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Troubleshooting and Service Teledyne API Model T360/T360M Operation Manual
246
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 factory for
instructions.
8.4.2. Excessive Noise
Noise is continuously monitored in the TEST functions as the STABIL reading
and only becomes meaningful after sampling a constant gas concentration for at
least 10 minutes. Compare the current STABIL reading with that recorded at the
time of manufacture (included in the T360 Final Test and Validation Data Sheet
shipped with the unit from Teledyne API).
1. The most common cause of excessive noise is leaks. Leak check and flow
check the instrument described in Section 6.3.
2. Dete
ctor failure – caused by failure of the hermetic seal or over-temperature
due to poor heat sinking of the detector ca To the optical bench. In addition
to increased noise due to poor signal-to-noise ratio, another indicator of
detector failure is a drop in the signal levels of the
CO
2
MEASURE signal
and
CO
2
REFERENCE signal.
3. Sync/Demod Board failure. There are many delicate, high impedance parts
on this board. Check the
CO2 MEAS and CO2 REF Test Functions via the
Front Panel Display.
4. The detector cooler control circuit can fail for reasons similar to the detector
itself failing. Symptoms would be a change in
MR RATIO Test Function
when zero air is being sampled.
Also check the SIGNAL I/O parameter
PHT DRIVE. After warm-up, and at
25
o
C ambient, if PHT DRIVE < 4800 mV, the cooler is working properly. If
PHT DRIVE is > 4800 mV there is a malfunction.
5. The +5 and 15 VDC voltages in the T360 are provided by switching power
supplies. Switch mode supplies create DC outputs by switching the input AC
waveform at high frequencies. As the components in the switcher age and
degrade, the main problem observed is increased noise on the DC outputs.
If a noisy switcher power supply is suspected, attach an oscilloscope to the
DC output test points located on the top right hand edge of the Relay board.
Look for short period spikes > 100 mV p-p on the DC output.
07272B DCN6552