KERN & Sohn GmbH
D-72322 Balingen-Frommern
Postbox 4052
E-Mail: info@kern-sohn.de
Tel: 0049-[0]7433- 9933-0
Fax: 0049-[0]7433-9933-149
Internet: www.kern-sohn.de
E
Service Manual
Electronic Precision Balances
Page 2
KERN DE
version 1.1 06/01
DE-SH-e-0111
E
KERN DE
version 1.1 06/01
Service Manual
Electronic Precision Balances
1 INTRODUCTION .....................................................................................................3
1.1 Features............................................................................................................3
1.2 Digital auto adjusting procedure....................................................................3
1.3 Internal adjusting procedure ..........................................................................4
1.4 Display segment test.......................................................................................4
2 FUNCTIONAL BLOCK DIAGRAM / DESCRIPTION ..............................................5
2.1 Functional block diagram ...............................................................................5
2.2 Function description .......................................................................................6
3 TROUBLESHOOTING ............................................................................................7
4 REPLACEMENT OF PCBA ....................................................................................8
4.1 Replacement of analogue PCBA ....................................................................8
4.2 Replacement of display PCBA .......................................................................8
5 SCHEMATICS.........................................................................................................9
6 SPARE PARTS LIST ............................................................................................13
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1 Introduction
1.1 Features
• Full Tare
• Memory function with indicator
• Stable indicator
• Negative value indication
• Two types of Digital Auto Adjusting
• Solder Pads to prevent end-user internal adjusting
• Low battery indicator
• Auto off function (battery mode only)
• AC adaptable
• Display segment test function
• Overload indication / protection
1.2 Digital auto adjusting procedure
1. Turn balance on and allow the unit to acclimatise and stabilise for two minutes.
2. Press and hold the MODE key until the display shows a flashing weight reading.
The flashing weight reading indicates the correct weight that must be placed on the
platform.
3. With the display still flashing, press the OFF key. The display will now show CAL 0.
Then gently place the correct adjusting weight on the centre of the platform.
4. The display will now show CAL F and then return to normal operating mode. The
adjusting is complete when the display correctly shows the weight that is placed on
the platform and the display has stabilised.
5. Remove the adjusting weight and press the TARE key to reset the zero point..
In case CAL E is display instead of CAL F, this indicates an adjusting procedure error.
Turn the balance off and then on and repeat the procedure.
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1.3 Internal adjusting procedure
1. Remove the bottom housing of the remote display box.
2. Connect J2 on the display board (by soldering).
3. With platform empty, turn the balance on. The display should now zero with the unit
indicator on.
4. Press the MODE key once. The display should show the internal count. The
reading should fall in the range from 9.500 to 10.000. In case out of this range,
adjust VR 1 located on the balance board inside the platform. Connecting pads on
J1 located underneath R4 on the solder side of the balance board can further
increase or reduce the reading.
5. Press the OFF key once. The display will show CAL 0 and then the required
adjusting weight. Place the corresponding adjusting weight in the centre of the
platform.
6. The display will now show CAL L and then the next adjusting weight. Place the
corresponding adjusting weight on the platform. Repeat this step until the display
shows CAL F.
7. Disconnect J2 on the display board. The adjusting is completed. Reset the zero
point and check the accuracy at different weights.
8. Install the bottom housing of the remote display box.
In case CAL E is displayed instead of CAL F, this indicates an adjusting procedure
error, or a wrong weight has been applied for adjusting. Turn the balance off and then
on and repeat the procedure.
1.4 Display segment test
Whenever the balance is turned on, all segments of the LCD will appear for 2 seconds.
Check for any missing segment.
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2 Functional block diagram / description
2.1 Functional block diagram
LC D
Keyboa rd
9 V B a tte ry
or
Adapter
Micro-
processor
Po w er control /
Re g ulator &
Lo w b a tte ry
detector
Lo a d c e ll
(S e n so r)
Am plifier
A/D C onverte r
Analogue signal
Digita l si gnal
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2.2 Function description
1. Load cell
This is the heart of the whole system. Four load cells, located in the four corners of the
platform, are arranged as a bridge. The resistance change of the bridge elements is
proportional to the load applied on the load cells. Therefore the output of the load cells
is an analogue signal, which is proportional to the load applied on the platform.
2. Amplifier
The analogue 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 analogue signal to an appropriate
level.
3. A/D Converter
In order for the analogue signal can be input to the microprocessor, this part converts
the analogue signal to its digital equivalent. The operation of the analogue to digital
converter is using a VOLTAGE TO FREQUENCY technique and is controlled by the
microprocessor.
4. Microprocessor
The microprocessor controls all the functions of the balance, such as auto zero, A/D
conversion, timings, weight calculation and display, overload indication, low battery
indication, memory / tare 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 balance, 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 balance.
7. Keyboard
The keyboard provides the user interface. ON/MEMORY, MODE, TARE and OFF
keys are employed to operate the balance.
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3 Troubleshooting
Turn the balance on
Ð
Full segments on the display ?
If no display, check battery / adapter; connection between keyboard – display
board, battery / adapter – display board.
If some segments are missing, check fixing of the LCD frame, the zebra
connector underneath the LCD.
Ð
Display zero ?
If display is LO, check the battery > 7,5 V, adapter > 9 V.
If display is E, check the internal count.
Ð
Proper readout ?
If the reading is unstable, check the platform, all stoppers and loadcells.
Ð
Is the reading correct ?
If the reading is not accurate, perform an internal adjusting.
If the balance cannot reach its full capacity, check the platform, all stoppers, load
cells and the internal zero point.
If zero is always displayed, check the internal zero point. Perform an internal
adjusting if necessary.
Ð
Normal operation.
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4 Replacement of PCBA
4.1 Replacement of analogue PCBA
1. Disassemble the stainless cover and the metal top housing from the platform.
2. Disconnect PL1 and PL2 from the analogue PCBA. Replace it by a new PCBA.
Connect PL1 and PL2 again. Assemble the ground wire with a screw.
3. Assemble the metal top housing and the stainless steel cover.
4. Perform an internal adjusting as described in section 1.
5. Check the accuracy of the balance at different weights.
DE6K2 DE15K5 DE30K10 DE60K20 DE150K50 DE300K100
weight
(kg)
+/- weight
(kg)
+/- weight
(kg)
+/- weight
(kg)
+/- weight
(kg)
+/- weight (kg) +/-
2.0 2g 5.0 5g 10.0 10g 20.0 20g 50.0 50g 100.0 100g
4.0 2g 10.0 5g 20.0 10g 40.0 20g 100.0 50g 200.0 100g
6.0 4g 15.0 10g 30.0 20g 60.0 40g 150.0 100g 300.0 200g
6. Check other functions, such as TARE, MEMORY and Auto-Off.
4.2 Replacement of display PCBA
1. Disassemble the bottom housing of the remote display box.
2. Disconnect PL3, PL4 and PL5 from the display PCBA. Replace it by a new PCBA.
Connect PL3, PL4 and PL5 again.
3. Assemble the bottom housing.
4. Perform an internal adjusting as described in section 1.
5. Check the accuracy of the balance at different weights as described in the previous
section.
6. Check other functions, such as TARE, MEMORY and Auto-Off.
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5 Schematics
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6 Spare parts list
Part-No. Description
1 RDE-006-03-001 Overlay KERN DE6K2
2 RDE-015-03-001 Overlay KERN DE15K5
3 RDE-030-03-001 Overlay KERN DE30K10
4 RDE-060-03-001 Overlay KERN DE60K20
5 RDE-060-03-0L1 Overlay KERN DE60K20L
6 RDE-150-03-001 Overlay KERN DE150K50
7 RDE-150-03-0L1 Overlay KERN DE150K50L
8 RDE-300-03-001 Overlay KERN DE300K100
9 RDE-006-10-001 Display assy KERN DE 6K2
10 RDE-015-10-001 Display assy KERN DE 15K5
11 RDE-030-10-001 Display assy KERN DE 30K10
12 RDE-060-10-001 Display assy KERN DE60K20
13 RDE-150-10-001 Display assy KERN DE150K50
14 RDE-300-10-001 Display assy KERN DE300K100
15 RDE-060-10-002 Analog assy – for all models
16 440-902 Adaptor 230V~/50Hz/9V=
17 470-902-001 Adaptor 120V~/50Hz/9V=
18 470-902-002 Adaptor UK
19 470-902-003 Adaptor US 120V/60Hz/9V=
20 R440-000-13-001 Connection socket for adaptor
21 RDE-006-04-001 Weighing platform high-grade steel 310x310mm
22 DE-A02 Protection cover
23 DE-A01 Holder height 450mm
24 DE-A03 packing – without polystyrene
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