Lincoln Electric SHIELD-ARC 500AS Operating Manual page 11

READ IN CONJECTION WITH WIRING DIAGRAM AM3064MC on Page 18
TROUBLE
Machine fails to start
Machine starts but has
the following faults:
Voltage at AC outlet but
no voltage or reduced
voltage at welder output
studs.
There is not output from
either the AC outlet or
the welder output studs.
Machine has low welding
output or fails to hold
welding current constantly.
IMA 551C
TROUBLESHOOTING
CAUSE
Check for:
Flat battery and/or faulty terminal connections.
Key switch (4) faulty connection and/or loose wires.
Starter Motor faulty (21).
Check DC voltage across bridge rectifier (8). If there is
no voltage or half voltage, bridge rectifier may have
open circuit in one or two diodes only.
If the above is O.K., then check:
Rheostat (9) for open circuit
Shunt coil (9A) for open circuit
Bad connections
Field reversing switch (20) faulty
Check fuses F1 and F4
If F4 is blown also check bridge rectifier (8).
If the above are O.K., then check flashing circuit for
faults. Check there is battery voltage across rotor
brushes (12A) with key switch (4) turned midway
Between "On" and "Start" positions
If not check for:
Bridge rectifier (10,11) open circuit
Key switch (4) faulty
Poor connections
If the above are O.K., then check for:
Alternator brushes (12A) sticking or excessively
worn
Dirty slip rings (12A)
Bridge rectifier (8) open or short circuited
Rotor (12) open or short circuit (rotor resistance
approximately 11ohm
Stator field windings (17) open or short circuit.
Capacitors (13) faulty
Poor connections
Rectifier bridge (8) and (10,11) may be open circuited on
one or two diodes only.
Rotor (12) or brushes (12A) may have a ground
Engine speed low
Main brush holder rocker (7) moved position
Commutator may be dirty (7A)
Two segments on commutator (7A) burnt (open in that
coil)
Short circuit in armature (7A) 2 segments burnt in four
locations 90° apart)
Main brushes excessively worn (7)
Faulty capacitors (13)
Brush springs may be broken (7)
Field circuit may have variable resistance connections or
intermittent open circuit, due to loose connections or
broken wires (17), (8), (9) or (9A)
Electrode lead or work lead connections may be poor
Wrong grade of brushes may have been installed on
generator (7)
Field rheostat may be making poor contact and over-
heating (9)
Current-adjusting mechanism may not be operating
properly (5A)
Current control brush holder contact springs may be worn
out or missing. Contact surface may be dirty, rough or
pitted (5a)
Current control brush holder support stud and mating
contact surfaces may be dirty or pitted and burned (5A)
WHAT TO DO
Charge battery and/or clean terminals.
Repair or replace
Repair or replace
Replace
Replace
Repair or replace
Repair
Repair or replace
Replace
Replace
Replace
Replace
Repair
Free or Replace
Clean
Replace
Repair or replace
Repair or replace
Replace
Repair
Replace bridge
Locate and remove ground
No load 1780 rpm, Full load 1700 rpm
Realign drilled marker points
Refer maintenance section (page 5)
Repair or replace
Locate fault using growler and repair or replace
Replace brushes
Replace capacitors
Replace brush springs
Check field current with ammeter to discover varying
current. This applies to both the main
generator and alternator
Tighten all connections
Fit correct Lincoln brushes
Inspect rheostat. Clean out and if necessary increase
finger tension on contact arm by bending arm
Check for loose or missing set screw in control handles
Inspect. Replace needed parts. Clean internal contact
surface of control device. Do not lubricate. Smooth up
roughened surface.
If brush holder internal contact surface is pitted and
burned, replace the brush holder and support stud. If
the contact surface is dirty, clean off the brush holder
stud and internal contact surface. Apply mixture of
three parts of silicone grease and one part zinc powder
(by weight) to stud
500AS Page 11