LI-COR LI-7500, Instruction Manual

Page: 97 / 155

Section 5
5-4 Maintenance
To check the fuse, power the unit off, disconnect the power to the unit, and open the case of
the LI-7500 control unit. The fuse is located on the main circuit board, in the lower lefthand
corner, as shown in Figure 5-2. Replacement fuses (part #439-04214, in the spares kit) plug
into the fuse holder; no soldering is required. Replace the fuse and close the LI-7500 case.
Replacing the Internal Chemicals
There are two small plastic bottles, each containing Ascarite II and magnesium perchlorate,
inserted into the analyzer housing that keep the detectors free of CO
2
and water vapor. These
bottles should be recharged with fresh chemicals on an annual basis. Replacement "charged"
bottles are available from LI-COR in sets of two under part number 7500-950. If you want to
recharge the bottles yourself, see Appendix C, Suppliers, for a list of suppliers of Ascarite II
and magnesium perchlorate.
NOTE: Calibration shifts will occur if CO
2
or H
2
O are not kept out of the analyzer
housing.
■
To change the sensor head soda lime/desiccant bottles:
1.
The plastic bottles are located in the analyzer housing in the sensor head. They are
accessed by removing the mounting bracket from the analyzer housing (Figure 5-3).
Remove the two screws on the bottom of the mount; be careful not to lose the spacers and
washers.