Power Supply; Troubleshooting Procedures; Display Does Not Illuminate; Weight Reading Not Accurate - Grainger 4802 Operating And Service Manual

Diodes D1 and D3 are used to turn the scale "on"
when either the front panel "ON / (OFF) / ZERO" or
the "RECALL PRIOR WEIGHT" pushbuttons are
pressed. They connect the "ON" line present on the
expansion bus connector J1 to ground momentarily to
cause the power to the instrument board to become
active. Diodes D2 and D4 are included to couple the
pushbutton closures to I/O expander U4 so that the
microcomputer U10 can determine which pushbutton
has been activated and take the appropriate action.
4.29

POWER SUPPLY

The power supply is mounted external to the scale
cabinet on the rear panel. It is connected to the scale
via a removable power input connector. A hospital
grade line cord and plug is provided. The power
supply is a separate sealed medical power supply
with UL and other certifications.
power supply capable of operating from 100 to 240
volts with no switching or change in connections
required. For 240-volt operation, the line cord and
plug must be replaced with the appropriate cord for
the country of use. The output voltage is 12 volts DC.
4.30

TROUBLESHOOTING PROCEDURES

The following simplified troubleshooting procedures
are recommended for identifying defective system
components. Certain corrective measures are
provided. More complicated servicing should only be
performed by the factory or authorized service
facilities. Most problems can be solved over the
telephone. Problems requiring factory service are
usually handled quickly and the scale is on its way
back within 48 hours.
problem.
4.31

DISPLAY DOES NOT ILLUMINATE

Check that the scale is plugged in. Check that the
batteries are properly installed and in good condition.
Check that the cable between the display board and
instrument board is connected.
membrane keyboard is connected to the display
board. Measurements of the D.C. supply voltages
can be made with a DVM.
4.32

WEIGHT READING NOT ACCURATE

This is commonly caused
obstruction of the weighing cradle. Check that the
cradle is not touching some foreign object so that it is
restricted in its downward movement. Also check that
the connecting cable is firmly plugged into the
instrument circuit board (marked "J4 LOAD CELL").
It is a universal
Call first to discuss the
Check that the
by a mechanical
4.33 WEIGHT READING TAKES EXCESSIVE
TIME TO DISPLAY
If the cradle is in motion, the scale will wait for it to
settle before displaying the weight.
caused by excessive patient motion.
Also check that the transducer cable is firmly plugged
into the instrument board. Examine that the cradle is
not rubbing against a foreign object. Check that the
scale is not subject to excessive vibration or breezes
from overhead fans or ventilation outlets.
SCALE
4.34
"O-LOAd"
The message "O-LOAd" indicates the weight signal
is larger than the maximum value allowed (see
specifications on inside front cover). If the weight
value is within the specified range this could indicate
a damaged transducer or defective instrument board.
The "CAbLE" display indicates a signal outside the
range of the internal a-d converter has been applied.
This can be caused by a weight that is well in excess
of the scale's capacity or a damaged or disconnected
transducer cable. Check the internal connection of
the four wire cable to the "J1 LOAD CELL" connector.
4.35 READING DOES NOT CHANGE WHEN
WEIGHT APPLIED
The load cell transducer, connector or cable may be
defective. The load cell transducer's continuity and
resistance can be checked with an ohmmeter after
unplugging from the readout. The proper resistance
values are listed below:
WIRE COLORS (PIN NO.)
GRN(1)/BLK(2)/WHT(3)/RED(4) >10MΩ
to scale frame
GRN(1) to BLK(2)
WHT(3) to RED(4)
Consult factory if readings differ from those shown.
NOTE: Ohmmeters will not indicate a change in
resistance of the load cell transducer when weights
are applied to scale. This is due to the extremely
small change in resistance of the strain gauges
employed (<1 ohm) and the fact that the bridge
configuration presents a constant value of resistance
17
This can be
DISPLAYS "CAbLE"
RESISTANCE
350-450Ω
325-375Ω
OR