KERN TEE 150-1 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
GB Service Manual
Electronic Pocket Balance Page 2
KERN TEE
Version 1.0 4/2008
TEE-SH-e-0810

GB KERN TEE
Version 1.0 4/2008
Service Manual
Electronic Pocket Balance
2 TEE-SH-e-0810
Table of Contents
1Features.......................................................................................................................3
2Calibration Procedure (CAL) .....................................................................................3
3Internal Calibration Procedure ..................................................................................3
4Functional Block Diagram / Description...................................................................4
4.1 Functional Block Diagram.....................................................................................................4
4.2 Function Description.............................................................................................................5
5Trouble Shooting........................................................................................................6
6To Replace PCB..........................................................................................................7
7To Replace Load Cell Assembly................................................................................7
8Schematics..................................................................................................................8
9Components Layout...................................................................................................9

TEE-SH-e-0810 3
1 Features
•Full Tare
•Display segment test function
•Negative value indication
•Stable indicator
•Low battery indicator
•Auto zero
•Auto off function
•Overload protection
•Two types of Digital Auto Calibration
•Solder pads to prevent end-user internal calibration
•Operated by 2 x AA alkaline batteries
2 Calibration Procedure (CAL)
1. Turn scale on and allow the unit to acclimatize and stabilize for 1 minute.
2. Press and hold the [Light/Cal] 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 display shows [ F] then turn off.
In case [ E] is displayed instead of [ F], this indicates a calibration
procedure error, unstable or wrong calibration weight applied for calibration.
Turn the scale off and on again and repeat the procedure.
3 Internal Calibration Procedure
1. Remove two screws of the rear housing and open it.
2. Connect J1 on the main board by soldering the pads together.
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 5 000. In case out of this
range, connect J8 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.
5. Press [On/Zero/Off] key once. Display will show [CAL] and then the required calibration
weight. Place the corresponding calibration weight on the center of the weighing pan
and wait until display shows [ F] and then turn off.
6. Disconnect J1. Calibration completed.
7. Turn scale on and check the accuracy at different weight.
8. Install rear housing of the scale.
In case [CAL E] is display instead of [CAL 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 Functional Block Diagram / Description
4.1 Functional Block Diagram
4 TEE-SH-e-0810
digital signal
analog
signal
Microprocessor
Power control /
Regulator &
Low battery
detector
Keyboard
A/D Converter
Battery
2 x AAA
Load cell
(Sensor)
Amplifier
L C D

TEE-SH-e-0810 5
4.2 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, 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.
7. Keyboard
The keyboard provides on user interface. [On/Zero/Off] and [Light/Cal] keys are
employed to operate the scale.

6 TEE-SH-e-0810
5 Trouble Shooting
Power on
↓
Full Segments?
If no display, check battery, connection between battery—main board.
If missing segments, check fixing of LCD frame, zebra connector under LCD.
↓
Display Zero?
If display [LO], check battery >2.5V.
If display [ E] , check internal count.
↓
Proper readout?
If unstable reading, check load cell and environmental conditions.
↓
Correct reading?
If not accurate, perform internal calibration.
If cannot reach full capacity, check load cell and internal zero point.
If always zero, check internal zero point. Internal calibration if necessary.
↓
Normal operation.

TEE-SH-e-0810 7
6 To Replace PCB
1. Disassemble rear housing of scale.
2. Disconnect wires to PCB. Replace a new PCB. Connect wires to PCB again.
3. Perform internal calibration as described in section 3.
4. Assemble rear housing of scale.
5. Check accuracy of scale at different weight.
TEE 150-1
weight Tolorance
50g 0.2g
100g 0.2g
150g 0.2g
6. Check other functions, such as Tare, Backlight and Auto-Off.
7 To Replace Load Cell Assembly
1. Disassemble rear housing of scale.
2. Disassemble screws fixing the load cell.
3. Disconnect wires to PCB. Replace the load cell with a new one.
Assemble screws fixing the load cell. Connect wires to PCB.
4. Perform internal calibration as described in section 3.
5. Assemble rear housing of scale.
6. Check accuracy of scale at different weight.
TEE 150-1
weight Tolorance
50g 0.2g
100g 0.2g
150g 0.2g
7. Check other functions, such as Tare, Backlight and Auto-Off.

8 Schematics
TEE 150-1
8 TEE-SH-e-0810

9 Components Layout
TEE-SH-e-0810 9