Miller Electric S-21E - Manual (Page 18)

SECTION 8— TROUBLESHOOTING
A
8-1. TESTING INSTRUMENTS AND INFORMA-
TION
The service procedures in this manual require proper
testing instruments. Use a good quality digital volt-
ohmmeter (DVM) with one megohm input impedance or
greater and diode check capability (use an analog VOM
for variable resistor testing). If an oscilloscope is speci-
fied, use a good quality unit with one megohm input im-
pedance or greater. If a circuit board has a protective
coating, it will be necessary to remove coating or use
needle probes in the test area to obtain proper contact.
Recoat areas if necessary to retain corrosion protection.
Digital volt-ohmmeters (DVM’s) do not require lead po-
larity attention when making connections. However, the
meter may indicate a — (negative) voltage when the test
procedure specified a + (positive) voltage. If the incor-
rect polarity appears on the display, reverse meter lead
connections to test points.
8-2. CIRCUIT BOARD HANDLING PRECAUTIONS
WARNING: ELECTRIC SHOCK can kill.
• Do not touch live electrical parts.
• Shut down wire feeder and welding power
source, and disconnect input power employ-
ing lockout/tagging procedures before
inspecting, maintaining, or servicing.
Lockout/tagging procedures forwirefeedercon-
sist of disconnecting interconnecting cord, and
for welding power source consist of padlocking
line disconnect switch in open position, remov-
ing fuses from fuse box, or shutting off and red-
tagging circuit breaker or other disconnecting
device. Stop engine, and disconnect negative
(—) battery cable from battery on welding gen-
erators.
MOVING PARTS can cause serious injury.
• Keep away from moving parts.
HOT SURFACES can cause severe burns.
• Allow cooling period before servicing.
CAUTION: ELECTROSTATIC DISCHARGE
(ESD) can damage circuit boards.
• Put on properly grounded wrist strap
BEFORE handling circuit boards.
• Transport circuit boards in proper static-
shielding carriers or packages.
• Perform work only at a static-safe work area.
INCORRECT INSTALLATION or misaligned
plugs can damage circuit board.
• Be sure that plugs are properly installed and
aligned.
EXCESSIVE PRESSURE can break circuit
board.
• Use only minimal pressure and gentle move-
ment when disconnecting or connecting
board plugs and removing or installing board.
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8-3. TROUBLESHOOTING (Table 8-1 And Dia-
gram 8-1)
A WARNING: ELECTRIC SHOCK can kill.
• Do not touch live electrical parts.
• Shut down wire feeder and welding power
source, and disconnect input power employ-
ing lockout/tagging procedures before
inspecting, maintaining, or servicing.
Lockout/tagging procedures forwire feeder con-
sist of disconnecting interconnecting cord, and
for welding power source consist of padlocking
line disconnect switch in open position, remov-
ing fuses from fuse box, or shutting off and red-
tagging circuit breaker or other disconnecting
device. Stop engine, and disconnect negative
(—) battery cable from battery on welding gen-
erators.
MOVING PARTS can cause serious injury.
• Keep away from moving parts.
HOT SURFACES can cause severe burns.
• Allow cooling period before servicing.
Troubleshooting to be performed only by
qualified persons.
The troubleshooting table is designed to diagnose some
of the troubles that can develop in this wirefeeder. Any
circuit normally tied to ground must be at ground poten-
tial.
Use the table in conjunction with the diagrams in this
manual and the exploded views and component values
in the Service Parts Manual while performing tro-
ubleshooting procedures.
When replacing components, use only genuine MILLER
replacement parts. MILLER parts are required for war-
ranty repair by authorized warranty service agency.
Resistance and continuity measurements must be
made with the unit shut down. Isolate components be-
fore making resistance and continuity measurements.
IMPORTANT: Beforebeginning troubleshootingproce-
dures, visually examine internalcomponents forsigns of
overheating and failure. Many majorproblems, such as
winding(s) failure are usually apparent bydiscoloration,
smoke, and smell. Fortunately most electricalproblems
are relatively simple: blown fuses, trippedcircuit break-
ers, incorrect switch positions, loose connections, cor-
rosion, and the like. A complete, careful inspection often
saves considerable time, money and frustration.
IMPORTANT: Be sure that all connections are correct
and secure according to Section 4 and that all controls
and switches are in proper positions before proceeding
with troubleshooting.
TM-1571 Page 14 S-21E