Oshkosh JLG 400S, Service And Maintenance Manual

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SECTION 3 - CHASSIS & TURNTABLE
3-94 – JLG Lift – 3120895
No Output on Weld Receptacle but AC
Receptacle Output OK
If you have no welding power at all but the AC (120 volts)
is fully operational, this could be caused by three compo-
nents.
a. The welding impedance (transformer).
b. The stator windings.
c. The main welding rectifier bridge.
Using the electrical diagram check for continuity of the
welding impedance (transformer). By disconnecting the
three heavy lead wires from the main welding bridge recti-
fier, you can check continuity between those three wires.
In any combination, the resistance should be between
one and two ohms. All three readings should be the same.
If you have readings that determines that the stator wind-
ing and impedance winding are in good condition. With
the three wires removed, you can now check resistance of
the main Rectifier Bridge. By measuring resistance
between the three terminals forward and reverse you
always should get a high and low reading, for example; if
you measure between one and two, if the first reading is
very high the reverse reading should be very low. You can
also check the bridge by taking a resistance reading on
the main welding terminals. Again, you should have a high
and low reading by reversing the leads.
Welder Completely Dead - No AC or Weld
Power
Make sure welder is at proper speed = 3600RPM. Unplug
all external connections. A shorted weld cable or genera-
tor accessory plugged in can cause the welder not to
build up. Several components can cause the welder to
stop functioning completely. This is mainly in the excita-
tion circuit. Consisting of the armature (rotor), excitations
bridge (left bottom corner) and auxiliary winding. Check
the resistance of the auxiliary winding by removing the two
purple wires from the Excitation Bridge located at the left
bottom corner. THe reading should be about 1.5 ohms.
Check the resistance of the armature between the two slip
rings, this should be 22 ohms. Remove all wires for the left
bottom Rectifier Bridge and test for continuity between ter-
minals. Again, you should get a high and low reading. If
those three main components test ok, try to flash the
armature with a 24 volts circuit (previously explained).
Intermittent Welder Operation
Welder works properly for a few minutes and then stops
operating but returns to full welding power after several
minutes of cooling off.
This will occur when the welder is operated past its duty
cycle or in extreme high ambient temperatures or if welder
cooling circuit is blocked. Be sure air intake is mount to
receptacle panel. Allow fresh air to enter louvered end
cover on welder. A cooling off period of 4-5 times longer if
welder is turned off and sitting still. Running it at its RPM
will speed up the cooling and reset the internal trip.