Lincoln Electric SHIELD-ARC 500AS, Operating Manual

Page: 10 / 21

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