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SEN00794-02
H-5 Boom speed or power is low
Failure
• Boom speed or power is low
phenomenon
• The normal mode is the state that the heavy lift switch, swing priority switch, and machine push-up
switch are turned OFF.
• Check that the other work equipment, travel, and swing are normal. (If any of them is abnormal, carry
Relative
out troubleshooting related to it.)
information
• Check that the machine does not deviate. (If it deviates, carry out troubleshooting related to deviation.)
• When carrying out the following troubleshooting, set the working mode in the P-mode.
• Before carrying out troubleshooting, check that electric circuit related to boom control is normal.
Malfunction of right PPC
1
valve (Boom circuit)
Malfunction of swing
2
priority solenoid valve
Possible causes
and standard
value in normal
state
Malfunction of boom
3
control valve (spool)
Malfunction of boom
4
control valve
(Safety-suction valve)
Boom control valve
5
(control valve unit)
defective
Boom cylinder seal defec-
6
tive
14
Cause
Standard value in normalcy and references for troubleshooting
aKeep the engine stopped for the preparations, and run it at high idle
during troubleshooting.
Right work equipment control lever
Boom RAISE/LOWER stroke end
aKeep the engine stopped for the preparations, and run it at high idle
during troubleshooting.
Swing priority switch and
right work equipment control lever
Swing priority switch OFF +
Swing priority switch ON +
Boom RAISE operation
The spool of the boom control valve (Lo, Hi) may malfunction. Check it
directly.
The safety-suction valve of the boom control valve (Lo) may malfunc-
tion. Check it directly. (When checking the safety-suction valve by
exchanging it with a valve of another work equipment circuit, stop the
hose of the machine push-up solenoid securely. After finishing check, be
sure to return the safety-suction valve since its set pressure and struc-
ture are different from others.)
The control valve unit of the boom control valve (Lo, Hi) may be defec-
tive. Check it directly.
aKeep the engine stopped for the preparations, and run it at high idle
during troubleshooting.
Right work equipment control lever
(1) The boom speed or power is low in the normal
mode.
Lever in neutral
Boom RAISE relief
40 Troubleshooting
PPC valve output pressure
+0.8
2.9
MPa
–0.2
+8
{30
kg/cm
2
}
–2
Solenoid valve outlet pressure
0 MPa {0 kg/cm
2
}
+0.8
2.9
MPa
–0.2
+8
{30
kg/cm
2
}
–2
Leakage from cylinder
Max. 20 cc/min
PC800, 850-8
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Troubleshooting
