Onan MJA Series Service Manual page 125

12.3
,~
CONTROL SYSTE M
down the plant.
If
the plant doesn't
shut down, check both coils with an
ohmmeter. Resistance of each
should be 50 ohms. If the relay
won't latch, check the contacts in
series wlth Coil B.
c. Emergency relay MJA and 5MJB
(Begin Spec F) - See Sect 6. 3.3.4
d. Centrifugal switch - The centrif ­
ugal switch is open when the plant
is stopped. During the starting
cycle, it closes when the plant
speed reaches about 900 rpm.
The gap, with the plant stopped
should be maintained at .020 in.
,.1
~I
L
FIG 6. C - LOW OIL PRESSURE
LATCHING RELAY
For a complete description and repair instructions, see Sect. 3.3.2.3
and 6. 3.
1.
4.
6.3 TESTING AND REPAIR
MODELS: 705 MJB-R, MJC-R
The control systems of these models use a separate starting motor and
a rectifier and alternator battery charging system. A separate winding
in the generator acts as battery charging alternator (see Sect. 4.3.2.3).
Optional high temperature cut-off and low oil pressure cut-off circuits
are available. On the MJB-R and MJC-R (Revolving Field Models), an
engine mounted centrifugal switch serves as start-disconnect.
If
any component of the control circuit fails, replace it. Normally
it isn't worth-while to attempt repair of relays etc. If relay contacts
are dirty, they can be cleaned by pulling hard paper. or gauze soaked
in carbon tetracloride.between the contacts.
6.3.1 STARTING AND STOPL>,G SYSTEM. - The starting system in ­
cludesstart ignition relaY,ignition relay, startillgs01enoid, and the
centrifugal switch.
It
controls the solenoid-shift, over-running clutch,
starting motor and the ignition coil circuit. Fig 6. D shows the start
cycle.
To stop the engine, the stop switch grounds the ignition relay, which
opens the circuit to the ignition coil.
6.3.1.1 Start Ignition Relay (#307B597). - This relay, with metal cover,
is energized at the beginning of the start cycle by the start switch.
It
de-energizes when the centrifugal switch closes, completing the start
cycle.