Trouble Shooting And Repairs; Spare Parts - Nomenclature - MarelliGenerators MJB 250 Instructions

6. TROUBLE SHOOTING AND REPAIRS

TROUBLE
The alternator will not
energise (no load voltage
below 10% of rated
voltage).
The alternator will not
energise (no load voltage
20-30% of rated voltage).
Voltage insensitive to AVR
potentiometer's rotation.
Voltage lower then rated
(output voltage between
50 and 70%).
Voltage too high.
Unstable voltage.
7.SPARE PARTS NOMENCLATURE
Part name
Pos.
201 D side (D:E) bearing
202 N side (N.D.E.) bearing
6 Voltage regulator
7 Fuse (6.3x32 10A – 500V)
309 Rotating diode (inverse)
310 Rotating diode (direct)
311 Surge suppressor
119 Complete rotating rectifier
POSSIBLE CAUSE
a) Loose connections.
b) Rotating diodes or surge suppressor
broken.
c) Excitation circuit shorted or interrupted.
d) Insufficient residual voltage
a) Fuse (on AVR's supply line) blown.
b) Connection's cut on the exciter stator.
c) Incorrect connections of exciter stator.
a) Speed less than rated.
b) Voltage potentiometer unset.
c) Fuse blown.
d) Faulty regulator.
e) Overexcitation limitation intervention.
a) Potentiometer V unset.
b) Faulty regulator.
a) Diesel engine rpm variations.
b) Stability potentiometer unset.
b) Faulty regulator.
Type / Code
MJB 250
6218 C3 / 346110114
6313 2Z C3 / 346114065
41 HFR 80 / 963821112
41 HF 80 / 963821113
M16FA864A
M25FA648B
21
REMEDY
(always to be done with the machine switched off)
a) Check and repair.
b) Check the diodes and change in case they are open or
shortcircuited.
c) Check the continuity and repair.
d) Apply for a while a 12 Volt battery voltage connecting
the – terminal to – of AVR and + terminal to + of AVR by
means of a diode.
a) Replace the fuse with the spare. If the fuse blows again
check if the exciter stator is short circuited. If everything is
correct, change the AVR .
b) Check the continuity and repair.
c) Reverse the two wires from the exciter stator.
a) Check rpm (frequency).
b) Rotate the potentiometer until the voltage reaches the
rated value.
c) Replace the fuse with spare.
d) Disconnect AVR and replace it.
e) Re-set the potentiometer for excitation limitation (AMP)
a) Rotate the potentiometer until the voltage reaches the
rated value.
b) Replace AVR.
a) Check rpm uniformity. Check the diesel engine
governor.
b) Act on AVR's stability potentiometer.
b) Replace AVR.
MJB 315
6319 C3 / 346151095
6315 2Z C3 / 346114075
MARK I M40FA640A/A
963823010
71 HFR 120 / 963821170
71 HF 120 / 963821171
21
ENGLISH
MJB 355
6322 C3 / 346151110
6317 2Z C3 / 346114085
M40FA990A
M40FA500A