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7.1
Routine Maintenance
The only routine maintenance required is the periodic checking and replacement of the calibrating and
reference-gas cylinders. Note the supply pressure of flowing reference gas (if used), to avoid interruption
of continuous gas analysis if the supply becomes exhausted. Check the sampling system flow rate daily to
make certain that no blockage or buildup of particulates has occurred.
7.2
Parts Replacement
7.2.1 Sensing Unit
IMPROPER SENSING UNIT DISASSEMBLY
• Never open the 7866 Sensing Unit case until the line power has been disconnected at the 7866 Digital Controller.
• Always loosen the set screw provided on this model before turning the top threaded cover.
Failure to comply with these instructions could result in death or serious injury.
To remove the threaded cover, turn it counterclockwise and lift it off to expose all terminal board
connections.
To remove the sensor assembly from its housing, first remove all connections at the terminal board and
loosen the two screws (captive) in the cutouts at either side of the round circuit board. Carefully pull up on
the handle as shown in Figure 1-2 to withdraw the entire unit.
Circuit Card
Remove the sensor assembly as described above. Then loosen the two captive screws on the underside of
the plastic platform to free the entire circuit-card assembly. Carefully unsolder the 12 leads connecting the
circuit card and cell assembly. The solder posts to which each lead is connected is identified in Table 7-1
by the wire color code and the letters adjacent to each post. Note that two of the leads go to the jumper
posts (S&T) on the platform.*
*If the circuit card is replaced, note that the standard R18 for most standard ranges is 1.5 K ohms and the
new card may require the R18 resistor taken from the old card depending upon the range.
Cell-Block Assembly
Remove the circuit card as described above. It is necessary to unsolder the interconnecting wires. Remove
the two screws in the top platform and carefully separate the parts, sliding the platform along the wires.
Remove the two screws in the large plastic sleeve and carefully slide this along the wires.
This provides access to the top of the block, allowing removal of heaters and thermistors. Identify the leads
before unsoldering them from the bottom of the circuit card. See Table 7-1.
9/06
7866 Triple Range Digital H
7. Maintenance
and CO
Analyzer/Indicator - Operation and Maintenance
2
2
Maintenance
61
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Table of Contents
Troubleshooting
