KERN MWB series Service Manual

KERN & Sohn GmbH

Ziegelei 1
D-72336 Balingen
E-Mail: [e-mail]

Tel: +49-[0]7433- 9933-0
Fax: +49-[0]7433-9933-149
Internet: www.kern-sohn.com

Service Manual
Wheelchair scale

KERN MWB

Version 1.0

03/2018
GB

Importør:
Impex Produkter AS
Gamle Drammensvei 107
1363 Høvik
www.impex.no
[e-mail]
Tel.: [phone]

MWB-SH-e-1810

GB

KERN MWB
Wheelchair scale

Version 1.0 04/2018

Service manual

Content

1 Basic Information ............................................................................................... 4

2 Introdution .......................................................................................................... 4

3 Appliance overview............................................................................................ 5

3.1 Details ....................................................................................................................................6

3.2 Overview display ...................................................................................................................7

3.3 Overview Keyboard ...............................................................................................................8

4 Basic Information (General) .............................................................................. 9

4.1 Proper use ................................................................ ................................ .............................9

4.2 Improper Use .........................................................................................................................9

4.3 Warranty ................................................................................................................................9

4.4 Monitoring of Test Resources ..............................................................................................9

5 Basic Safety Precautions ................................................................................ 10

5.1 Pay attention to the instructions in the Operation Manual ................................................ 10

6 Transport and storage ..................................................................................... 10

6.1 Testing upon acceptance .................................................................................................... 10

6.2 Packaging / return transport ............................................................................................... 10

7 Unpacking, Setup and Commissioning .......................................................... 11

7.1 Place of installation / place of operation ............................................................................ 11

7.2 Unpacking ............................................................................................................................ 11

7.3 Scope of delivery ................................................................................................................. 11

7.4 Levelling .............................................................................................................................. 11

8 Menu.................................................................................................................. 12

8.1 Navigation in the menu ....................................................................................................... 12

8.2 Menu overview..................................................................................................................... 12

9 Error Messages ................................................................................................ 14

10 Servicing, maintenance, disposal ............................................................... 15

10.1 Cleaning ............................................................................................................................... 15

10.2 Cleaning / disinfecting ........................................................................................................ 15

10.3 Servicing, maintenance ....................................................................................................... 15

10.4 Disposal ................................................................ ............................................................... 15

11 Instant help.................................................................................................... 15

12 Adjustment .................................................................................................... 17

13 MAINTENENCE ............................................................................................. 18

13.1 General ................................................................................................................................ 18

13.2 Cleaning ............................................................................................................................... 18

13.3 Determine the Problem ................................................................ ....................................... 18

13.4 Check the Load cell ............................................................................................................. 18

2 MWB-SH-e-1810.docx

13.5 Load Cell Connections ........................................................................................................ 19

13.6 Check PCB Voltages ........................................................................................................... 20

13.7 PCB Input Voltage ............................................................................................................... 20

13.8 Check Battery Voltage......................................................................................................... 20

13.9 Replace Main Board ............................................................................................................ 21

13.10 Replace Battery ............................................................................................................... 21

14 Drawing.......................................................................................................... 22

15 Schematic ................................ ...................................................................... 23

MWB-SH-e-1810.docx 3

1 Basic Information

The device must be repaired only by trained specialist staff or personnel with professional
formation (such as a repair-specialist accredited by law concerning verification). The service
manual is obligatory for repair work. After repair, original conditions of the device have to be
restored. Only original spare parts should be used.

Instructions about conformity-evaluated scales:

Repair must be carried only at 100% compliance with the type approval. A violation of this
specification will result in a loss of the type approval! After successful repair the balance will
have to be reverified before it can be used again in a statutorily regulated field.

Detailed instructions about conformity-evaluated scales:

Repair must be carried only at 100% compliance with the type approval. A violation of this
specification will result in a loss of the type approval!

After successful repair the balance will have to be reverified before it can be used again in a
statutorily regulated field.

2 Introdution

This service manual covers the MWB series and is edited for the authorized servicing
personnel.
Note all rights are reserved. Copying any part of this manual is prohibited without our
permission.

In this lineup it is an eco product, Therefore, it is not intended to represent the repair manual
in detail, since the construction of the balance is very simple. It is therefore only referring to
the list of related to disposal spare parts.

4 MWB-SH-e-1810.docx

3 Appliance overview

Bubble level and handle (2x)

Conveyor roller (2x)

1. Cover of weighing cell feet

2. Weighing surface

3. Bubble level

4. Hand grip

5. Connection cable

6. Display Unit

MWB-SH-e-1810.docx 5

3.1 Details

Display unit rear side

1

Battery compartment

2

Connecting cable

display unit - platform

6 MWB-SH-e-1810.docx

3.2 Overview display

Display

Designation

Description

GROSS

Gross weight display

Lights up during indication of the gross
weight

NET

Net weight display

Lights up during indication of the net weight
Illuminated after weighing scale was tared

ZERO

Zeroing display

Should the balance not display exactly zero
despite empty scale pan, press the button.
Your balance will be set to zero after a short
standby time.

STABLE

Stability display

Scales are in a steady state

BMI

Body Mass Index

Is actively displayed during active BMI
function

HOLD

HOLD function

Is displayed with active hold function

Battery symbol
Lights when the voltage drops below the

prescribed minimum.

Lights when the battery capacity is almost
exhausted.

Lights when the battery is fully charged.

MWB-SH-e-1810.docx 7

3.3 Overview Keyboard

Button

Designation

Function

ON/OFF button

Turn on/off

HOLD button

Hold function

BMI key

Calculation of the Body Mass Index

In menu:

 Confirm selection

For numeric entry:

 Confirm numerical value

Function key

In menu:

 Call up menu
 Select menu items

For numeric entry:

 Increase numerical value

Zero setting key

Weighing scale will be reset to „0.0“

For numeric entry:

 Change decimal place

TARE key

Tare balance

8 MWB-SH-e-1810.docx

4 Basic Information (General)

4.1 Proper use

This weighing scale is designed for determining the weight of a person whilst standing or
sitting.
On multifunctional weighing scales, the weighed person should carefully step onto the center
of the weighing platform and remain standing without moving. If weighed with a wheelchair,
the wheelchair should remain in the center of the weighing plate.
As soon as a stable weighing value is reached the weighing value can be read.
The weighing scale is designed for continuous duty.

4.2 Improper Use

Do not use these scales for dynamic weighing processes.
Do not leave permanent load on the weighing plate. This may damage the measuring
system.
Impacts and overloading exceeding the stated maximum load (max) of the weighing plate,
minus a possibly existing tare load, must be strictly avoided. This could cause damage to the
balance.
Never operate balance in explosive environment. The serial version is not explosion
protected. It should be noted that a flammable mixture of anesthetics and oxygen or laughing
gas may occur.
The structure of the balance may not be modified. This may lead to incorrect weighing
results, safety-related faults and destruction of the balance.
The balance may only be used according to the described conditions. Other areas of use
must be released by KERN in writing.
The balance cannot be used to determine a body weight in practice of medicine.

4.3 Warranty

Warranty claims shall be voided in case

 Our conditions in the operation manual are ignored
 The appliance is used outside the described uses

 Modification or opening of appliances
 Mechanical damage and damage caused by media, liquids,

 Natural wear and tear
 The appliance is improperly set up or incorrectly electrically connected

 The measuring system is overloaded
 Dropping of scales

4.4 Monitoring of Test Resources

In the framework of quality assurance the measuring-related weighing properties of the
balances and, if applicable, the testing weight, must be checked regularly. The responsible
user must define a suitable interval as well as type and scope of this test. Information is

available on KERN’s home page (www.kern-sohn.com) with regard to the monitoring of

balance test substances and the test weights required for this. In KERN’s accredited DKD

calibration laboratory test weights and balances may be calibrated (return to the national
standard) fast and at moderate cost.

MWB-SH-e-1810.docx 9

5 Basic Safety Precautions

5.1 Pay attention to the instructions in the Operation Manual

 Carefully read this operation manual before setup

and commissioning, even if you are already familiar
with KERN balances.

6 Transport and storage

6.1 Testing upon acceptance

When receiving the appliance, please check packaging immediately, and the appliance itself
when unpacking for possible visible damage.

6.2 Packaging / return transport

 Keep all parts of the original packaging for a possibly required return.
 Only use original packaging for returning.
 Prior to dispatch disconnect all cables and remove loose/mobile parts.
 Reattach possibly supplied transport securing devices.
 Secure all parts against shifting and damage.

10 MWB-SH-e-1810.docx

7 Unpacking, Setup and Commissioning

7.1 Place of installation / place of operation

The balances are designed in a way that reliable weighing results are achieved in common
conditions of use. You will work accurately and fast, if you select the right location for your
balance.

On the installation site observe the following:

 Place scales on a stable, even surface
 Avoid extreme heat as well as temperature fluctuation caused by installing next to a

radiator or in the direct sunlight;

 Protect the balance against direct draughts due to open windows and doors;
 Avoid jarring during weighing;
 Protect the balance against high humidity, vapours and dust;
 Do not expose the device to extreme dampness for longer periods of time. Non-permitted

condensation (condensation of air humidity on the appliance) may occur if a cold
appliance is taken to a considerably warmer environment. In this case, acclimatize the
disconnected appliance for ca. 2 hours at room temperature.

 Avoid static charge of the balance and of the person to be weighed.
 Avoid contact with water.

Major display deviations (incorrect weighing results) may be experienced should
electromagnetic fields (e.g. due to mobile phones or radio equipment), static electricity
accumulations or instable power supply occur. In that case, the location must be changed.

7.2 Unpacking

Remove the individual components of the balance or the complete balance from the
packaging with care and install at the intended location. When using the power pack, ensure
that the power cable does not produce a risk of stumbling.

 Balance, completely assembled
 Operating manual

 Level balance with foot screws until the air bubble of the water

balance is in the prescribed circle.

 Check levelling regularly.

7.3 Scope of delivery

7.4 Levelling

MWB-SH-e-1810.docx 11

8 Menu

Call up menu

 In weighing mode, press and the first function [F1

oFF] will be displayed.

Select function

 With help of , the individual functions can be

selected one after the other.

Change settings

 Confirm selected function by . The current setting

will be displayed.

 Select desired setting by and confirm with ,

the balance returns to the menu.

Exit menu/
Return to weighing

mode

 Press , the balance will return to weighing mode.

Function

Settings

Description

Adjustment

Adjustment

d 0, d 0.0, d 0.00,
d 0.000, d 0.0000

Capacity

Automatic cutout
Auto Off

oFF 3

Automatic shutdown after 3 min.

oFF 5

Automatic shutdown after 5 min.

oFF 15

Automatic shutdown after 15 min.

8.1 Navigation in the menu

8.2 Menu overview

12 MWB-SH-e-1810.docx

Gravity

Gravity
not documented

MWB-SH-e-1810.docx 13

9 Error Messages

Display

Description

Zero range exceeded

(on start-up or when pressing the key)

 Load on weighing pan
 Excess load, during zero setting of weighing scale
 Incorrect adjusting process
 Fault on load cell

Value outside the A/D converter range

 Damaged weighing cell
 Damaged electronics

Unable to initialize zero point

 Measuring cell defective / overloaded
 Object on weighing pan / contact
 Transport safety device has not been removed
 Main board defective

OL or --------

Overload

 Unload, switch off and adjust the balance

------or „0“

Underload

 Unload, switch off and adjust the balance

Should other error messages occur, switch balance off and then on again. If the error
message remains inform manufacturer.

14 MWB-SH-e-1810.docx

10 Servicing, maintenance, disposal

Before any maintenance, cleaning and repair work disconnect the appliance
from the operating voltage.

In case of a fault in the program sequence, the balance should be shortly switched off.
The weighing process must then be restarted from the beginning.

Failure:

Possible causes:

The displayed weight does
not glow.

 The balance is not switched on.
 The mains supply connection has been interrupted

(mains cable not plugged in/faulty).

 Power supply interrupted.
 Battery inserted incorrectly or empty.
 No battery inserted.

The displayed weight is
permanently changing

 Draught/air movement
 Table/floor vibrations
 The seating surface is in contact with foreign bodies or

is not correctly positioned.

 Electromagnetic fields / static charging (choose different

location/switch off interfering device if possible)

10.1 Cleaning

10.2 Cleaning / disinfecting

Clean weighing platform (such as seat pan) as well as casing with household detergents or
commercially available disinfectants, e.g. 70% isopropanol. We recommend a disinfectant
suitable for wiping disinfection. Please follow manufacturer’s instructions.

Do not use abrasive or aggressive cleaners such as spirits or alcohol or similar as they might
damage the high-quality surface.

10.3 Servicing, maintenance

The appliance may only be opened by trained service technicians who are authorized by
KERN.
Disconnect the scales before opening.

10.4 Disposal

Disposal of packaging and appliance must be carried out by operator according to valid
national or regional law of the location where the appliance is used.

11 Instant help

MWB-SH-e-1810.docx 15

The weighing result is
obviously incorrect

 The display of the balance is not at zero.
 Adjustment is no longer correct.
 Great fluctuations in temperature.
 The balance is on an uneven surface.
 Electromagnetic fields / static charging (choose different

location/switch off interfering device if possible)

Should other error messages occur, switch balance off and then on again. If the error
message remains inform manufacturer.

16 MWB-SH-e-1810.docx

12 Adjustment

 Prepare the required adjustment weight. The adjustment weight to be applied

depends on the capacity of a weighing scale, see chap. 1.
Carry out adjustment as closely as possible to admissible maximum load of
weighing scale. Info about test weights can be found on the Internet at:
http://www.kern-sohn.com.

 Observe stable environmental conditions. For warm-up time required for

stabilization

 Switch-on balance by and during the selftest press .[F0

CAL] is displayed.

 Press , [CAL] will be displayed

 Press again, [ULOAD] will be displayed.

 Wait for stability display, then press , an adjustment weight

will be displayed. The right digit flashes. Or confirm value with

, or enter a new value with the keys and confirm

by .

 Place a corresponding adjustment weight, wait for stability display

and confirm by .

 [--------] will be shortly displayed, followed by [F0 CAL]

The adjustment is now finished. Should an error occur, repeat
adjustment.

As the acceleration value due to gravity is not the same at every location on earth, each
display unit with connected weighing plate must be coordinated - in compliance with the
underlying physical weighing principle - to the existing acceleration due to gravity at its place
of location (only if the weighing system has not already been adjusted to the location in the
factory). This adjustment process must be carried out for the first commissioning, after each
change of location as well as in case of fluctuating environment temperature. To receive
accurate measuring values it is also recommended to adjust the display unit periodically in
weighing operation.

Procedure:

MWB-SH-e-1810.docx 17

13 MAINTENENCE

13.1 General

If the scale does not operate properly, find out the problem as possible. Determine
whether the problem is constant or alternate. Be aware that problems can be caused by
mechanical or electrical influences.

Check the following.

 Water


Corrosive materials



Vibrations or temperature or wind



Physical damage

Check the scale cables for damage, and check all connections and connecters for any
loose contact or incorrect connection

13.2 Cleaning

 Disconnect the power before cleaning.


Use a cloth with mild suds and light cleaning agents.



Make sure that fluid not able to get into the device.



Use a clean and soft cloth for rub off.

13.3 Determine the Problem

Determine whether the problem is in the PCB or the Load Cell

 Remove power from the system, and disconnect the load cell connection from

the PCB



Connect the PCB to a load cell simulator



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

13.4 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

18 MWB-SH-e-1810.docx

13.5 Load Cell Connections

Measuring Points

Resistance

Red (+ Exc) to White ( –Exc)

420 ±20Ω

Green (+Sig) to Black ( –Sig)

350Ω ±5Ω

Signal + Green

Supply + Red

Signal - Black

Supply ­Shield

Whit

e

Load cell connection for the 4 load
cell’s.

RED --------- EXE +
WHITE------- SIG –
GREEN----- SIG +
BLACK------ EXE ­YELLOW--- SHIELD

Connection for the indicator
RED --------- EXE +

Empty------- SEN +
GREEN----- SIG +
BLACK------ SHIELD
BLUE-------- SIG –
Empty------- SEN –
YELLOW--- EXE –

MWB-SH-e-1810.docx 19

13.6 Check PCB Voltages

If the problem is in the PCB, use a multimeter to check the following voltages

13.7 PCB Input Voltage

Check the PCB input power connecter voltage

Voltage must be minimum 9VDC in to the pin AD+

13.8 Check Battery Voltage

Check the Battery Voltage

The battery voltage below the 1.5VDC, replace the battery and install new

1.5V battery.

20 MWB-SH-e-1810.docx

13.9 Replace Main Board

Release 4 pcs screw from bottom of the

scale by using cross screw driver.

Open the top cover, the main board lie on top

cover, use cross screw driver loose 4 screw
for main board, pull out all connector on the
main board, then you can bring out main
board carefully.

Install the new main board, plug all connector at last,After check anything，

try to turn on the power，if anything is OK，close the top cover，replace main
board completely.

13.10 Replace Battery

Open battery compartment cover

Remove the dry battery

Insert new batteries ,Lock the
battery cover again.

MWB-SH-e-1810.docx 21

14 Drawing

22 MWB-SH-e-1810.docx

15 Schematic

MWB-SH-e-1810.docx 23