CHAPTER 3 MAINTENANCE PROCEDURES
Ohaus Corporation www.ohaus.com
14
Navigator Series Service Manual
3.3 REPLACING THE LOAD CELL
The Load Cell may need to be replaced because of scale instability, or because the scale does not
calibrate or repeat, or because it is physically broken or displays an error code.
Disassembly:
1. Open the scale
– see Section 3.2. Verify that there is no mechanical interference, pinched wire
or bad solder connection that may be causing the load cell to appear defective.
2. Remove the Load Cell
– turn the scale over, holding the Load Cell by hand, and remove the 2
load cell screws from the bottom housing. The NV model uses cross-recess screw heads (Phillips
type) while the NVT use hex socket head screws.
3. Turn the scale back on its feet and gently lift off the Load Cell, the attached PCB and the AC
Adapter cable. Place the Load cell and the PCB on a static protected work area.
4. The load cell connection is a five-wire cable that is soldered directly to the PCB. Before
disconnecting the cable record the wire colors and their location on the PCB. (Hint: A digital picture
is an easy and reliable record.) Disconnect the cable connecting the PCB to the Load Cell by un-
soldering the 5 wires from the PCB. Take care not to over heat the PCB which will damage the thin
PCB conductors.
Re-Assembly:
1. Re-solder the new load cell to the PCB, connection J3.
NOTE:
The spare part Load Cell may not have the same wire color identifications as the original
load cell. It is necessary to identify the wires from the table below.
J3 has 5 solder pads with the following connections; GND, -EXE, -SIG, +SIG, +EXE.
TABLE 3-1. Load Cell Wire Color Identification
Spare Part Load Cell
Wire Color Identification
NV Models
GND
Green thick wire
-EXE
Black wire
-SIG
White wire
+SIG
Green wire
+EXE
Red wire
NVT Models
GND
Yellow wire
-EXE
Black wire
-SIG
White wire
+SIG
Green wire
+EXE
Red wire
NVT Approve Models
GND
Yellow wire
-EXE
Black wire
-SIG
Red wire
+SIG
White wire
+EXE
Green wire
Summary of Contents for Navigator Series
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