Craftsman 28906, Professional Shop Manual

Page 1: ...an be accepted for any inaccuracies or omission in this publication although care has been taken to make it as complete and accurate as possible at the time of publication However due to the variety of outdoor power equipment and continuing product changes that occur over time updates will be made to these instructions from time to time Therefore it may be necessary to obtain the latest materials ...

Page 2: ... Park brake switch 14 Reverse Safety Switch 14 Seat Safety Switch 15 Starter solenoid 16 Fuse 17 Electrical diagnosis 17 Electrical environment AC Vs DC 19 Types of circuits 21 Series 21 Parallel 21 Series parallel 22 Shorts 22 Opens 22 Increased resistance 22 The Tools 22 Equipment that may be useful 22 Digital Multi meter 23 Wiring diagram or schematic 24 Fused jumper wires 24 Test lights high i...

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Page 4: ...t points indicate sub steps or points Disclaimer This Professional Shop Manual is intended for use by trained professional technicians Common sense in operation and safety is assumed In no event shall MTD be liable for poor text interpretation or poor execution of the proce dures described in the text If the person using this manual is uncomfortable with any procedures they encounter they should s...

Page 5: ...e serial number reads as follows 1 engineering level J month of production J October 05 day of the month 0 last digit of the year H plant it was built in 3 assembly line number 0003 number of unit built Precautions CAUTION Before disconnecting any electrical component take precautions to prevent the component or the wires attached to it from short ing out The most effective means of doing this is ...

Page 6: ...conversion to fuel injection in the 1980s NOTE The starter safety circuit has no connec tion to the RMC module The only one switch in the safety circuit that is capable of turning off the engine works through the RMC module It is still important to be familiar with the workings of the individual components of the electrical system but some of them can now be checked from a central point on the tra...

Page 7: ...t age Then check for power where the fused red wire with white trace connects to the B terminal Check for continuity between B and S terminals in START position If power is getting to the S terminal in the START position the problem lies down stream in the starter circuit Check conti nuity from the orange wire on the S terminal to the orange wire with white trace on the trigger spade on the starte...

Page 8: ...ng brake is set To re arm the module the key is moved to another position breaking the ground signal then returned to the REVERSE CAUTION MODE re establishing the ground signal It works some thing like a latched relay If it is not possible to break the ground path it is not possible to freshly establish it either and the RMC module will not be armable Causes for such a condition might include a sh...

Page 9: ... the RMC mod ule is faulty The RMC plug test will give an indication of what the problem is if it is not a faulty RMC module If the problem is identified in a particular circuit check the safety switch that is associated with that circuit If the switch is good then the prob lem lies within the wiring harness NOTE Like the electronic components found on most cars the RMC module requires a fully cha...

Page 10: ...he RMC module or in the PTO switch circuit Bottom left middle rounded shape Yellow wire Behavior When the terminal is probed yellow wire there should be continuity to ground only when the seat is empty Circuitry The yellow wire leads to the seat safety switch where it finds a path to ground when the seat is empty Interpretation If behavior is correct the seat safety circuit is good If there is con...

Page 11: ... for a blown fuse or a bad key switch Bottom right middle rounded shape The DurDle wire provides a ground signal to the RMC mod ule when the key switch is placed in the REVERSE CAUTION MODE Behavior There should be continuity to ground at this terminal when the key switch is in the REVERSE CAUTION MODE position Circuitry When the key switch is in the REVERSE CAUTION MODE position a ground path is ...

Page 12: ... the key switch is off or there may be a short to ground in the wire leading to it If there is not continuity to ground when the seat is empty the switch may be inoperative or there may be an open condi tion in the wire leading to it Top right middle square shape There is a red wire with black trace between yellow wire and the green wire This wire provides the module with input from the reverse sw...

Page 13: ...g ground or a shorted reverse safety switch Lack of continuity to ground would indicate A broken or disconnected wire leading to the brake or park brake switches A switch that is not closing because of physical damage or corrosion Loss of ground to the park brake switch Bottom right middle rounded shape The white wire provides a ground signal to the RMC mod ule when the key switch is placed in the...

Page 14: ... and the middle terminals are nor mally open at rest NOTE There are three contacts on the right side in the C COM For this application the normally opened NO contact is used PTO relay The PTO relay is located on the main harness under neath the electric PTO switch See Figure 7 10 Figure 7 10 The PTO relay has 5 wire going to it The red wire is battery power from the A1 termi nal of the key switch ...

Page 15: ...empty or an unsafe condition is sensed by the RMC module a ground signal is sent to the PTO switch If the PTO is on the ground signal will pass through the switch and go to the ignition module turning the engine off A NC PoleB NO PoleC NO Figure 7 12 The plunger on the switch is depressed when the clutch brake pedal is pressed down de clutching the drive belt and applying the brakes The switch con...

Page 16: ...n de clutching the drive belt and applying the brakes The switch contains two sets of contacts The brake switch is accessed by removing the fender and dash The fender and dash can be removed by following the steps described in Chapter 4 Body Chassis A normally open NO set of contacts is in the starter inhibit circuit When the clutch brake pedal is depressed the contacts are closed power coming fro...

Page 17: ...rake pedal is depressed and the parking brake is set a ground signal will pass from the park brake switch through the brake switch to the RMC module Reverse Safety Switch The Reverse Safety Switch is a simple metal contact tang switch CVT transmissions Tractors that have the CVT transmissions have the reverse switch mounted on the left side of the frame by the rear wheel When the tractor is placed...

Page 18: ...is connected to the safety circuit When the seat is vacant the switch closes creating a ground path in series with the brake switch If the brake is OFF and the seat is empty the circuit is completed short ing out the primary windings of the ignition mod ule turning off the engine On tractors with an electric PTO the yellow wire connected to the seat safety switch sends a ground signal to the RMC m...

Page 19: ...d can be accessed by removing the battery box and reaching through the opening See Figure 7 22 Figure 7 22 Figure 7 23 The red wire carries battery power the green wire is a ground When the proper safety conditions are met brake applied PTO OFF the oran qe wire with white trace energizes the windings that magnetize an iron core pulling the contacts closed between the two heavy posts connecting bat...

Page 20: ...d but the remaining 20 of the diagnoses are the really difficult ones that can devour the same amount of time as the easy 80 Experience plays a big part in successfully diag nosing the really difficult electrical problems Experi ence leads to greater understanding Two German Physicists working independently during the late 18th and early 19th centuries summarized what they had figured out about el...

Page 21: ...he igni tion system on a fiberglass bodied Corvette and filtering devices built into vulnerable compo nents Something as simple as putting non resistor spark plugs in a machine with electronic controls can disable the controls Voltage Spikes A dramatic increase in voltage will damage many electronic devices Such spikes may be caused when jumper cables are disconnected or a voltage regulator fails ...

Page 22: ...hort The capital letter T is used to represent Amps Ohms Resistance Resistance is the opposition to current flow It is a restriction that slows down the flow of current Resistance is measured in Ohm s The greek letter omega W or the letter R for Resistance is used to represent Ohm s Resistance creates heat A circuit with too much electrical load or too much resistance for the load placed on it wil...

Page 23: ...tage law deals with voltage drops A voltage drop is the amount of voltage used up or dropped by resistance in a circuit Ohm s law states that V IxR every component in a circuit has resistance even the wires To push current through resistance it takes voltage Kirchhoff s voltage law states that the sum of all the voltage drops equals the source voltage As an example imagine a circuit that has a 12V...

Page 24: ... on the frame should be the same as the negative post of the battery Electrically unless there is a bad connection between the battery and the frame or between the frame and the component or cable that is assumed to be grounded to it 7d Most circuits have additional components like switches and fuses Types of circuits There are three ways a circuit can be wired Series Parallel Series parallel Seri...

Page 25: ... caused by loose or cor roded connections or connections that are insu lated by grease paint or coatings Fasteners finished in oil phosphate or black oxide are bad conductors Use bright fasteners zinc coated Resistance can be a problem on the ground side as well as the hot side of a system remember that electricity must complete a loop circuit back the battery post Any resistance in that loop will...

Page 26: ... meter Some meters have an inductive Amp clamp accessory that can be used without breaking the circuit Testing amperage beyond the capacity of the meter can burn out an internal fuse in some meters The fuses can be expensive Resistance Set the meter for the W scale Isolate the part of the circuit to be tested discon nect it from the source of power Ohms are read on a scale of 0 to 1 with 0 indi ca...

Page 27: ...use a test light on a 900 series tractor It can damage the RMC module Figure 7 32 Some high impedance test lights are capable of indicating whether the current being sampled is AC or DC Battery Jumper Cables The obvious use jumper cables can be used to jump start equipment to get it into the shop This is not recommended for any fuel injected Kohler powered equipment The clever use If the technicia...

Page 28: ...perage systems while part 19468 tests higher amperage systems See Figure 7 34 Kohler makes a proprietary Rectifier Regulator tester Kohler Part Number 25 761 20 and the up dated version 25 761 20 S This tester works on Kohler regulator rectifiers and the company claims it works on similar systems from other companies See Figure 7 35 Instructions are included with the Kohler tool TT480 A Usage of t...

Page 29: ...will be necessary to compare it to the engine manufacturer s specified out put This varies from model to model la With a DMM set to read AC Voltage con nect the probes between ground and one of the AC wires of the stator lb Leave the regulator rectifier connected to the harness lc Start the engine and run it at the RPM specified by the engine manufacturer ld Read the voltage on the meter le If the...

Page 30: ...d A fixed load battery tester can be used to apply enough load to test the charging system out put Batteries 1 Precautions See Figure 7 39 CAUTION Batteries produce flammable and explosive gases particularly during charging Figure 7 39 Do not smoke or allow an open flame or heat source near the battery Charge batteries in an open area Wear eye protection and acid resistant gloves when handling bat...

Page 31: ...gher than 2 amps Damage to the battery will result CAUTION Never attempt to charge or jump a frozen battery 30 Charge the battery until it is fully charged Most battery chargers have an amp gauge to show the charging rate When the gauge is at zero stop charging the battery Checking battery condition There are three things to do when testing a battery Visual inspection Electrolyte test Operational ...

Page 32: ...done a certain amount of work Fixed load testers are com monly available Variable load testers are not generally found in outdoor power equipment repair shops but are better for testing batteries Capacitance test that checks the condition of the battery plate core regardless of the level of charge Testing the battery 1 Adjustable load testing Adjustable load testing is used if an adjustable load t...

Page 33: ...e bat tery voltage is below what is listed in the chart replace the battery CAUTION It is not recommended to use any fixed load tester on a battery under 200 CCA To do so can boil the water out of the battery and damage the plates in the battery NOTE Because they have a fixed load value they do not give most batteries a reliable and safe load test Most fixed load testers have a load that is more t...

Page 34: ...arge while sitting unused To test for a battery that is leaking voltage 4a Confirm that operator technique is not cre ating a situation that causes a draw As an example if a homeowner habitually turns their equipment off using a safety switch perhaps vacating the seat with the key switch still ON that may leave a relay or fuel shut off solenoid energized 4b Disconnect and charge the battery fully ...

Page 35: ... lamps as a guide to direct the search As an example when diagnosing a no crank condition on a lawn trac tor with a PTO safety switch if the PTO light is lit on the hour meter but the technician has visually verified that the PTO clutch is not engaged the PTO circuit would be a reasonable place to check for problems Check the battery A valid diagnosis of many systems cannot be made without full sy...

Page 36: ...ch connector until the other end of the circuit is reached or the fault is found Voltage Drop Test To review Ohm s law states that it takes voltage to push cur rent through a resistance Kirchhoff s voltage law states that the sum of all the voltage drops equals the source voltage Combining those two laws we see that any restriction in a circuit e g loose connector dam aged wire or corroded termina...

Page 37: ...engine mounting bolts If both of these readings were found on the same tractor a common point in the system would be the primary suspect e g poor connec tion between negative battery cable and frame Applying this principle to the positive side of the system See Figure 7 50 NOTE With the starter engaged this machine exhibited a voltage drop reading of 0 308 volts indicating a poor ground connection...

Page 38: ...op across the two posts of the starter sole noid while cranking the starter motor Testing switches Refer to the Components section of this chap ter that describes the function of the individual switches to be tested Switches can be tested hot by looking for volt age at the appropriate posts This is not defini tive since the source of the voltage is not always confirmed Checking for voltage does no...

Page 39: ...t energize an electro magnet or a solid state equivalent Terminal 3 is a Common connection It may be connected to power or ground depending on the application It is the large spade terminal near the edge of the relay Terminal 4 is the Normally Closed contact When the relay is not energized terminal 4 is connected to terminal 3 When the relay is ener gized this connection breaks An Ohm meter should...

Page 40: ...ty with the NC terminal and continuity with the NO terminal If the results vary from this the relay is bad NOTE To test the relay for burn contacts do a voltage drop test across the relay contacts while the circuit is being used Diodes What is a diode A diode acts like a one way valve allowing current to flow in only one direction See Figure 7 54 Silver band I1 electrons flow from the negative to ...

Page 41: ...the positive lead on the other side of the diode There should be continuity See Figure 7 56 Figure 7 56 Continuity Silver band 7 Switch the leads The meter should indicate no continuity See Figure 7 57 No continuity Silver band Figure 7 57 If the results do not match the above replace the diode 38 ...

Page 42: ...ELECTRICAL SYSTEM SCHEMATICS __ _ _ _ Q F 3_ m LJ dJ LLI 39 ...

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