ESAB LTR 255 User manual

Brand: ESAB

Model: LTR 255

Category: Welding System

Type: User manual

0740 800 118

Valid for serial no. 745--xxx--xxxx to 011--xxx--xxxx040830

LTR 255

Power Tig 255

Service manual

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LIST OF CONTENTS Page

READ THIS FIRST 3................................................................

COMPONENT DESCRIPTION 4......................................................

WIRING DIAGRAM Valid for ser.no. 745--xxx--xxxx 8...................................

WIRING DIAGRAM Valid for ser.no. 842--xxx--xxxx and 011--xxx--xxxx 10...................

DESCRIPTION OF OPERATION, CIRCUIT BOARD AP01 12.............................

1 +30 V +20 V ±10 V Power supply 12............................................

2 Power supply to the fan 13.......................................................

3 Selection of welding method 13...................................................

4 Start / Stop, Reference input, Remote control input 14..............................

5 Slope up / Slope down 15........................................................

6 HF unit 15.....................................................................

7 Gas valve 16...................................................................

8a Shunt input 16..................................................................

8b Shunt input with shunt signal amplifier 17..........................................

9 Arc voltage sensing 18..........................................................

10 Gate circuit 19..................................................................

Checking the gate pulses 20.....................................................

11 Thermal overload switch 21......................................................

Component positions, circuit board AP01 0481 864 886 22.............................

Component positions, circuit board AP01 0481 818 890 23..............................

TRANSISTOR BOARD AP02 24......................................................

TRANSISTOR BOARD AP03 26......................................................

MOS TESTER 28....................................................................

SOFT STARTING 29.................................................................

SUPPRESSION BOARD AP08 30.....................................................

SUPPRESSION BOARD AP09 31.....................................................

DISASSEMBLY / REASSEMBLY 32....................................................

Assembling the diode modules 32....................................................

Removal of transistor circuit boards AP02 and AP03 33.................................

Refitting the transistor circuit board 33................................................

Fitting the main transformer TC02 34.................................................

TECHNICAL DATA 35................................................................

LOAD CHARACTERISTIC 36.........................................................

INSTRUCTIONS 37..................................................................

INTRODUCTION 37.................................................................

INSTALLATION 37..................................................................

OPERATION 38.....................................................................

MAINTENANCE 40..................................................................

SPARE PARTS 40...................................................................

NOTES 41..........................................................................

Rights reserved to alter specifications without notice.

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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 i n 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

August 2004.

The manual is valid for LTR 255 with serial numbers:

745--xxx--xxx, 842--xxx--xxxx, 011--xxx--xxxx.

The LTR 255 is designed and tested in accordance with international and European

standard IEC/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

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

S Install and earth the welding unit in accordance with applicable standards.

S Do not touch live electrical parts or electrodes with bare skin, wet gloves or wet clothing.

S Insulate yourself from earth and the workpiece.

S Ensure your working stance is safe.

FUMES AND GASES -- Can be dangerous to health

S Keep your head out of the fumes.

S Use 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.

S Protect your eyes and body. Use the correct welding screen and filter lens and wear protective

clothing.

S Protect bystanders with suitable screens or curtains.

FIRE HAZARD

S Sparks (spatter) can cause fire. Make sure therefore that there are no inflammable materials nearby.

NOISE -- Excessive noise can damage hearing

S Protect your ears. Use ear defenders or other hearing protection.

S Warn bystanders of the risk.

MALFUNCTION -- Call for expert assistance in the event of malfunction.

PROTECT YOURSELF AND OTHERS!

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COMPONENT DESCRIPTION

This component description refers to the wiring diagrams.

The LTR 255 is a primary--switched power unit, using parallel--connected MOSFET--transis -

tors as the switching elements. The switching frequency is 48.5 kHz. The conducting

interval varies between zero and 9.5 µs, depending on the welding current output. The

conducting time and frequency are controlled by circuit board AP01.

WARNING !

STATIC ELECTRICITY can damage circuit

boards and electronic components.

S Observe precautions for handling electrostatic

sensitive devices.

S Use proper static--proof bags and boxes.

ESD

AP01 The main circuit board with control electronics, see description on page 12.

AP02 Circuit board with power transistors for the positive pole,

see description on page 24.

WARNING! the transistors are connected to mains voltage potential.

AP03 Circuit board with power transistors for the negative pole,

see description on page 26.

WARNING! the transistors are connected to mains voltage potential.

AP08 Interference suppression circuit board. Prevents mains--borne interference.

Circuit diagram and component positions are on page 30.

AP09 Interference suppression circuit board, remote control connector, see the

diagram on page 31.

AP10 Circuit board with shunt signal amplifier. See the description on page 17.

Included in the LTR 255 from serial number 842--xxx--xxxx.

AP11 HF generator. See the description on page 15.

C01 Capacitor, transient protection.

C02, C03 Capacitor, 1000µF, buffer/smoothing capacitors. Time to discharge after

turning off the unit: about two minutes.

C04 -- C12 Decoupling capacitors.

Capacitor is not fitted from serial number 842--xxx--xxxx.

EV01 Fan, 24 VDC. Cooling the power unit.

EV02 Fan, 24 VDC. Cooling AP11 and TV01.

FU01 -- FU06 Fuses fitted to the control transformer. For fuse ratings: see item 212 in the

spare parts list.

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HL01 Lamp, 28 V, white, lights when mains power is on.

L01 Secondary inductor.

L03 -- L05 Ferrite ring core, transient protection.

L06 Ferrite tube, transient protection. The shunt cables are twisted and

wounded 3 tur ns through the ferrite tube. L06 is not mounted from serial

number 842--xxx--xxxx.

QF01 Mains power supply switch, 3--pole.

R01 Resistor , 3.9 kΩ 5W.

RP01 Potentiometer 500 kΩ. For gas post flow time 5 -- 20 seconds.

RP02 Potentiometer 500 kΩ. For slope down time 0.1 -- 10 seconds.

RP03 Potentiometer 10 kΩ. For welding current setting.

RS01 Shunt, 119 mV at 250 A. In machines with serial number 745--xxx--xxxx

the cables from the shunt are twisted. From serial number 842--xxx--xxxx a

shunt signal amplifier is fitted to the shunt.

SA01 Switch, 2/4--stroke changeover.

SA02 Selector switch: TIG Lift Arc / TIG HF / MMA

SA03 Switch, activation of remote control.

ST01 Thermal overload cutout, for overload protection, mounted in the welding

inductor (L01) winding. Breaks at 130 _C and resets at 100 _C.

TC01 Control power transformer. The primary is supplied at 400 V, with second-

ary output voltages of 26, 2x18, 19, 23 and 42 V.

From serial no. 011--207--xxxx the transformer is r eplaced by a new trans-

former with a stronger 26 V winding. Fuse FU2 is changed from 630 mA

to 800 mA. For other fuse ratings: see item 212 in the spare parts list.

TC02 Main transformer. For f itting instructions, see page 34.

TV01 HF transformer.

V01, V02 Mains rectifier bridges, 35 A, 1200 V. After replacing the rectifier bridges,

the machine must be soft--started: see instructions on page 29.

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V03,V04 Rectifier and freewheel diodes.

V03 rectifies the welding current. During the time interval between two

voltage pulses from transformer TC02, the freewheel diodes V04 maintain

the welding current from inductor L01.

On the cooling fins thr ee diode modules are mounted. Each diode module

consists of two diodes. If a freewheel diode (V04) is broken all modules

have to be replaced.

From serial number 011--148--xxxx a new diode module is used. The rated

current for the new module, SCOMES MKK300.4, is 300 A. The rated

current for the old module, Motorola MURP20040CT, is 200 A. Because of

the higher rating only two modules ar e needed for the rectifier unit. The

ordering no. for the new module is the same as for the old.

For installation instructions, see page 32.

V05 LED, yellow. Lights when thermal cutout ST01 operates (breaks) as a re-

sult of high temperature.

X01 -- X03 Terminal block.

XP01 Pin connector with jumper. Connected when the machine is used without

water cooler.

XS . . Sleeve connectors.

Note: the connectors XS01, XS02, XS03, XS05 and XS06 has changed

design. Valid from serial number 842--xxx--xxxx.

The sleeve numbering is reversed compared to the earlier version. The

wire numbering and the numbering of the contact pins of the circuit board

is not changed, compare the diagrams on page 8 and 10.

The ordering numbers for the connectors are listed under item 303 in the

spare parts list.

XS10 12--pole Burndy contact, for connection of remote control unit.

XS11 TIG central connector: only LTR 255 model --884.

XS12 2--pole Cannon connector, only LTR 255 model --885.

XS13 Welding current connector, OKC, only LTR 255 model --885.

XS14 Welding current terminals, (two), OKC type

XS24 Connection for 400V to water cooler. (The water cooler is an accessory,

which is mounted under the machine.)

XS25 Connection for water flow guard.

YV01 Solenoid valve

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WIRING DIAGRAM Valid for ser.no. 745--xxx--xxxx

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WIRING DIAGRAM Valid for ser.no. 842--xxx--xxxx and 011--xxx --xxxx

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DESCRIPTION OF OPERATION, CIRCUIT BOARD AP01

This description refers to the circuit diagrams on pages 8 and 10 and to the components

layout diagrams on pages 22 and 23.

Only those items that are connected to the inputs and outputs of the circuit board are

described here.

If there is a fault on the circuit board, the whole circuit board must be replaced.

After replacing the board, the machine must be soft--started, as described on page 29.

1 +30 V +20 V ±10 V Power supply

+30 V

Power supply to the gas and HF relays.

±10 V

Voltage tolerance ±5%. The power supply from transformer TC01 is protected by

two 1.25 A slow--blow fuses.

+20 V

Power supply to the control amplifier, the pulse width modulator and the gate

circuits.

Voltage tolerance ±5%. The power supply from transformer TC01 is protected by an

800 mA slow--blow fuse.

Capacitor C93 slows the rise time of the 20 V supply at power--on, which delays the

gate pulses to the MOSFET transistors.

HL01 is an indicating lamp on the front of the machine, lighting to indicate that the

main power switch is On.

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2 Power supply to the fan

The LTR 255 is fitted with two DC--powered fans. They are supplied at 28 V ±5%

from voltage regulator VR5. The power supply from transformer TC01 is protected

by a 630 mA slow--blow fuse.

Fan EV01 is cooling the power unit (AP02, AP03, V01, V02, V03 and V04).

Fan EV02 is cooling the HF unit AP11 and transformer TV01.

3 Selection of welding method

MMA, LiftArc, HF

Switch SA02 selects the welding method by disabling, through a diode network, the

functions that ar e not

to be active for a particular welding method.

2--stroke/4--stroke

Closing switch SA01 selects 2--stroke control mode.

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4 Start / Stop, Reference input, Remote control input

Reference input/Remote control input

This input has its own power supply and a high--impedance input to the control

amplifier. This protects it against short circuits between the remote control cable

and the welding circuit.

Voltage regulator VR1 incorporates internal thermal protection against overload.

At the lowest current reference, the voltage at circuit board contact C9 is 0 V. At the

maximum current reference, the voltage is about 14 -- 15 V.

Resistor R74 adjusts the output voltage from VR1 so that the reference voltage and

the control amplifier provide the correct maximum current. This resistor is adjusted

during manufacture of the circuit board, and should not subsequently be adjusted.

Switch SA03 selects adjustment of the welding current from the remote control

device or from the front panel of the machine.

If it is the Remote position, but no remote control device is connected, resistor R75

holds the current reference at the minimum level.

Start/Stop

When operating in TIG welding mode, the machine is started from the welding torch

switch, which is connected to the machine via contacts XS11/XS12. Alternatively,

welding can be started from a remote control device and connectors J and K in

remote control unit contact XS10. Relay RE1 is used only during TIG starts. See

also the description of arc voltage sensing on page 18.

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5 Slope up / Slope down

Potentiometer RP02 on the front of the machine is used for setting the Slope Down

time (the decay time f or the welding current when TIG--welding). The time is

adjustable between 0.1 and 10 seconds.

Potentiometer R58 on the circuit board controls the Slope Up time (the rise time for

the welding curr ent when TIG--welding). It is adjustable between 0 and 5 seconds.

On delivery, the Slope Up time has been set at 0.

6 HF unit

WARNING! dangerous voltage.

When the torch switch is closed and the open--circuit voltage exceeds about 45 V,

relay RE3 closes and activates HF unit AP11. The relay drops off when the arc

voltage is less than 45 V or if the arc has not struck within 0.5 seconds.

In the MMA welding mode, transistor Q7 is held off by --10 V from diode D18. In

the Lift Arc mode, Q7 is held off by --10 V from diode D17.

The voltage on the primary side of HF transformer TV01 is about 400 V, and the

secondary voltage is about 8 kV.

From serial number xxx--006--xxxx a new type of HF generator is used,

0367 268 001. This generator produces about 500 V on the primary side of the HF

transformer and about 10 kV on the secondary side.

The new HF generator replaces the old type as spare part for older machines. The

colour of the new type is grey, the old is black. The new has screw connections for

the connection cables and different hole pattern for the mounting.

When fitting the new generator to older machines: three new mounting holes for the

generator must be drilled and the cable shoes must be removed from the connection

cables. Fit the generator with the connection ter minal turned towards the base plate.

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7 Gas valve

Gas valve YV1 is controlled by relay RE2. Potentiometer RP01, on the front panel

of the machine, is used for adjusting the gas post--flow time in the range 5--20

seconds.

Potentiometer R30, on the circuit board, controls the gas pre--flow time between 0

and 5 seconds. When delivered, it is set at 0 seconds.

The gas valve is activated briefly when the machine is energised.

8a Shunt input

Shunt input for LTR 255 with serial number 745--xxx--xxxx.

The shunt provides a signal of 119 mV at a welding current of 250 A.

The wires (B1 and B2) between the shunt and the circuit board must be twisted in

order to prevent any interference reaching the circuit board.

The shunt wires are wounded 3 turns through a ferrite tube L06, see the wiring

diagram on page 8.

Do not mix up the wires. If you mix up B1 and B2, you will get a current surge that

will destroy the machine.

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8b Shunt input with shunt signal amplifier

Shunt input for the LTR 255 from serial number 842--xxx--xxxx

The shunt signal amplifier board AP10 is voltage supplied from circuit board AP01.

Resistor R16 adjusts the offset voltage of amplifier IC1. This resistor is adjusted

during manufacture of the circuit board, and should not subsequently be adjusted.

The signal amplification is set by fixed resistors and it is not adjustable.

The shunt voltage is 119 mV at 250 A welding current. The voltage between the

contacts B1 and B2 on circuit board AP01 must be 5.0 V ±2% at 250 A welding

current.

Component positions, circuit board AP10

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9 Arc voltage sensin g

Machines with shunt signal amplifier: The arc voltage from RS01 is connected to

AP01 through AP10. The resistors R172 and R177, with the value 0 Ω,are

mounted. The capacitors C52 and C95 are not mounted on the board.

Machines without shunt signal amplifier: The arc voltage from RS01 is

connected directly to AP01. The resistors R172 and R177 are not mounted. The

capacitors C52 and C95 are mounted on the board.

The arc voltage signal limits the open--circuit voltage and is also used to sense the

start of welding. During TIG welding, the arc voltage can vary between 5 and 45 V.

The following description describes the starting sequence for the various welding

modes:

MMA

1. Open--circuit voltage control. Open--circuit voltage is 70--90 V.

2. A voltage less than 45 V is interpreted as a welding start. The control amplifier

generates an elevated starting current for about 300 ms.

The starting current is 75% higher than the set value of curr ent when the set

value is 25 A. The starting current is 25% higher than the set value of current

when the set value is 160 A.

3. Welding is performed at the set value of current.

TIG, HF STAR T

1. Gas pre--flow.

2. The starting voltage is about 100 V, and HF ignition is provided for a maximum

of 0.5 seconds.

3. A voltage less than 45 V is interpreted as a welding start. The control amplifier

generates an elevated starting current for about 50 ms.

The starting current is 20 A higher than the set value of current.

4. Welding is performed at the set value of current.

TIG, LIFTARC START

1. Gas pre--flow.

2. Open--circuit voltage is 70--90 V. Contact with the workpiece causes the control

amplifier to generate a sensing current, which is limited to 8 A.

3. When the electrode is lifted from the workpiece and the arc voltage exceeds

5 V, the control amplifier generates an elevated starting current for about 50 ms.

The starting current is 20 A higher than the set value of current.

4. Welding is performed at the set value of current.

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10 Gate circuit

The pulse width modulator IC13 deter mines the frequency and pulse time of the

MOSFET transistors’ control pulses.

It is important that the frequency and maximum pulse time are within the specified

tolerances. The pulse frequency is 48.5 ¦0.5 kHz and t he maximum pulse time is

43 ¦1% of the cycle time.

Maximum pulse time results in maximum current and voltage.

IMPORTANT

The frequency and pulse time are very important parameters. If they are

incorrect, they can result in transistor failure in the main circuit.

See also CHECKING THE GATE PULSES on next page.

The MOSFET transistors’ drive stage produces control pulses for the gate--source on

the power transistors. There is a separate output for each switch unit.

All gate circuits are galvanically isolated from other circuits on the board. The

insulation voltage between the pulse width modulator and the gate circuits is 4 kV.

WARNING! The gate circuits are at mains voltage.

The two gate circuits are identical, and so only one is described here.

When Q17 conducts, a voltage pulse is produced on the transformer’s secondary

winding. This pulse is conducted via D40, D43 and output J1 to the gate on the

MOSFET transistors. The pulse returns via the source, connection J2, D42 and C79.

The mean peak gate -- source voltage is 12 -- 15 V.

The gate pulse between J1 and J2 charges C79 to 5.6 V. When Q17 turns off, the

voltage from the secondary of the pulse transformer changes polarity, causing Q18

and Q19 to start to conduct. The gate voltage becomes negative, turning off the

MOSFET transistors.

When checking the gate pulses, connect a dummy gate load to the circuit board, see

instructions on next page.

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Checking th e gate pulses

If circuit board AP02 or AP03 has failed, the gate pulses must always be checked.

Remove connections XS07 and XS08 (gate pulses). Connect a dummy gate load to

outputs J1 and J2 and to K1 and K2.

Dummy gate load

A set of different gate loads can be ordered from ESAB.

The part number is 0468 469 003. The gate loads can be used to the following

machines: LUC, LHL 130/160, LHL 250/315, LTL 160, LTL315, LUB 315,

LHN, LTN, LTR, LTO, MechTig 315 and Protig 315.

IMPORTANT: never

check the gate pulses when AP02 and AP03 are

connected to AP01: use a dummy gate load.

AP02 and AP03 are at mains volt age potential.

The minimum gate pulse level must be --3.5 to --5.5 V and its maximum value must

be 12 to 15 V. The frequency must be 48. 5 kHz ¦0.5 kHz. Check that the

maximum pulse time is 43 ¦1% of the cycle time, measured at a level of +5 V.

If the gate pulse does not lie within these tolerances, replace circuit board AP01.

After replacing AP01, check the gate pulses again and soft--start the machine, as

described on page 29.

Gate pulses as measured across a dummy gate load on circuit board AP01

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ESAB LTR 255 User manual

Brand: ESAB

Model: LTR 255

Category: Welding System

Type: User manual

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ESAB LTR 255 User manual

ESAB LTR 255 User manual

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