cover1 5/92* − ST-157 072-A PRINTED IN USA
IMPORTANT: Read and understand the entire contents of this manual, with special emphasis on the safety
material throughout the manual, before installing, operating, or maintaining this equipment. This unit and these
instructions are for use only by persons trained and experienced in the safe operation of welding equipment. Do
not allow untrained persons to install, operate, or maintain this unit. Contact your distributor if you do not fully
understand these instructions.
OWNER’S MANUAL
®
December 1997 Form: OM-154 501G
Effective With Serial No. KH511668
MW250
ARC WELDING SAFETY PRECAUTIONS
WARNING
PROTECT YOURSELF AND OTHERS FROM POSSIBLE SERIOUS INJURY OR DEATH. KEEP CHILDREN
AWAY. PACEMAKER WEARERS KEEP AWAY UNTIL CONSULTING YOUR DOCTOR.
In welding, as in most jobs, exposure to certain hazards occurs. Welding is safe when precautions are taken. The
safety information given below is only a summary of the more complete safety information that will be found in the
Safety Standards listed on the next page. Read and follow all Safety Standards.
HAVE ALL INSTALLATION, OPERATION, MAINTENANCE, AND REPAIR WORK PERFORMED ONLY BY
QUALIFIED PEOPLE.
ARC WELDING can be hazardous.
ELECTRIC SHOCK can kill.
Touching live electrical parts can cause fatal shocks
or severe burns. The electrode and work circuit is
electrically live whenever the output is on. The input
power circuit and machine internal circuits are also
live when power is on. In semiautomatic or automatic
wire welding, the wire, wire reel, drive roll housing, and
all metal parts touching the welding wire are
electrically live. Incorrectly installed or improperly
grounded equipment is a hazard.
1. Do not touch live electrical parts.
2. Wear dry, hole-free insulating gloves and body protection.
3. Insulate yourself from work and ground using dry insulating mats
or covers.
4. Disconnect input power or stop engine before installing or
servicing this equipment.
5. Properly install and ground this equipment according to its
Owner’s Manual and national, state, and local codes.
6. Turn off all equipment when not in use.
7. Do not use worn, damaged, undersized, or poorly spliced cables.
8. Do not wrap cables around your body.
9. Ground the workpiece to a good electrical (earth) ground.
10. Do not touch electrode while in contact with the work (ground)
circuit.
11. Use only well-maintained equipment. Repair or replace
damaged parts at once.
12. Wear a safety harness to prevent falling if working above floor
level.
13. Keep all panels and covers securely in place.
ARC RAYS can burn eyes and skin;
NOISE can damage hearing.
Arc rays from the welding process produce intense
heat and strong ultraviolet rays that can burn eyes and
skin. Noise from some processes can damage
hearing.
1. Wear a welding helmet fitted with a proper shade of filter (see
ANSI Z49.1 listed in Safety Standards) to protect your face and
eyes when welding or watching.
2. Wear approved safety glasses. Side shields recommended.
3. Use protective screens or barriers to protect others from flash
and glare; warn others not to watch the arc.
4. Wear protective clothing made from durable, flame-resistant
material (wool and leather) and foot protection.
5. Use approved ear plugs or ear muffs if noise level is high.
FUMES AND GASES can be hazardous
to your health.
Welding produces fumes and gases. Breathing these
fumes and gases can be hazardous to your health.
1. Keep your head out of the fumes. Do not breathe the fumes.
2. If inside, ventilate the area and/or use exhaust at the arc to
remove welding fumes and gases.
3. If ventilation is poor, use an approved air-supplied respirator.
4. Read the Material Safety Data Sheets (MSDSs) and the
manufacturer’s instruction for metals, consumables, coatings,
and cleaners.
5. Work in a confined space only if it is well ventilated, or while
wearing an air-supplied respirator. Shielding gases used for
welding can displace air causing injury or death. Be sure the
breathing air is safe.
6. Do not weld in locations near degreasing, cleaning, or spraying
operations. The heat and rays of the arc can react with vapors to
form highly toxic and irritating gases.
7. Do not weld on coated metals, such as galvanized, lead, or
cadmium plated steel, unless the coating is removed from the
weld area, the area is well ventilated, and if necessary, while
wearing an air-supplied respirator. The coatings and any metals
containing these elements can give off toxic fumes if welded.
WELDING can cause fire or explosion.
Sparks and spatter fly off from the welding arc. The
flying sparks and hot metal, weld spatter, hot
workpiece, and hot equipment can cause fires and
burns. Accidental contact of electrode or welding wire
to metal objects can cause sparks, overheating, or
fire.
1. Protect yourself and others from flying sparks and hot metal.
2. Do not weld where flying sparks can strike flammable material.
3. Remove all flammables within 35 ft (10.7 m) of the welding arc. If
this is not possible, tightly cover them with approved covers.
4. Be alert that welding sparks and hot materials from welding can
easily go through small cracks and openings to adjacent areas.
5. Watch for fire, and keep a fire extinguisher nearby.
6. Be aware that welding on a ceiling, floor, bulkhead, or partition
can cause fire on the hidden side.
7. Do not weld on closed containers such as tanks or drums.
8. Connect work cable to the work as close to the welding area as
practical to prevent welding current from traveling long, possibly
unknown paths and causing electric shock and fire hazards.
9. Do not use welder to thaw frozen pipes.
10. Remove stick electrode from holder or cut off welding wire at
contact tip when not in use.
11. Wear oil-free protective garments such as leather gloves, heavy
shirt, cuffless trousers, high shoes, and a cap.
FLYING SPARKS AND HOT METAL can
cause injury.
Chipping and grinding cause flying metal. As welds
cool, they can throw off slag.
1. Wear approved face shield or safety goggles. Side shields
recommended.
2. Wear proper body protection to protect skin.
CYLINDERS can explode if damaged.
Shielding gas cylinders contain gas under high
pressure. If damaged, a cylinder can explode. Since
gas cylinders are normally part of the welding
process, be sure to treat them carefully.
1. Protect compressed gas cylinders from excessive heat,
mechanical shocks, and arcs.
2. Install and secure cylinders in an upright position by chaining
them to a stationary support or equipment cylinder rack to
prevent falling or tipping.
3. Keep cylinders away from any welding or other electrical circuits.
4. Never allow a welding electrode to touch any cylinder.
5. Use only correct shielding gas cylinders, regulators, hoses, and
fittings designed for the specific application; maintain them and
associated parts in good condition.
6. Turn face away from valve outlet when opening cylinder valve.
7. Keep protective cap in place over valve except when cylinder is
in use or connected for use.
8. Read and follow instructions on compressed gas cylinders,
associated equipment, and CGA publication P-1 listed in Safety
Standards.
PRINCIPAL SAFETY STANDARDS
Safety in Welding and Cutting, ANSI Standard Z49.1, from American Welding Society, 550 N.W. LeJeune Rd, Miami FL 33126
Safety and Health Standards, OSHA 29 CFR 1910, from Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.
Recommended Safe Practices for the Preparation for Welding and Cutting of Containers That Have Held Hazardous Substances, American Welding
Society Standard AWS F4.1, from American Welding Society, 550 N.W. LeJeune Rd, Miami, FL 33126
National Electrical Code, NFPA Standard 70, from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269.
Safe Handling of Compressed Gases in Cylinders, CGA Pamphlet P-1, from Compressed Gas Association, 1235 Jefferson Davis Highway, Suite 501,
Arlington, VA 22202.
Code for Safety in Welding and Cutting, CSA Standard W117.2, from Canadian Standards Association, Standards Sales, 178 Rexdale Boulevard,
Rexdale, Ontario, Canada M9W 1R3.
Safe Practices For Occupation And Educational Eye And Face Protection, ANSI Standard Z87.1, from American National Standards Institute, 1430
Broadway, New York, NY 10018.
Cutting And Welding Processes, NFPA Standard 51B, from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269.
EMF INFORMATION
The following is a quotation from the General Conclusions Section of
the U.S. Congress, Office of Technology Assessment, Biological
Effects of Power Frequency Electric & Magnetic Fields −
Background Paper, OTA-BP-E-53 (Washington, DC: U.S.
Government Printing Office, May 1989): “. . . there is now a very large
volume of scientific findings based on experiments at the cellular
level and from studies with animals and people which clearly
establish that low frequency magnetic fields can interact with, and
produce changes in, biological systems. While most of this work is
of very high quality, the results are complex. Current scientific
understanding does not yet allow us to interpret the evidence in a
single coherent framework. Even more frustrating, it does not yet
allow us to draw definite conclusions about questions of possible risk
or to offer clear science-based advice on strategies to minimize or
avoid potential risks.”
To reduce magnetic fields in the workplace, use the following
procedures:
1. Keep cables close together by twisting or taping them.
2. Arrange cables to one side and away from the operator.
3. Do not coil or drape cables around the body.
4. Keep welding power source and cables as far away as practical.
5. Connect work clamp to workpiece as close to the weld as
possible.
About Pacemakers:
The above procedures are among those also normally
recommended for pacemaker wearers. Consult your doctor for
complete information.
Considerations About Welding And The Effects Of Low Frequency Electric And
Magnetic Fields
NOTE
mod10.1 4/93
TABLE OF CONTENTS
SECTION 1 − SAFETY INFORMATION 1. . . . . . . . . . . . . . . .
SECTION 2 − SPECIFICATIONS 1. . . . . . . . . . . . . . . . . . . . .
2-1. Volt-Ampere Curves 2. . . . . . . . . . . . . . . . . . . . . . . . . . .
2-2. Duty Cycle 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SECTION 3 − INSTALLATION 3. . . . . . . . . . . . . . . . . . . . . . .
3-1. Installing Work Clamp 3. . . . . . . . . . . . . . . . . . . . . . . . . .
3-2. Installing Gas Supply 4. . . . . . . . . . . . . . . . . . . . . . . . . . .
3-3. Gun Polarity Connections 5. . . . . . . . . . . . . . . . . . . . . . .
3-4. Installing Welding Gun 6. . . . . . . . . . . . . . . . . . . . . . . . .
3-5. Connecting Input Power 7. . . . . . . . . . . . . . . . . . . . . . . .
3-6. Installing Wire Spool And Adjusting Hub Tension 9. . .
3-7. Threading And Feeding Welding Wire 9. . . . . . . . . . . .
SECTION 4 − OPERATION 11. . . . . . . . . . . . . . . . . . . . . . . . .
SECTION 5 − MAINTENANCE & TROUBLESHOOTING 13
5-1. Routine Maintenance 13. . . . . . . . . . . . . . . . . . . . . . . . .
5-2. Overload Protection 14. . . . . . . . . . . . . . . . . . . . . . . . . . .
5-3. Changing Drive Rolls And Wire Inlet Guide 5. . . . . . . .
5-4. Aligning Drive Rolls And Wire Guide 15. . . . . . . . . . . . .
5-5. Gun Maintenance 16. . . . . . . . . . . . . . . . . . . . . . . . . . . .
5-6. Troubleshooting 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SECTION 6 − ELECTRICAL DIAGRAM 17. . . . . . . . . . . . . .
SECTION 7 − PARTS LIST 18. . . . . . . . . . . . . . . . . . . . . . . . .
Figure 7-1. Main Assembly 18. . . . . . . . . . . . . . . . . . . . . . . . .
Figure 7-2. Baffle w/Components 19. . . . . . . . . . . . . . . . . . .
Figure 7-3. Wire Drive And Gears 20. . . . . . . . . . . . . . . . . . .
Figure 7-4. MWG-23B 21. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
OM-154 501 Page 1
SECTION 1 − SAFETY INFORMATION
mod1.1 2/93
Read all safety messages throughout this manual.
Obey all safety messages to avoid injury.
Learn the meaning of WARNING and CAUTION.
1 Safety Alert Symbol
2 Signal Word
WARNING means possible death
or serious injury can happen.
CAUTION means possible minor
injury or equipment damage can
happen.
3 Statement Of Hazard And Re-
sult
4 Safety Instructions To Avoid
Hazard
5 Hazard Symbol (If Available)
6 Safety Banner
Read safety blocks for each sym-
bol shown.
7 NOTE
Special instructions for best oper-
ation − not related to safety.
2
NOTE
ELECTRIC SHOCK can kill.
• Do not touch live electrical parts.
• Disconnect input power before
installing or servicing.
WARNING
READ SAFETY BLOCKS at start of
Section 3-1 before proceeding.
WARNING
5
4
6
7
1 2
CAUTION
MOVING PARTS can injure.
• Keep away from moving parts.
• Keep all panels and covers closed
when operating.
3
Turn Off switch when using high frequency.
Figure 1-1. Safety Information
SECTION 2 − SPECIFICATIONS
Table 2-1. Welding Power Source
Specifications Description
Type Of Output Direct Current/Constant Voltage (DC/CV)
Rated Weld Output 200 Amperes, 28 Volts DC, 60% Duty Cycle (See Section 2-2)
Type Of Input Power Single-Phase; 60 Hz; At 200 Or 230 Volts AC
Input Amperes At Rated Output 46 A At 200 V, 40 A At 230 V
Maximum Input Amperes While Idling 1.2 A At 200 V, 1 A At 230 V
KVA/KW Used At Rated Output 9.5 kVA/8.3 kW
Maximum KVA/KW Used While Idling 0.24 kVA/0.17 kW
Max. Open-Circuit Voltage 42 Volts DC
Control Circuit Voltage At Gun 24 Volts DC
Welding Processes Gas Metal Arc (GMAW) And Flux Cored Arc Welding (FCAW)
Calculated Speed Range At No Load 128 To 1051 ipm (3.2 To 266.9 mpm)
Wire Diameter Range .030 To .045 in (0.8 To 1.1 mm) Flux Cored Wire, .023 To .045 in (0.6 To 1.1 mm) Hard Wire
Overall Dimensions Length: 37 in (940 mm); Width: 19 in (483 mm); Height: 30-1/4 in (768 mm)
Weight Net: 225 lb (102 kg); Ship: 271 lb (123 kg)
Welding Gun
Rated Output (Air Cooled) 200 Amperes At 60% Duty Cycle Using CO
2
Shielding Gas (See Section 2-2)
Cable Length 15 ft (4.5 m)
OM-154 501 Page 2
2-1. Volt-Ampere Curves
ssb1.1 10/91 − SB-049 424-D
The volt-ampere curves show the
minimum and maximum voltage
and amperage output capabilities of
the welding power source. Curves
of other settings fall between the
curves shown.
Figure 2-1. Volt-Ampere Curves
2-2. Duty Cycle
CAUTION
WELDING LONGER THAN RATED DUTY CYCLE can damage unit or gun and void warranty.
• Do not weld at rated load longer than shown below.
wfwarn8.2 8/93
sb1.3 8/93 − SB-150 215
60% Duty Cycle At 200 Amperes
6 Minutes Welding 4 Minutes Resting
60% Duty Cycle At 200 Amperes Using CO
2
60% Duty Cycle At 180 Amperes Using Mixed Gas
Duty Cycle is percentage of 10
minutes that unit or gun can
weld at rated load without over-
heating.
0
10
Minutes
Definition
Chart
UNIT
GUN
GUN
6 minutes Welding 4 minutes Resting
6 minutes Welding 4 minutes Resting
Figure 2-2. Duty Cycle
OM-154 501 Page 3
SECTION 3 − INSTALLATION
3-1. Installing Work Clamp
1 Work Cable
2 Boot
Slide boot onto work cable. Route
cable out front panel opening from
inside.
3 Negative (−) Output Terminal
Connect cable to terminal and
cover connection with boot.
4 Hardware
5 Work Clamp
Route cable through clamp handle
and secure as shown.
Close door.
Ref. ST-800 918-B
Tools Needed:
1/2, 3/4 in
1
2
4
5
3
Figure 3-1. Installing Work Clamp
OM-154 501 Page 4
3-2. Installing Gas Supply
WARNING
CYLINDERS can explode if damaged.
• Keep cylinders away from welding and other
electrical circuits.
• Never touch cylinder with welding electrode.
• Always secure cylinder to running gear, wall, or
other stationary support.
BUILDUP OF SHIELDING GAS can harm
health or kill.
• Shut off shielding gas supply when not in use.
warn4.1 9/91
1 Cylinder Bracket
2 S-Hook
Crimp between small hole in brack-
et and chain.
3 Chain
4 Snap
Crimp onto open end of chain.
Obtain gas cylinder and chain to
running gear.
5 Cap
6 Cylinder Valve
Remove cap, stand to side of valve,
and open valve slightly. Gas flow
blows dust and dirt from valve.
Close valve.
7 Cylinder
8 Regulator/Flowmeter
Install so face is vertical.
9 Gas Hose Connection
Fitting has 5/8-18 right-hand
threads. Obtain and install gas
hose.
10 Flow Adjust
Typical flow rate is 20 cfh (cubic feet
per hour). Check wire manufactur-
er’s recommended flow rate.
Make sure flow adjust is closed
when opening cylinder to avoid
damage to the flowmeter.
11 CO
2
Adapter
12 O-Ring
Install adapter with O-ring between
regulator/flowmeter and CO
2
cylinder.
ssb3.2* 5/94 − ST-154 623 / Ref. ST-149 827-B / Ref. ST-158 697-A
Tools Needed:
5/8, 1-1/8 in
1
2
3
4
11
To Gas
Regulator/
Flowmeter
CO
2
Gas
11 12
7
5
6
5
6
7
Argon Gas Or
OR
Mixed Gases
9
8
10
Figure 3-2. Typical Regulator/Flowmeter Installation
OM-154 501 Page 5
3-3. Gun Polarity Connections
WARNING
ELECTRIC SHOCK can kill.
• Do not touch live electrical parts.
• Turn Off welding power source, and disconnect input power before inspecting or installing.
swarn1.1 2/93
1 Polarity Changeover Label
2 Wire Drive Assembly
3 Positive (+) Output Terminal
4 Negative (−) Output Terminal
Always read and follow wire man-
ufacturer’s recommended polarity.
5 Circuit Breaker CB1 (see
Section 5-2).
6 Pilot Light (see Section 5-2)
Close door.
Ref. ST-801 103-B
Tools Needed:
3/4, 11/16 in
1
2
34
5
6
Shown As Shipped − Set For Electrode
Positive (DCEP) For Solid Steel Or
Aluminum Wires (GMAW Process).
Wire Drive Assembly Lead
To Positive (+) Output Terminal
Work Clamp Lead To
Negative (−) Output Terminal
GUN POLARITY
CHANGEOVER CONNECTIONS
Reverse Lead Connections − For Electrode
Negative (DCEN) For Flux Cored Wires
(FCAW Process). Drive Assembly
Becomes Negative
S-144 449-D
Figure 3-3. Gun Polarity Connections
3-4. Installing Welding Gun
1 Wire Drive Assembly
2 Gun Securing Knob
3 Gun End
Loosen securing knob. Insert gun
end through opening until it bottoms
against drive assembly. Tighten
knob.
4 Gun Trigger Plug
Insert into receptacle, and tighten
threaded collar.
Close pressure assembly. Close
door.
Ref. ST-801 101-B
3
4
1
2
Figure 3-4. Gun Connections
OM-154 501 Page 6
Table 3-1. Electrical Service Requirements
Input Voltage
200 230
Input Amperes At Rated Output
46 40
Max Recommended Standard Fuse Or Circuit Breaker Rating In
Amperes
70 60
Min Input Conductor Size In AWG/Kcmil
8 8
Max Recommended Input Conductor Length In Feet (Meters)
89 (27) 117 (36)
Min Grounding Conductor Size In AWG/Kcmil
8 10
Reference: 1996 National Electrical Code (NEC). S-0092J
3-5. Connecting Input Power
WARNING
ELECTRIC SHOCK can kill.
• Do not touch live electrical parts.
• Turn Off welding power source, and disconnect input power before inspecting or installing.
• Have only qualified persons install unit.
• Installation must meet National Electrical Code and all other codes.
swarn3.1 2/93
A. Positioning Jumper Links
Check input voltage available at
site.
1 Jumper Links Access Door
Open door.
2 Jumper Link Label
3 Input Voltage Jumper Link
Move jumper link to match input
voltage.
Close and secure access door.
Close side door.
Ref. ST-801 100-B
Tools Needed:
3/8 in
1
2
200 VOLTS
230 VOLTS
S-153 980
3
Figure 3-5. Input Voltage Jumper Links Location
OM-154 501 Page 7
B. Connecting Input Power
Have only qualified persons make
this installation.
1 Line Disconnect Device Of
Proper Rating
2 230 Volts AC Wall Receptacle
3 Input Conductors
4 Grounding Conductor
Select size and length using
Table 3-1. Conductor rating must
comply with national, state, and
local electrical codes.
Install and connect grounding
conductor and input conductors in
conduit or equivalent between wall
receptacle and deenergized line
disconnect device.
Connect grounding conductor first,
then line input conductors.
Be sure grounding conductor goes
to an earth ground.
5 Overcurrent Protection
Select type and size using
Table 3-1. Install into deenergized
line disconnect device (fused dis-
connect switch shown).
6 Input Power Plug
Turn off unit Power switch, and con-
nect plug to wall receptacle.
ssb2.2 12/94 − Ref. ST-154 619-B / Ref. ST-149 405-B
1
4 3
5
1
3
6
34 3
For Plug Connection
2
Tools Needed:
Figure 3-6. Input Power Connections
OM-154 501 Page 8
3-6. Installing Wire Spool And Adjusting Hub Tension
Turn Off unit.
1 Wire Spool
2 Gun Contact Tip
If necessary, cut welding wire off at
contact tip, and retract wire onto
spool and secure.
3 Retaining Ring
4 Compression Spring
Remove ring and pull off spool.
Compression spring is used with 8
in (200 mm) spools.
5 Hub
6 Hub Pin
Slide spool onto hub so wire feeds
off bottom. Turn spool until hub pin
fits hole in back of spool. Reinstall
retaining ring.
7 Hub Tension Nut
Grasp spool in one hand and turn
while using a wrench to adjust hub
tension nut. When a slight force is
needed to turn spool, tension is set.
Thread welding wire (see Section
3-7). Close door.
1
2
Ref. ST-801 103-B / Ref. ST-072 573-B
Tools Needed:
3
4
5
6
15/16 in
7
Figure 3-7. Installing Wire Spool And Adjusting Hub Tension
3-7. Threading And Feeding Welding Wire
WARNING
CYLINDERS can explode if damaged.
• Keep cylinders away from welding and other
electrical circuits.
• Never touch cylinder with welding electrode.
• Always secure cylinder to running gear, wall, or
other stationary support.
ELECTRIC SHOCK can kill.
• Do not touch live electrical parts.
The welding wire, drive rolls, drive assembly, and all
metal parts touching the welding wire are electrically
live when welding or feeding wire using gun trigger.
WELDING WIRE can cause puncture
wounds.
• Do not press gun trigger until instructed to do so.
• Do not point gun toward any part of the body, other
people, or any metal when threading welding wire.
HOT SURFACES can burn skin.
• Allow gun to cool before touching.
swarn5.1 10/91 / swarn2.1 9/91
OM-154 501 Page 9
1 Wire Spool
2 Welding Wire
3 Inlet Wire Guide
4 Pressure Adjustment Knob
5 Drive Roll
6 Outlet Wire Guide
7 Gun Conduit Cable
Lay gun cable out straight.
4
7
35 621
Ref. ST-801 103-B / ST-154 251 / S-0627-A
6 in
(150 mm)
4 in
(102 mm)
Tighten
WOOD
Open pressure assembly. Pull and hold wire; cut off end. Push wire thru guides into gun;
continue to hold wire.
Close and tighten pressure
assembly, and let go of wire.
Remove gun nozzle and contact tip. Turn On.
Press gun trigger until wire
comes out of gun. Reinstall
contact tip and nozzle.
Feed wire to check drive roll pressure.
Tighten knob enough to prevent slipping.
Cut off wire. Close
and latch door.
Tools Needed:
Figure 3-8. Threading And Feeding Welding Wire
OM-154 501 Page 10
SECTION 4 − OPERATION
WARNING
ELECTRIC SHOCK can kill.
• Always wear dry insulating gloves.
• Insulate yourself from work and ground.
• Do not touch live electrical parts.
• Keep all panels and covers securely in place.
FUMES AND GASES can be hazardous
to your health.
• Keep your head out of the fumes.
• Ventilate area, or use breathing device.
• Read Material Safety Data Sheets (MSDSs) and
manufacturer’s instructions for material used.
WELDING can cause fire or explosion.
• Do not weld near flammable material.
• Watch for fire; keep extinguisher nearby.
• Do not locate unit over combustible surfaces.
• Do not weld on closed containers.
• Allow work and equipment to cool before handling.
ARCING can damage switch.
• Do not change Voltage switch position while
welding.
Arcing inside switch can damage contacts, causing
switch to fail.
ARC RAYS can burn eyes and skin;
NOISE can damage hearing.
• Wear welding helmet with correct shade of filter.
• Wear correct eye, ear, and body protection.
MOVING PARTS can cause injury.
• Keep away from pinch points such as drive rolls.
• Keep all doors, panels, covers, and guards closed
and securely in place.
MAGNETIC FIELDS FROM HIGH CUR-
RENTS can affect pacemaker operation.
• Pacemaker wearers keep away.
• Wearers should consult their doctor before going
near arc welding, gouging, or spot welding opera-
tions.
WELDING CURRENT can damage elec-
tronic parts in vehicles.
• Disconnect both battery cables before welding on a
vehicle.
• Place work clamp as close to the weld as possible.
See Safety Precautions at beginning of manual for ba-
sic welding safety information.
swarn6.2 8/92
Wear the following while welding:
1 Dry, Insulating Gloves
2 Safety Glasses With Side
Shields
3 Welding Helmet With Correct
Shade Of Filter (See ANSI
Z49.1)
sb3.1 1/94
123
Figure 4-1. Safety Equipment
DO NOT SWITCH
UNDER LOAD
WIRE MODE
VOLTAGE RANGE
FULL
LOW
HIGH
LOW
20−30V
10−20V
Ref. ST-801 103-B / S-171 601
1 Wire Mode Switch
For better control of wire speed use
Low position when wire speed is
between 90 and 670 ipm. Use Full
position when wire speed is be-
tween 150 ipm and 1030 ipm.
2 Voltage Range Selector
Place switch in desired position.
See inside rear cover for settings.
12
Figure 4-2. Center Baffle Controls
OM-154 501 Page 11
1 Wire Speed Control
Use control to set wire feed speed.
2 Voltage Control
Use control and Voltage Range Se-
lector (see Figure 4-2) to set arc
voltage. Step 6 of Low range and
Step 1 of High range overlap.
3 Pilot Light
4 Power Switch
Use switch to turn unit On and Off.
The pilot light comes on when unit
is turned on.
5 Work Clamp
Use wire brush or sandpaper to
clean metal at weld joint area.
Connect work clamp to clean,
paint-free location on workpiece, as
close as possible to weld area.
Ref. ST-154 622-B / ST-184 596 / Ref. ST-154 251
3
4
Tools Needed:
5
1
2
Figure 4-3. Controls
OM-154 501 Page 12
SECTION 5 − MAINTENANCE & TROUBLESHOOTING
WARNING
ELECTRIC SHOCK can kill.
• Do not touch live electrical parts.
• Turn Off welding power source, and disconnect
input power before inspecting, maintaining, or
servicing.
HOT PARTS can cause severe burns.
• Allow cooling period before maintaining or servicing.
MOVING PARTS can cause injury.
• Keep away from moving parts.
• Keep away from pinch points such as drive rolls.
Maintenance and troubleshooting to be performed only
by qualified persons.
swarn8.2* 2/93
5-1. Routine Maintenance
Turn Off all power before maintaining.
6 Months
Clean
Drive
Rolls
3-4
3 Months
14-Pin Cord
Gas Hose Gun Cable
− −
Replace
Cracked
Parts
Replace
Unreadable
Labels
7
Blow Out
Gun
Casing
− −
Clean
Nozzle
And Check
Contact Tip
Each Spool Of Wire
Clean
And
Tighten
Weld
Terminals3-1
See
Section
5-5
OR
Blow Out
Or
Vacuum
Inside
− −
During Heavy Service,
Clean Monthly
Figure 5-1. Maintenance Schedule
OM-154 501 Page 13
5-2. Overload Protection
READ SAFETY BLOCKS at start of
Section 5 before proceeding.
WARNING
A. Circuit Breaker CB1
Ref. ST-801 103-B
1 Circuit Breaker CB1
2 Pilot Light
If CB1 opens, pilot light goes out,
and wire feed stops. Check gun lin-
er for blockage or kinks, and check
for jammed wire, binding drive gear,
or misaligned drive rolls. Allow a
cooling period before resetting
CB1.
2
1
Figure 5-2. Circuit Breaker CB1
B. Fuses F1 And F2
Turn Off unit and disconnect input
power.
1 Fuse F1 (See Parts List For
Rating)
F1 protects the 115 volts ac winding
of transformer T1. If F1 opens, all
weld output stops and pilot light PL1
goes out.
2 Fuse F2 (See Parts List For
Rating)
F2 protects the 24 volts ac winding
of transformer T1. If F2 opens, all
weld output stops.
Ref. ST-800 928-B
2
1
Figure 5-3. Fuse Location
C. Overheating
0
15
minutes
When overheated, thermostat
opens, output stops, and cooling
fan keeps running.
Let fan run for
15 minutes.
Start welding.
ssb10.1 1/94 − Ref. ST-157 072-A
Figure 5-4. Overheating
OM-154 501 Page 14
5-3. Changing Drive Rolls And Wire Inlet Guide
ST-150 227-C
1 Securing Screw
2 Inlet Wire Guide
Loosen screw. Slide tip as close to
drive rolls as possible without
touching. Tighten screw.
3 Anti-Wear Guide
Install guide as shown.
4 Drive Roll
Install correct drive roll for wire size
and type.
5 Drive Roll Securing Nut
Turn nut one click to secure drive
roll.
1
3
2
4
5
5/64 in
7/16 in
Tools Needed:
Figure 3-9. Changing Drive Rolls And Wire Inlet Guide
5-4. Aligning Drive Rolls And Wire Guide
READ SAFETY BLOCKS at start of
Section 5 before proceeding.
WARNING
Y Turn Off unit.
View is from top of drive rolls look-
ing down with pressure assembly
open.
1 Drive Roll Securing Nut
2 Drive Roll
3 Wire Guide
4 Welding Wire
5 Drive Gear
Insert screwdriver, and turn screw
in or out until drive roll groove lines
up with wire guide.
Ref. ST-800 412-A
Correct Incorrect
5
4
3
2
6
Tools Needed:
Figure 5-5. Aligning Drive Rolls And Wire Guide
OM-154 501 Page 15
5-5. Gun Maintenance
READ SAFETY BLOCKS at start of
Section 5 before proceeding.
WARNING
FLYING METAL CHIPS AND DIRT can cause injury and damage equipment.
• Point gun away from people and in a safe direction when blowing out with compressed air.
swarn10.1 10/91
Turn Off unit and disconnect input
power.
1 Wire Spool
Cut welding wire off at contact tip.
Retract wire onto spool and secure.
2 Gun Securing Knob
Loosen knob and remove gun and
trigger plug.
Reassemble gun.
To Reassemble Gun:
Install contact tip.
Insert new liner.
Install collet onto liner and tighten
into gun/feeder connector using
wrench.
Cut liner off near collet so that liner
end is as close to drive rolls as pos-
sible without touching.
Install nozzle.
Reinstall gun (see Section 3-4).
Thread welding wire (see Section
3-7). Close door.
Ref. ST-801 101-B / ST-801 149
Tools Needed:
3/8 in
1
2
3/8 in
Head Tube
3/8 in
Remove nozzle,
contact tip, and
liner collet.
Blow out
gun casing.
Gun/Feeder
Connector
Remove liner.
Figure 5-6. Gun Maintenance
OM-154 501 Page 16
5-6. Troubleshooting
READ SAFETY BLOCKS at start of
Section 5 before proceeding.
WARNING
Welding Trouble Remedy Section
No weld output; wire does not feed. Secure power cord plug in receptacle. 3-5
Reset circuit breaker CB1. Replace fuse F1 and/or F2. 5-2
Replace building line fuse or reset circuit breaker if open. 3-5
Secure gun trigger plug in receptacle or repair leads, or replace trig-
ger switch.
3-4
No weld output; wire does not feed; fan
motor continues to run and pilot light is
off.
Thermostat open (overheating). Allow fan to run; the thermostat will
close when the unit has cooled.
5-2
No weld output; wire feeds. Connect work clamp to get good metal to metal contact. Figure 4-3
Replace contact tip. 5-5
Low weld output. Connect unit to proper input voltage or check for low line voltage. 3-5
Wire Drive/Gun Trouble
Electrode wire feeding stops during
welding.
Straighten gun cable and/or replace damaged parts. 5-5
Adjust hub tension. 3-6
Adjust drive roll pressure. 3-7
Replace contact tip if blocked. 5-5
Clean or replace wire inlet guide or liner if dirty or plugged. 5-4, 5-5
Replace drive roll or pressure bearing if worn or slipping. 5-4
Secure gun trigger plug in receptacle or repair leads, or replace trig-
ger switch.
3-4
Check and replace F1 and/or F2. 5-2
Check and clear any restrictions at drive assembly and liner. 5-4, 5-5
Have nearest Factory Authorized Service Station check drive
motor.
− −
SECTION 6 − ELECTRICAL DIAGRAM
SB-174 099-B
Figure 6-1. Circuit Diagram For Welding Power Source
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Miller MW250 Owner's manual
- Category
- Welding System
- Type
- Owner's manual
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