KERN FCE 3K1 User 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
Compact balances
KERN FCE
Version 1.0
4/2009
GB
FCE-SH-e-0910

GB KERN FCE
Version 1.0 4/2009
Service manual
Compact balances
2 FCE-SH-e-0910
Table of Contents
1Basic Information ___________________________________________________ 3
2Digital Auto Calibration Procedure _____________________________________ 3
3Internal Calibration Procedure________________________________________ 4
4Display Segment Test_______________________________________________ 4
5Functional Block Diagram / Description_________________________________ 5
5.1 Functional Block Diagram _________________________________________________ 5
5.2 Function Description _____________________________________________________ 6
6Trouble Shooting ___________________________________________________ 7
7To Replace PCB ____________________________________________________ 8
8To Replace Load Cell Assembly _______________________________________ 9
9Schematics _______________________________________________________ 10
10 Components Layout ________________________________________________ 12

FCE-SH-e-0910 3
1 Basic Information
Grundlegende Hinweise
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.
Das Gerät darf nur von geschultem oder beruflich ausgebildetem
Fachpersonal (z. B. eichrechtlich anerkannter Instandsetzer) repariert werden.
Die Serviceanleitung ist bindend für Reparaturen.
Das Gerät muss nach erfolgter Reparatur wieder in den Originalzustand
zurückversetzt werden.
Es dürfen nur Originalersatzteile verwendet werden.
2 Digital Auto Calibration Procedure
1. Turn balance on and allow the unit to acclimatize and stabilize for 10 minutes.
2. Press and hold the [TARE] key until the display shows CAL and a weight reading.
The weight reading indicates the correct weight that must be placed on the
weighing pan.
3. Gently place the correct calibration weight on the center on the weighing pan.
4. The display will now show [ F ] and then return to normal operating mode. The
calibration is complete when the display correctly shows the weight that is placed on
the weighing pan while the display has stabilized.
5. Remove the calibration weight and if necessary press the [TARE] key to reset the zero
point.
In case [ E ] is displayed instead of [ F ], this indicates a calibration
procedure error. Turn the scale off and then on and repeat the procedure.

3 Internal Calibration Procedure
1. Remove the top housing of the scale.
2. Connect J1’ on the main board 5052-094108 by soldering the pads together (Fig.1).
3. Place scale on a hard level surface. With weighing pan installed, turn balance on.
Display shall show the internal counts.
4. The internal counts shall fall in the range from 2 000 to 5 000.
In case out of this range, connect J9 left side or right side to increase or reduce the
reading (Fig.1).
Connecting or disconnecting pads on J5, J6 or J7 can fine tune the reading (Fig.1).
5. Press [ON/OFF] key once. Display will show [ CAL ] and then the required calibration
weight. Place the corresponding calibration weight on the center of the weighing plate.
6. The display will now show [ F ] and then return to internal counts reading.
7. Remove all weights from weighing pan and plug-off the power supply.
8. Disconnect J1’.
9. Install the top housing of scale.
J1’
Fig.1
In case [ E ] is display instead of [ F ], this indicates a calibration procedure error,
or wrong weight applied for calibration.
Turn the scale off and then on and repeat the procedure.
4 Display Segment Test
Whenever the scale is power on, all segments of the LCD will be turn on for 2 seconds.
Check for any missing segment.
4 FCE-SH-e-0910

5 Functional Block Diagram / Description
5.1 Functional Block Diagram
FCE-SH-e-0910 5
digital signal
analog
signal
Microprocessor
Power control /
Regulator &
Low battery
detector
Keyboard
L C D
A/D Converter
9V Battery
or
Adaptor
Load cell
(Sensor)
Amplifier

6 FCE-SH-e-0910
5.2 Function Description
1. Load cell
This is the heart of the whole system. The load cell itself is arranged as a bridge.
The resistance change of the bridge elements is proportional to the load applied on
the load cell. Therefore, the output of the load cell is an analog signal, which is
proportional to the load applied on the scale.
2. Amplifier
The analog signal from the load cell is very small, of the order of micro-volt.
Hence, a linear and stable amplifier is applied to amplify the analog signal to an
appropriate level.
3. A/D Converter
In order for the analog signal can be input to the microprocessor, this part converts the
analog signal to its digital equivalent. The operation of the analog to digital converter
is using a SIGMA DELTA technique and under the control of the microprocessor.
4. Microprocessor
The microprocessor control all the functions of the scale, such as auto zero,
A/D conversion, timings, weight calculation, and display, overload indication,
low battery indication, tare, etc….
5. Display
This is the part where the weight is shown out on the LCD display in digital form.
The whole display is driven by the microprocessor.
6. Power Regulator and Low Battery Detector
This part contains the ON/OFF power control. In order for the external power can be
used by other parts of the scale, a regulator is used to regulate the supply.
A low battery detector is employed to make sure that the power supply is strong
enough for normal operation of the scale. If rechargeable battery is installed,
it can be charged up by the charging circuit.
7. Keyboard
The keyboard provides on user interface. [On/Off] and [Tare] keys are employed
to operate the scale.

FCE-SH-e-0910 7
6 Trouble Shooting
Power on
↓
Full Segments?
If no display, check battery /adaptor; connection between keyboard—main
board, battery/adaptor—main board.
If missing segments, check fixing of LCD frame, zebra connector under LCD.
↓
Display Zero?
If display [LO], check battery>7.5v, adaptor>9v.
If display [ E] , check internal count.
↓
Proper readout?
If unstable reading, check weighing plate, overload stopper, load cell and wires,
environmental conditions and stable table.
↓
Correct reading?
If not accurate, perform internal calibration.
If cannot reach full capacity, check weighing plate, overload stopper, load cell
and internal zero point.
If always zero, check internal zero point. Internal calibration if necessary.
↓
Normal operation.

8 FCE-SH-e-0910
7 To Replace PCB
1. Disassemble top housing of scale.
2. Disconnect connections to keyboard, loadcell and battery/adaptor from the PCB.
Replace a new PCB. Connect connections from PCB to keyboard, loadcell and
battery/adaptor again.
3. Assemble the top housing.
4. Perform internal calibration as described in section 3.
5. Check accuracy of scale at different weight.
FCE 3K1 FCE 6K2 FCE 15K5
weight tol. weight tol. weight tol.
1000g 2g 2000g 4g 5000g 10g
2000g 2g 4000g 4g 10000g 10g
3000g 2g 6000g 4g 15000g 10g
FCE 30K10 FCE 30K10L FCE 60K20
weight tol. weight tol. weight tol.
10.00kg 0.02kg 10.00kg 0.02kg 20.00kg 0.04kg
20.00kg 0.02kg 20.00kg 0.02kg 40.00kg 0.04kg
30.00kg 0.02kg 30.00kg 0.02kg 60.00kg 0.04kg
6. Check other functions, such as Tare, Off and Auto-Off.

FCE-SH-e-0910 9
8 To Replace Load Cell Assembly
1. Disassemble top housing of scale.
2. Disconnect loadcell wires from main PCB. Remove the screws fixing the bottom plate
of the load cell assembly. Replace the load cell with a new one.
Connect load cell wires and fix the screws.
3. Put 110% full capacity loading onto weight stand of scale. Adjust the overload screws
on the weight stand until they just not touch the bottom plate.
4. Assemble the top housing.
5. Perform internal calibration as described in section 3.
6. Check accuracy of scale at different weight.
FCE 3K1 FCE 6K2 FCE 15K5
weight tol. weight tol. weight tol.
1000g 2g 2000g 4g 5000g 10g
2000g 2g 4000g 4g 10000g 10g
3000g 2g 6000g 4g 15000g 10g
FCE 30K10 FCE 30K10L FCE 60K20
weight tol. weight tol. weight tol.
10.00kg 0.02kg 10.00kg 0.02kg 20.00kg 0.04kg
20.00kg 0.02kg 20.00kg 0.02kg 40.00kg 0.04kg
30.00kg 0.02kg 30.00kg 0.02kg 60.00kg 0.04kg
7. Check other functions, such as Tare, Off and Auto-Off.

9 Schematics
10 FCE-SH-e-0910

FCE-SH-e-0910 11

10 Components Layout
12 FCE-SH-e-0910

FCE-SH-e-0910 13