Scale-Tronix 5002 - Page 25

Voltage step-down and isolation is provided by power
transformer Tt. A dual primary winding is provided
to allow operation at either 120 VAC or 240 VAC.
The power supply is protected against faults by a
fuse or fuses wired into the primary circuit, depending
on the scale's particular configuration.
Depending on the particular scale and configuration,
a special safety rated capacitor may be used to
remove noise from the AC line which might interfere
with the scale's operation. An additional capacitor,
and a fertite toroid, may be added fo the primary
wiring to form a complete line filter.
Full-wave rectification of the transformers secondary
voltage is provided by diodes CR-1 and CR-2.
Capacitor C-1 provides filtering. A power-on indicator
is provided by light-emitting diode LED-1 and resistor
R-1. Diode CR-3 prevents the battery from
discharging into the power-on indicator and connects
the rectified, filtered DC voltage to output connector
4-1 for use by the scale's instrument board.
The 6.0 voit nickel-cadmium battery, composed of
five (5) size “AA” cells, is charged by the current
through resistor R-2. Schottky diode CR-4 is used as
a “switch” to couple the battery voltage to output
connector J-1 when AC power is removed and the
battery is need to operate the scale.
A charge indicator circuit is provided by transistor Q-1
and light emitting diode LED-2. The voltage across
charging resistor R-2 is monitored by Q-1, a pnp
darlington transistor. Resistor R-3 provides current -
limiting for Q-1's base. When the battery is properly
connected and charging, Q-1 will be switched "on"
and provide a current path through limiting resistor R-
4 and the "CHARGE" indicator located on the front
panel of the readout. Note that if the battery is
disconnected from the power supply board; or the
power cable, instrument board, display cable, or
display board are disconnected, the LED-2 charge
indicator will not light.
4.40.2 MODEL 23PWR-7 POWER SUPPLY
This is a larger power supply that is used in
conjunction with a 7.2 volt, 1500 Milli-amp hour
nickel-cadmium battery pack. The larger battery pack
is needed to operate the internal printer option on the
mode! 6102 and other scales,
Voltage step-down and isolation is provided by power
transformer T301. A dual primary winding is provided
to allow operation at either 120 VAC or 240 VAC. The
power supply is protected against faults by two fuses
wired into the primary circuit, which are mounted in
holders on the pawer supply board.
Capacitor "CF", a special safety rated capacitor, is
used to remove noise from the AC line which might
interfere with the scale's operation. An additional
capacitor, and a ferrite toroid, may be added to the
primary wiring to form a line filter.
Diode rectifiers D301, D302, D303, and D304 are
connected on T301's secondary to form a ful-wave
rectifier network with center-tap. Use of the center-
tapped configuration provides two output voltage
levels: А lower level for operating the scale's
electronics, and a higher voltage to charge the battery
pack.
Diode D305 connects the lower rectified voltage to
capacitor C301 for filtering. This prevents the filtered
DC voltage from appearing in the battery charging
circuit. A power indicator is formed from the network
of LED301 and current limiting resistor R301. Diode
D306 connects the rectified, filtered DC voltage to
connector J301 for use by the scale's instrument
board.
The 7.2V battery pack consists of six (6) size "C*
cells. Charging current for the battery pack is supplied
through R303. No provision is made to fitter this
charging voltage.
Since the battery charging voltage is doubied in
respect to the scale's operating voltage, operating the
scale without the battery could apply potentially large
voltages to the readout's instrument board. Zener
diodes D309 and D310 clamp this voltage to a safe
level if the battery is removed. Diode D308 is
provided to prevent damage to D309 and D310 if the
battery is somehow incorrectly connected.
The battery pack is directly connected to connector
J302 to provide voltage to operate the internal printer.
Diode D307, a schottky rectifier, is used to couple the
battery voltage to the instrument board when AC
power is not present.
Palymer fuse F303 is used to protect the battery pack
from damage should a short occur in the scale's
$002, 5102, 5602, 6002, 6102, 6202, 6502, 6702 23