John Deere stx38 - Manual (Page 110)

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3/21/97
CIRCUIT OPERATION AND DIAGNOSIS ELECTRICAL
CIRCUIT OPERATION AND
DIAGNOSIS
CRANKING CIRCUIT OPERATION
STX30 & STX38 (SN —210000)
Function:
The cranking system is used to energize the starting
motor.
Operating Conditions:
In order to crank the engine; the key switch must be in
the START position, the PTO switch must be OFF, and
the transaxle must be in neutral. The operator DOES
NOT have to be on the seat to crank the engine.
Theory of Operation:
For units up to (SN —160000) the starting motor is a
solenoid shift design. For units (SN 160001— ), the
starting motor has a separate starter solenoid. Current
flows from the battery (G1) positive terminal to the
starter solenoid (K1) battery terminal, fusible link or
circuit breaker (F1), and key switch (S1) in the START
position, current flows to the PTO switch (S2).
The PTO switch is used in the neutral start circuit to
prevent the engine from cranking if the PTO is
engaged. With the PTO switch closed (PTO
disengaged), current flows to the neutral start switch
(S3).
The neutral start switch is located in the top of the
transaxle directly over the shift fork. When the shift fork
is in the neutral position, the switch is closed. The
neutral start switch is used to prevent the engine from
cranking if the transaxle is in gear. With the neutral
start switch closed, current flows to the key switch
S1—S2 terminals and starter solenoid, engaging the
solenoid. The solenoid is engaged by current flowing
through both pull-in and hold-in windings, pulling the
plunger inward. The plunger closes the solenoid main
contacts. When the main contacts are closed, both
ends of the pull-in windings have the same voltage so
current through the pull-in windings stops. Current
continues through the hold-in windings, keeping the
solenoid engaged.
With the solenoid main contacts closed, high current
from the battery flows across the main contacts to the
starter motor (M1) causing it to turn.