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12
4.6
LOW-BATTERY DETECTOR
Low-battery detection is accomplished by comparing the
regulated voltage between V+ and common to the output of the
voltage divider (R107 and R110), which is connected across the
battery. When the battery voltage decreases, the output of the
voltage divider rises above analog common, causing
comparator U103A to change state. This action enables the LO
BAT annunciator on the display.
SECTION 5 SERVICE INFORMATION
5.1
DISASSEMBLY
The instrument must be opened to replace the battery, to select
three or four wire operation, or for calibration. Troubleshooting
or parts replacement may require more complete disassembly
(see Figure 5-1). The sequence below describes the basic
procedure for disassembling the instrument.
1. Remove the back cover.
2. At this point, you obtain access to replace the battery, select
three wire or four wire operation, or perform calibration.
Replace cover.
3. To remove the PC board, unscrew the standoff securing the
board to the front case. The board may now be pulled free,
although the wires to the probe jack will still be attached.
When the board becomes free of the case, the switch cover
will pull free as well. If necessary, the board can be pulled
completely free by detaching the wires at the board end. The
probe jack may then be removed, if necessary, by removing
the nut securing it to the case and pushing the jack free from
the inside.
CAUTION
Handle the PC board only at the edges, whenever
possible, to avoid possible contamination, which could
degrade instrument performance.
4. The LCD assembly may be removed from the PC board by
carefully spreading the clips that secure the display to the
board. Once the assembly is free of the board, the various
parts will be loose, so handle the LCD with care.
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