John-deere stx38 User Manual download pdf (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.

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John-deere stx38 User Manual Page 110

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