Determine The Problem; Check The Load Cell; Checking The Different Voltages - KERN MWA NM Series Service Manual

9.3 Determine the Problem

Determine whether the problem is in the PCB or the Load Cell
 Disconnect the power supply from the scale, and disconnect the load cell
connection from the PCB
 Reapply power and test the PCB
 If problem goes away, its source is probably in the Load cell. Check the wiring,
connecter, load cell and mechanical components of the load cell.
 If problem persists, its source is probably in the PCB. Check the PCB
voltages, connecters, cables and function programs

9.4 Check the Load cell

 Remove power from the system, and disconnect the PCB from the Load cell
 Check the moisture, or foreign material inside.
 Make sure all leads are connected and correctly.
 Check load cell for proper input and output resistances
Load Cell Connections
Measuring Points
Red (+ Exc) to White ( –Exc)
Green (+Sig) to Black ( –Sig)

9.5 Checking the different Voltages

f the problem is in the PCB, use a multimeter to check the following voltages
I
AC Power
Check the AC power socket out put voltage.
Adaptor Voltage
Check the adaptor output cable connecter voltage
Compare the value with the name plate on the scale
PCB Input Voltage
Check the PCB input power connecter voltage
Voltage must be minimum 9VDC in to the pin AD+
Check Battery Voltage and Charging Voltage
MWA_NM-SH-e-1810
Signal + Green
Supply + Red
Signal - Black
Supply - White
Shield
Resistance
420 ±20Ω
350Ω ±5Ω
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