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Maintenance
WARNING:
DO NOT TOUCH CAPACITOR C1 OR C2 OR THEIR
RELATED CIRCUIT FOILS. A SHOCK HAZARD MAY
EXIST.
Carefully remove the circuit board without touching any connections
which might lead to C1 or C2. After removal, discharge the two
capacitors by placing a jumper wire across each.
3. The anode voltage may also disappear or be greatly diminished
when condensation inside the sensor has occurred, shorting the
igniter to the sensor body across the wet insulator. This usually
occurs when the flame is turned on, if the sensor has not been
preheated for at least 1 hour.
5.1.3 Electronic Stability
If the checks outlined above indicate that conditions are normal,
allow the analyzer to run electronically with the collector cable
disconnected for several hours in the lowest range, and with the zero
offset value adjusted so that the recorder is reading midscale. If all is
normal electronically, a noise-free (pen width) recording, showing
absolutely no instability, should be obtained for as long as the analyzer
is allowed to run in this configuration. If the recording obtained is noisy
or erratic, replace the electrometer-amplifier PC board.
5.1.4 Printed Circuit Board Replacement
If performance is not adequate, then the analyzer must be
recalibrated as described in Section 4.6.14: Calibration before being
placed back in service.
Whenever the flame guard and anode power supply printed circuit
board have been replaced the analyzer must be recalibrated.
If the instrument performs as outlined in this section, the problem is
not related to the measuring circuit electronics.
5.1.5 Collector Cable
Before reconnecting the collector cable, check the continuity of the
center wire of the cable with an ohmmeter by measuring between the
center pins at each plug on the lowest resistance scale of the meter. Flex
the cable while making this measurement to be sure that there is not an
Teledyne Analytical Instruments
Model 4020
70
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