c. Check the Battery Charger (NiCad). Refer to Appendix E, Monitor Board
Power Supply Schematic, section D-22.
(1) Disconnect the battery from the charging circuit and substitute a resistive
load of 75 ohms ( 5 percent). This load should have a power rating of approximately 5
Plug the unit into an outlet. The rest of the unit should remain turned off.
(3) Place an milliampere (ma) meter in series with the 75 ohm load. Adjust
RA2 until the meter reads 250ma. Short circuit the load for a few seconds at a time. The
current should not increase by more than 70ma, showing correct action of the current
(4) Turn on the unit. With nominal line voltage (120v or 230v RMS), the
charge current should not fall by more than 60ma. The voltage across the load resistor
should be at least 14vdc with the unit turned off. A discharged NiCad battery in good
condition should recover 100 percent of its charge in 14 hours at room temperature
(approximately 70 degrees Fahrenheit).
d. Check the Low Battery Shut-Off. Refer to Appendix E, Monitor Board Power
Supply Schematic, section E-24.
Unplug the unit from line.
(2) Remove the battery completely and connect, in its place, a variable dc
power supply from 9v to 14v and 2 amps current capability.
Set the supply voltage to 12.0v.
Turn on the unit.
(5) After the trace is stabilized, lower the voltage gradually until the unit shuts
off. This should occur at 9.5v. If this is not the case, adjust RA16 (four-turn control) and
repeat the procedure until the low voltage shut off is correct.
(6) Check the hysterisis control by increasing the power supply voltage to
11.0v. Leave the monitor on/off switch on and allow the low voltage shut off to turn the unit
off. The unit should not turn itself on below this voltage.
e. Check the Overall Battery Current.
(1) With the same set up as described under low battery shut off calibration,
connect a dc ammeter (0-2A) in series with the positive lead of the power supply.