and Appendix A) to view the value of
REF_4096_MV and REF_GND. If both are within 3 mV of nominal (4096 and 0), and are stable,
±0.5 mV then the basic A/D is functioning properly. If not then the motherboard is bad.
2. Choose a parameter in the Signal I/O function such as SAMPLE_PRESSURE, SAMPLE_FLOW,
CO
2
_MEASURE or CO
2
_REFERENCE . Compare these voltages at their origin (see interconnect
drawing 04215 and interconnect list 04216) with the voltage displayed through the signal I/O
function. If the wiring is intact but there is a large difference between the measured and
displayed voltage (±10 mV) then the motherboard is bad.