ESAB MEK 4 User manual

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0740 800 085 Valid for serial no. 431--xxx--xxxx to 826--xxx--xxxx040426
MEK 4
Service manual

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LIST OF CONTENTS Page
READ THIS FIRST 2.......................................
COMPONENT DESCRIPTION 4.............................
WIRING DIAGRAM
Valid for serial no. 431--xxx--xxxx 5..........................
WIRING DIAGRAM
Valid for serial no. 514--xxx--xxxx to 826--xxx--xxxx 6............
DESCRIPTION OF OPERATION 7...........................
Design changes 7...........................................
1 Power supply 9.........................................
2 Activation, contactor 9...................................
3 Crater filling 10...........................................
4 Voltage adjustment 12....................................
5 Gas valve 14............................................
6 2--stroke / 4--stroke 15....................................
7 Burn--back time 15.......................................
8 Wire feed speed 16.......................................
9 Creep start / Normal start 17...............................
10 Motor driving / braking 18..................................
11 Tachometer input 19......................................
12 Current relay 19..........................................
13 Start / Stop 20...........................................
14 Processor 20............................................
15 Remote control input 21...................................
16 Digital display 22.........................................
TECHNICAL DATA 24.......................................
MAINTENANCE 24.........................................
SETTING THE WIRE FEED PRESSURE 25...................
CONTROL PANEL AND CONNECTIONS 26...................
ACCESSORIES 27.........................................
SPARE PARTS 28..........................................
NOTES 28.................................................
READ THIS FIRST
Maintenance and repair work should be performed by an experienced person, and electrical
work only by a trained electrician. Use only recommended replacement parts.
This service manual is intended for use by technicians with electrical/electronic training for
help in connection with fault--tracing and repair.
Use the wiring diagram as a form of index for the description of operation. The circuit
board is divided into numbered blocks, which are described individually in more detail in
the description of operation. All component names in the wiring diagram are listed in the
component description.
This manual contains details of all design changes that have been made up to and including
February 2003.
Rights reserved to alter specifications without notice.

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The MEK 4 wire feed unit is designed and tested in accordance with European
standard EN 60974--1 and EN 50199.
On completion of service or repair work, it is the responsibility of the person(s) etc.
performing the work to ensure that the product does not depart from the requirements
of the above standard.
WARNING !
STATIC ELECTRICITY can damage circuit
boards and electronic components.
SObserve precautions for handling electrostatic
sensitive devices.
SUse proper static--proof bags and boxes.
ESD
WARNING
READ AND UNDERSTAND THE INSTRUCTION MANUAL BEFORE INSTALLING OR OPERATING.
ARC WELDING AND CUTTING CAN BE INJURIOUS TO YOURSELF AND OTHERS. TAKE PRECAU-
TIONS WHEN WELDING. ASK FOR YOUR EMPLOYER’S SAFETY PRACTICES WHICH SHOULD BE
BASED ON MANUFACTURERS’ HAZARD DATA.
ELECTRIC SHOCK -- Can kill
SInstall and earth the welding unit in accordance with applicable standards.
SDo not touch live electrical parts or electrodes with bare skin, wet gloves or wet clothing.
SInsulate yourself from earth and the workpiece.
SEnsure your working stance is safe.
FUMES AND GASES -- Can be dangerous to health
SKeep your head out of the fumes.
SUse ventilation, extraction at the arc, or both, to keep fumes and gases from your breathing zone and
the general area.
ARC RAYS -- Can injure eyes and burn skin.
SProtect your eyes and body. Use the correct welding screen and filter lens and wear protective
clothing.
SProtect bystanders with suitable screens or curtains.
FIRE HAZARD
SSparks (spatter) can cause fire. Make sure therefore that there are no inflammable materials nearby.
NOISE -- Excessive noise can damage hearing
SProtect your ears. Use ear defenders or other hearing protection.
SWarn bystanders of the risk.
MALFUNCTION -- Call for expert assistance in the event of malfunction.
PROTECT YOURSELF AND OTHERS!
WARNING!
Rotating parts can cause injury, take great care

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COMPONENT DESCRIPTION
This component description refers to the wiring diagram.
AP01 Main circuit board with control electronics: see the description on
page 7.
AP02 Circuit board with display: see the description on page 22.
C01 Capacitor 0.1µF, decoupling.
CXX Capacitor 4700µF. Must be fitted when an intermediate wire feed unit is
in use in extreme applications (low mains voltage and long cables).
G01 Tachogenerator: 660 Hz output at a wire speed of 25 m/min. The
tachogenerator is incorporated in motor M01.
M01 Motor, rated voltage 42 V.
RP01 Potentiometer, 10 kΩ, for setting the wire feed speed.
RP02 Potentiometer, 10 kΩ, for setting the welding voltage.
RP03 Potentiometer, 10 kΩ, for setting the burn--back time.
RP04 Potentiometer, 10 kΩ, for setting the crater fill time.
SA01 Switch, 2/4--stroke changeover. When the switch is closed, 4--stroke
control mode is selected.
SA02 Switch, Crater fill function On/Off. When the switch is closed, crater fill
function is operative.
XP01 23--pole connector, for connection to the welding power unit.
XP02 Terminal for welding current connection from the power unit.
XS . . Connectors marked XS are socket connectors.
XS02 If circuit board AP01 has part no. 0486 205 880 or 0486 205 882:
the Creep Start function is operative when the connector links B01--B02.
If circuit board AP01 has part no. 0486 205 886 or 0487 166 880:
the Creep Start function is operative when the connector links B02--B03.
XS12 Not mounted, from machine number 514--615--xxxx
XS13 12--pole connector:
MEK 4 with serial number 431--xxx--xxxx
23--pole connector:
MEK 4 from serial number 514--xxx--xxxx and above.
YV01 Solenoid valve

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WIRING DIAGRAM Valid for serial no. 431--xxx--xxxx
MEK 4
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See page 17

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WIRING DIAGRAM Valid for serial no. 514--xxx--xxxx to 826--xxx--xxxx
MEK 4
See page 17

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DESCRIPTION OF OPERATION
Design changes
The following changes have been introduced, with effect from serial no. 514 . . . . . .
1. Remote control socket outlet XS13 has been changed from a 12--pole socket to a 23--pole
socket.
2. Power supply arrangements to the remote control unit have been changed. See items 4a,
4b and 8a, 8b in the Function Description. See also item 15b.
3. The power supply connections for the solenoid valve in the intermediate wire feed unit
have been changed from J and K to U and V. See items 5b and 15b in the Function
Description.
4. A new circuit board (486 205--882) replaces circuit board 486 205--880. It can be used
as a replacement part in all MEK 4 units. The following changes have been introduced
on the new board:
a. New program version, with modified creep start characteristics.
See items 9 and 14 in the Function Description.
b. Higher current limit for the motor, which improves acceleration and starting.
See item 10 in the Function Description.
c. The 0 VB voltage from the power unit is no longer galvanically isolated from 0 V in
the wire feed unit, in order to allow other remote control devices to be used. The
two neutrals are connected via diode D35.
See items 4a, 4b and 8a, 8b in the Function Description. See also the component
positions diagram.
5. The circuit board is now contained in a larger screened enclosure, item 227 in the Spare
Parts List. The guard for the screened enclosure and the wiring harness, item 228 in the
Spare Parts List, is also larger. However, when fitting the new circuit board in older
MEK 4 machines, it is not necessary to replace the screened enclosure or guard.
6. Actual voltage is now measured. This involves a new conductor, no. 613 in the wiring
diagram. It runs from the motor body (the welding wire) to connector XP01;H. This
connectionworksonlywithLAWpowerunitswithserialnumbers 512 ... .... and
above, or with modified LAW power units. Note that modifying LAW power units in-
volves fitting the new circuit board (486 291--880) and modifying the wiring in the
power unit.
7. A cooling water connection has been introduced as an accessory: see item 7 in the
Accessories List.
An adapter for a 5 kg bobbin is now available as an accessory: see item 8 in the
Accessories List.
8. The above changes have resulted in corresponding changes to the following points of the
Spare Parts List: 214, 215, 225, 226, 227 and 228.
The following change has been introduced, with effect from serial no. 514 615 ....
1. The cables 401, 402 and connector XS12 are not mounted in the machine. See item 11
in the Description of operation.

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** Circuit board 0486 205 880 is supplied with capacitor C35, on circuit board 0486 205 882
capacitor C35 is replaced by diode D35. See the description of operation, items 4a and 4b.
Component positions, circuit board AP01
**

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Sections 1--16 below refer to the /wiring diagrams on pages 5 and 6.
The circuit board is screened by a metal casing, connected to 0 V in the wire feed unit.
1 Power supply
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The wire feed unit receives 42 V from the control power supply transformer in the
welding power unit via connector XP01. LAW 400 and 500 welding power units
can supply a maximum of 6 A to the MEK 4. The wire feed unit’s own power
requirement at maximum load is 5 A.
42 V AC is supplied to the welding gun trigger switch, the gas valve and the
contactor. In addition, terminals G01 and G02 supply 42 V to a Miggytrac unit if
this is used together with the MEK 4.
DC power supplies
Diodes D30 -- D33 rectify the 42 V supply to 60 V. Capacitor C61 smooths the
supply, which is then used to power the wire feeder motor.
Transistor Q2 is a pre--regulator that drops the voltage from 60 V to 20 V. Q2 is
current--limited to about 200 mA.
VR1 and VR2 are voltage regulators, producing 5 V and 15 V respectively. The
circuit board’s microprocessor monitors the voltages. If the 15 V supply falls below
13 V, the wire feed unit is stopped.
2 Activation, contactor
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The welding power unit contactor is connected to the wire feed unit via pin F in
connector XP01. In the LAW 400/500 power units triac TC1 is loaded by a 1 kΩ
resistor.

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3 Crater filling
The crater fill function can be used when the MEK 4 is working
with a LAW power unit.
The crater fill function comprises the following modules :
SAn input for selecting crater fill function On/Off.
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Closing switch SA02 activates the function.
SPotentiometer RP04 sets the crater fill time.
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Times between 0 and 5.1 seconds can be set.
SAn output, XP01;W, which supplies a signal to the power unit when the voltage
is to be reduced for crater filling.
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The emitter of the transistor in optocoupler IC10 is connected to 0 VB, i.e. to
the neutral of the power unit voltage reference.
The crater fill function operates as follows :
Phase 1
When in 2--stroke control mode, releasing the welding gun trigger switch reduces the
wire feed speed to 84% of its original value. In 4--stroke control mode, crater filling
starts when the trigger switch is pressed for the second time. Optocoupler IC10 is
activated, supplying a signal to the power unit that crater filling has started, causing
the power unit to reduce its output voltage.
Phase 1 continues for a time as determined by the setting of potentiometer RP04, up
to a maximum of 1.27 seconds.

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Phase 2
Phase 2 starts when phase 1 finishes. The wire feed unit further reduces the wire
speed to 84% of the value during phase 1. Optocoupler IC10 turns off, giving the
power unit a signal further to reduce the voltage. Phase 2 continues also for a
maximum of 1.27 seconds.
Phases 3 and 4
Phases 3 and 4 are repeats of phases 1 and 2. After phase 4, during which wire feed
speed is 50 % of the original value, welding concludes with the preset burn--back
time.
If, when in 4--stroke control mode, the welding gun trigger switch is released while
crater filling is in progress, crater filling will be interrupted.
Wire feed speed and welding voltage during crater filling

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4a Voltage adjustment
Applies to MEK 4 with serial number 431 . . . . . .
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Voltage adjustment, circuit board AP01 with article number 0486 205 880
When the MEK 4 is connected to a power unit with steplessly variable output
voltage, potentiometer RP02 on the front of the unit can be used to control the power
unit output voltage.
The +15 VB and 0 VB voltages are supplied by the power unit via connector XP01.
The voltage adjustment circuits are galvanically isolated from the other circuits at
circuit board AP01.
The remote control unit for voltage control is connected to pins F, G, H, L and M in
connector XS13. A link must be fitted between pins L and M in order to activate the
unit.
Voltage adjustment, circuit board AP01 with article number 0486 205 882
The voltage adjustment circuits are not galvanically isolated from the other circuits
on the board when circuit board --882 is used.

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4b Voltage adjustment
Applies to MEK 4 with serial number 514 . . . . . . and above.
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Voltage adjustment, circuit board AP01 with article number 0486 205 882
When the MEK 4 is connected to a power unit with steplessly variable output
voltage, potentiometer RP02 on the front of the unit can be used to control the power
unit output voltage.
The +15 VB and 0 VB voltages are supplied by the power unit via connector XP01.
The voltage adjustment circuits are not galvanically isolated from the other circuits
at circuit board AP01.
The remote control unit for voltage control is connected to pins J, K, L, Z and Y in
connector XS13. A link must be fitted between pins Z and Y in order to activate the
unit.

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5a Gas valve
Applies to MEK 4 with serial number 431 . . . . . .
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The gas valve is connected to connectors F04 and F05. If an intermediate wire feed
unit is being used, its gas valve is connected via pins K and J in the remote control
connector (XS13).
5b Gas valve
Applies to MEK 4 with serial number 514 . . . . . . and above.
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The gas valve is connected to connectors F04 and F05. If an intermediate wire feed
unit is being used, its gas valve is connected via pins V and U in the remote control
connector (XS13).

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6 2--stroke / 4--stroke
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2--stroke
When switch SA01 is open, 2--stroke control mode is selected. This means that
closing the welding gun trigger switch starts the wire feed motor, opens the gas valve
and closes the power unit contactor.
Releasing the switch stops the motor, releases the contactor and closes the gas valve.
If crater filling and/or burn--back time are operative, they will be activated before
welding ceases.
4--stroke
When switch SA01 is closed, 4--stroke control mode is selected. This means that
first closure of the trigger switch operates the gas valve, with the wire feed motor
starting, and the power unit contactor operating, when the trigger switch is released.
Closing the trigger switch for the second time stops the motor and de--energises the
contactor in the power unit. Releasing the switch closes the gas valve.
If crater filling and/or burn--back time are operative, they will be activated before
welding ceases.
7 Burn--back time
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The burn--back time is the time from when motor braking starts until the machine
contactor opens. It can be adjusted by potentiometer RP03 between 0 and 0.5
seconds.

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8a Wire feed speed
Applies to MEK 4 with serial number 431 . . . . . .
ADJUSTMENT ON THE FRONT PANEL OF THE FEEDER UNIT
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Potentiometer RP01 controls the wire feed speed over a range from 1.9 to 25
metres/minute. For use with automated welding processes, a 0 -- 10 V reference
signal can be connected to terminal A17.
ADJUSTMENT USING THE REMOTE CONTROL UNIT
Wire feed speed reference from the remote control unit
Potentiometer RP01 is disengaged when a remote control unit is connected to input
XS13. The circuit board microprocessor senses that the remote control unit is
connected by means of the voltage drop across diode D1. When the remote control
unit is connected, the voltage on connector E11 cannot drop below about 0.6 V.
8b Wire feed speed
Applies to MEK 4 with serial number 514 . . . . . . and above.
ADJUSTMENT ON THE FRONT PANEL OF THE FEEDER UNIT
The function is the same as described in item 8a above.
ADJUSTMENT USING THE REMOTE CONTROL UNIT
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Wire feed speed reference from the remote control unit

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Potentiometer RP01 is disengaged when a remote control unit is connected to input
XS13. The circuit board microprocessor senses that the remote control unit is
connected by means of the voltage drop across diode D35. When the remote control
unit is connected, the voltage on connector E11 cannot drop below about 0.6 V.
9 Creep start / Normal start
Creep start means that the motor runs at a speed of 1.9 m/minute until the current
relay is activated. When the relay operates, the speed increases to the set speed.
If the current relay has not operated within one second after starting, the motor
increases to the set speed.
MEK 4 with circuit board 0486 205 880 will start at a speed of 3 m/minute when the
creep start is activated. If the set speed is less than 3 m/minute, wire feed starts at
the set speed.
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Activation of creep start, circuit boards with part no. 0486 205 880 and 0486 205 882
The wire feed unit is delivered with creep start activated. If it is to be disengaged, so
that the unit starts immediately at the set speed, connector XS02 must be changed
over.
Note: creep start is activated when terminals B01 and B02 are short--circuited by
connector XS02.
Spare part boards
Circuit boards with part no. 0486 205 886 and 0487 166 880 can be used as spare
parts to the MEK 4.
Note: if these boards are used, creep start is activated when terminals B02 and B03
are short--circuited by connector XS02.
Activation of creep start, circuit boards with part no. 0486 205 886 and 0487 166 880

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10 Motor driving / braking
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The motor is powered by the smoothed +60 V supply. Pulse width modulation,
controlled by transistor Q3, is used to vary the motor voltage. The pulse frequency
is 12 kHz, and the maximum conducting time of the pulses is 97% of the pulse cycle
time. Freewheel diode D11 maintains motor current during the pulse breaks.
At a supply voltage of 42 V, the wire feed drive roller has a speed of 258 r/min. At a
drive roller speed of 266 r/min, the wire feed speed is 25 m/min.
Pins D and E in the remote control unit connector XS13 provide power for the motor
in an intermediate wire feed unit or for a PKE (push/pull) welding gun. If an
intermediate wire feed unit is being used in extreme applications (low mains voltage
and long cables), an additional 4700µF smoothing capacitor CXX must be connected
(ordering number 0193 141 048).
The voltage drop across resistor R92 provides a signal that is proportional to the
motor current. When the current exceeds 15.4 A, IC6:2 turns off the gate pulse to
Q3. When the current drops, Q3 conducts again at the next gate pulse.
Circuit board AP01 with article number 0486 205 880 was delivered with a current
limit of 7A. The current limit of this circuit boards can be changed by replacing
R41. R41 = 220 Ω⇒7 A current limit. R41 = 470 Ω⇒15.4 A current limit.
Circuit board AP01 with article number 0486 205 882 is delivered with a current
limit of 15.4A.

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BRAKING
When the motor starts, capacitor C60 charges up to 15 V, with zener diode D20
limiting the voltage across it. Braking is activated by the optocoupler IC3. When
the transistor in IC3 is turned on by the LED, 15 V from capacitor C60 is connected
to the gate of transistor Q4. Transistor Q4 turns on and short circuits the motor
through the resistors R85 and R86. The resistors limit the braking current to about
20 A.
11 Tachometer input
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XS12
XS12
The tachometer G01 is fitted inside the motor casing. At a wire feed speed of 25
m/min, it produces a signal frequency of 660 Hz.
Comparator IC5;2 converts the sine wave signal from the tachogenerator to a square
wave at the same frequency.
Pins XP01;R and XP01;S are used if there is a separate display unit for showing wire
feed speed. The digital displays in the MEK 4 and the LAW power units cannot
show the wire feed speed. Connections D01 -- D02 are used only if there is an
external instrument for displaying the wire feed speed.
Wires 401, 402 and connector XS12 are not fitted from serial number 514 615 ....
and above.
12 Current relay
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The current relay operates if the welding current exceeds 20 A. If the creep start
function has been selected, this is disengaged when the current relay operates. If the
crater filling function has been selected, it will work only when the current relay has
operated.

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13 Start / Stop
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The trigger switch in the welding gun is supplied at 42 V AC. Closing the switch
energises optocoupler IC10, pulling down the voltage across C46.
14 Processor
The processor stores the machine program. It monitors the power supply voltages:
if the voltages drop to too low a level, wire feed is stopped, as described in section 1
above.
The processor also monitors speed. If the wire speed deviates from the set value by
more than 1.5 m/min for more than five seconds, wire feed will be stopped.
Frommachineserialnumber 514 ... .... theprogramversionoftheprocessoris
changed to P1.02 (the previous version was P1.00, circuit board AP01 with part
number 0486 205 880). The change in the program affects the creep start: see
Creep start / Normal start on page 17.