Toro Greensmaster 3120 Service Manual page 215

Identifying the Diodes and their Functions
Testing the Diodes
Greensmaster 3120
17230SL Rev C
The main wiring harness contains six (6) diodes. The diodes are used for circuit
protection from inductive voltage spikes and for safety circuit logic. Diodes D1-A,
D1-B, D1-C and D1-D are attached to a circuit board that plugs into the main
wire harness located under the control panel shield ;refer to
D2 and D3 are individual plug-in diodes connected to the main harness near the
front of the mower hydraulic manifold.
Diode D1-A allows the engine to start only with the function control lever in the
N position (neutral switch closed). The diode also allows the engine to
EUTRAL
continue to run with either the function control lever in the N
the operator sitting in the seat (seat switch closed).
Diode D1-B prevents a negative voltage spike from damaging the neutral switch
and seat switch by allowing a path to ground for the start safety relay (K2)
when it de-energizes.
Diode D1-C maintains current flow to the joystick relay (K3) after the joystick is
released from the L
OWER
Diode D1-D prevents a negative voltage spike from damaging the mow and
backlap switches by allowing a path to ground for the mow relay (K4) when it
de-energizes.
Diode D2 prevents current flow to solenoid valve coil S4 when solenoid valves
S2 and S3 are energized through by the raise relay (K6).
Diode D3 prevents current flow to solenoid valve coil S3 when solenoid valves
S2 and S4 are energized through by the lower relay (K5).
1. Park the machine on a level surface and lower the cutting units. Make sure
the engine is off and the key switch is in the OFF position.
2. Access the diode to be tested and disconnect the diode from the main wire
harness.
3. Use a multimeter (ohms setting) and check the continuity across the diode
terminals in both directions; refer to the
Note: If diodes D1-A, D1-B, D1-C or D1-D are damaged, the entire circuit
board should be replaced.
4. Replace the diode if necessary.
5. If the diode tests correctly and a circuit problem still exists, check the wire
harnesses; refer to
Note: Apply dielectric gel to the circuit board contacts whenever the circuit
board is installed into the wire harness; refer to
6. Connect the diode(s) to the wire harness before returning the machine to
service.
position (joystick lower switch opens).
Diode Testing Reference (page
Appendix A (page A–1).
Page 5–29 Electrical System: Testing the Electrical Components
Figure 95. Diodes
position or
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Dielectric Gel (page 5–4).
5–28).