KERN & Sohn GmbH
Ziegelei 1
D-72336 Balingen
E-Mail: info@kern-sohn.com
Tel: +49-[0]7433-9933-0
Fax: +49-[0]7433-9933-149
Internet: www.kern-sohn.com
GB
Service Manual
Electronic Platform Scales
Page 2
KERN ECB / ECE
Version 2.0 4/2008
ECB/ECE-SH-e-0820
GB
KERN ECB / ECE
Version 2.0 4/2008
Service Manual
Electronic Platform Scales
Table of Contents
1 Features.......................................................................................................................3
2 Calibration Procedure (CAL) .....................................................................................3
3 Internal Calibration Procedure (Linearity Adjustment) ...........................................4
4 Display Segment Test .............................................................................................. 5
5 Functional Block Diagram / Description...................................................................6
5.1 Functional Block Diagram.....................................................................................................6
5.2 Function Description.............................................................................................................7
6 Trouble Shooting........................................................................................................ 8
7 To Replace PCB.......................................................................................................... 9
8 Schematics................................................................................................................ 10
9 Components Layout................................................................................................. 12
2 ECB/ECE-SH-e-0820
ECB/ECE-SH-e-0820 3
1 Features
• Zero weight function
• Negative value indication
• Low battery indicator
• Auto zero
• Display segments test function
• Auto off function in battery mode - enable/disable (only ECB)
• Overload protection
• Overload indication
• Digital span calibration
• Digital internal calibration
• Operated by 6 x AA size alkaline batteries
• Rechargeable battery as option
• Zero tracking - enable/disable (only ECB)
• Backlight - 3 modes (only ECB)
2 Calibration Procedure (CAL)
1. Turn scale on and allow the unit to acclimatize and stabilize for 10 minutes.
2. Press and hold the [Tare] key for approx. 3 seconds. Display will show [CAL] and then
the required calibration weight.
3. Gently place the correct calibration weight on the center on the weighing pan.
4. Wait until the display shows [ F] and then return to normal weighing mode
automatically.
5. Remove the calibration weight and 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 (Linearity Adjustment)
1. Remove the bottom cover under the PCB of the scale.
2. Connect J1 on the main board by soldering the pads together.
4 ECB/ECE-SH-e-0820
3. Place scale on a hard level surface. Turn scale on. Display shall show the internal
counts.
4. The internal counts shall fall in the range from 3 000 to 6 000. In case out of this
range, remove the four screws from the main board and lift it to see the rear side
of the main board.
5. Connect J9 left side or right side to increase or reduce the reading.
Connecting or disconnecting pads on J5, J6 or J7 can fine tune the reading.
ECB/ECE-SH-e-0820 5
6. If the internal counts are within the range, 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. Wait until display shows the next calibration
weight.
7. Repeat the above calibration procedure until display shows [ F].
8. Remove all weights from weighing pan and disconnect the power supply.
9. Disconnect J1 on the main board. Turn scale on and check the accuracy at different
weight.
10. Install the bottom cover of the scale.
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 approx.
2 seconds. Check for any missing segment.
5 Functional Block Diagram / Description
5.1 Functional Block Diagram
6 ECB/ECE-SH-e-0820
digital signal
analog
signal
Microprocessor
Power control /
Regulator &
Low battery
detector
Keyboard
A/D Converter
Battery (6xAA)
or
Adaptor
Amplifier
4 Load cells
(Sensor)
L C D
ECB/ECE-SH-e-0820 7
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, display, overload indication, low battery
indication, zero function, 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.
7. Keyboard
The keyboard provides on user interface. [On/Off] and [Tare] keys are employed to
operate the scale.
8 ECB/ECE-SH-e-0820
6 Trouble Shooting
Power on
↓
Full Segments?
If no display, check batteries / adaptor, keyboard / overlay, connection between
keyboard—main board, batteries / adaptor—main board.
If missing segments, check fixing of LCD, zebra connector under LCD.
↓
Display Zero?
If display [ LO], check battery>7.0V.
If display [ E] , check internal count.
↓
Proper readout?
If unstable reading, check weighing plate, overload stopper, load cell and
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.
ECB/ECE-SH-e-0820 9
7 To Replace PCB
1. Remove the bottom cover under the PCB of the scale.
2. Remove the four screws fixing the PCB and disconnect wires of keyboard, load cell
and battery/adaptor (backlight at ECB) from PCB. Replace a new PCB.
Connect wires of keyboard, load cell and battery/adaptor (backlight at ECB) to PCB
again. Assemble the screws fixing the PCB.
4. Perform internal calibration as described in section 3.
5. Assemble the bottom cover of the scale.
6. Check accuracy of scale at different weight.
ECB 10K10 ECB 20K20 ECB 50K50
weight tolerance weight tolerance weight tolerance
2.00 kg 0.02 kg 5.00 kg 0.04 kg 10.00 kg 0.10 kg
5.00 kg 0.02 kg 10.00 kg 0.04 kg 20.00 kg 0.10 kg
7.00 kg 0.02 kg 15.00 kg 0.04 kg 30.00 kg 0.10 kg
10.00 kg 0.02 kg 20.00 kg 0.04 kg 40.00 kg 0.10 kg
50.00 kg
0.10 kg
ECE 10K10 ECE 20K20 ECE 50K50
weight tolerance weight tolerance weight tolerance
2.00 kg 0.02 kg 5.00 kg 0.04 kg 10.00 kg 0.10 kg
5.00 kg 0.02 kg 10.00 kg 0.04 kg 20.00 kg 0.10 kg
7.00 kg 0.02 kg 15.00 kg 0.04 kg 30.00 kg 0.10 kg
10.00 kg 0.02 kg 20.00 kg 0.04 kg 40.00 kg 0.10 kg
50.00 kg
0.10 kg
7. Check other functions, such as Tare, Off and Auto-Off.
8 Schematics
10 ECB/ECE-SH-e-0820
ECB/ECE-SH-e-0820 11
9 Components Layout
12 ECB/ECE-SH-e-0820
ECB/ECE-SH-e-0820 13
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