Looking for advice on a 98 JLG 40e. She has very little power in forward and a little bit more in reverse. All other functions are normal working order. I tried to load it in cold weather on a trailer and since then has had this issue. Could it be the style reversing contactor? Thanks for any help.
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98 JLG 40e Problem
- Thread starter schase
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VoodooMojo
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chances are no that the contactor will be an issue. The Forward-Reverse Contactor only sets up the polarity of the drive motor Field Windings.
Seeing you have forward and reverse it would appear that the contactor is fine.
A couple things you will want to check are the Elevation Limit Switches at the boom pivots and the Creep (snail) Switch at the Function Speed Control Knob at the upper control box.
Typically the problem you describe having was found at the Creep Switch at the Function Speed Control Knob at the upper control box.
There is a detent when the Speed Knob is turned fully counter-clockwise.
When the knob is rotated past this detent position there should be a click.
This is the sound of a switch opening to put the drive speed into Creep Mode.
This switch is in line with the Elevation Switches (upper and lower).
When this model was introduced, 1996, the Creep Switch (snail) was not on the machine.
The issue at the time was when truck drivers were unloading the machine on an incline, the unit would freewheel down the grade a bit before the Plug Braking (dynamic) would kick in. This was un-nerving to say the least! Many resourceful drivers found that if they elevated the tower (lower) boom enough to get it off the limit switch, the machine would come down the grade nice and slowly. JLG then went ahead and installed the Creep Switch to achieve the same results and to facilitate easier unloading.
The problem with the switch is it is not very robust and can be broken easily.
Just turning it counter-clockwise a bit too roughly will cause it to continue rotating around and around. Usually the switch would just break.
When this happens, the unit is put into low speed.
The easiest and most effective method of diagnosing this is by putting a Voltmeter at pin 4 of the 17 pin plug that plugs into the DC Motor Controller. This should be an Orange wire.
This is the box located on the back wall between the two drive motors in the motor compartment at the rear of the chassis.
It will have either SEVCON Controller or JLG Motor Controller written on it.
Place the voltmeter Negative lead on the B- terminal of the Motor Controller and back-probe the voltmeter Positive lead into the terminal # 4 of the 17 pin plug on the motor controller. When the machine is in the Stowed Position, there should be 48 volts present at terminal 4. Be sure the machine is set to operate from the upper controls, power on, foot on the foot pedal and the drive joystick stroked in either forward or reverse.
Be Careful for yourself and others. Jacking up the rear of the unit so the wheels are off the ground is helpful also.
If the 48 volts is not there the motor controller will think the booms are elevated and put the unit into creep drive mode.
There are a couple other plugs on the machine where this 48 volt signal travels through.
Not far (usually resting under or near the left rear drive motor) from the 17 pin plug is a 15 pin plug. Check this plug for damage or corrosion.
Also, along side the Main (upper) Boom is a 31 pin plug. It is under a cover on the side of the upper boom.
If the problem is not the Creep Switch, it may be in one of the Elevation Switches. Same test (48 volts at pin 4 when stowed) will verify proper operation.
There is also another possibility (not being a problem with the creep or limit switches) that the proportional signal from the Drive Joystick is being compromised.
This is also easily checked by back-probing pin # 14 at the 17 pin plug at the motor controller.
In neutral, the signal at pin 14 should be near 5.0 volts and proportionally travel down towards 0 volts as the joystick is moved towards full stroke forward or reverse.
This voltage should change smoothly as the joystick is moved.
Let us know if you need assistance with this.
Good luck!
Seeing you have forward and reverse it would appear that the contactor is fine.
A couple things you will want to check are the Elevation Limit Switches at the boom pivots and the Creep (snail) Switch at the Function Speed Control Knob at the upper control box.
Typically the problem you describe having was found at the Creep Switch at the Function Speed Control Knob at the upper control box.
There is a detent when the Speed Knob is turned fully counter-clockwise.
When the knob is rotated past this detent position there should be a click.
This is the sound of a switch opening to put the drive speed into Creep Mode.
This switch is in line with the Elevation Switches (upper and lower).
When this model was introduced, 1996, the Creep Switch (snail) was not on the machine.
The issue at the time was when truck drivers were unloading the machine on an incline, the unit would freewheel down the grade a bit before the Plug Braking (dynamic) would kick in. This was un-nerving to say the least! Many resourceful drivers found that if they elevated the tower (lower) boom enough to get it off the limit switch, the machine would come down the grade nice and slowly. JLG then went ahead and installed the Creep Switch to achieve the same results and to facilitate easier unloading.
The problem with the switch is it is not very robust and can be broken easily.
Just turning it counter-clockwise a bit too roughly will cause it to continue rotating around and around. Usually the switch would just break.
When this happens, the unit is put into low speed.
The easiest and most effective method of diagnosing this is by putting a Voltmeter at pin 4 of the 17 pin plug that plugs into the DC Motor Controller. This should be an Orange wire.
This is the box located on the back wall between the two drive motors in the motor compartment at the rear of the chassis.
It will have either SEVCON Controller or JLG Motor Controller written on it.
Place the voltmeter Negative lead on the B- terminal of the Motor Controller and back-probe the voltmeter Positive lead into the terminal # 4 of the 17 pin plug on the motor controller. When the machine is in the Stowed Position, there should be 48 volts present at terminal 4. Be sure the machine is set to operate from the upper controls, power on, foot on the foot pedal and the drive joystick stroked in either forward or reverse.
Be Careful for yourself and others. Jacking up the rear of the unit so the wheels are off the ground is helpful also.
If the 48 volts is not there the motor controller will think the booms are elevated and put the unit into creep drive mode.
There are a couple other plugs on the machine where this 48 volt signal travels through.
Not far (usually resting under or near the left rear drive motor) from the 17 pin plug is a 15 pin plug. Check this plug for damage or corrosion.
Also, along side the Main (upper) Boom is a 31 pin plug. It is under a cover on the side of the upper boom.
If the problem is not the Creep Switch, it may be in one of the Elevation Switches. Same test (48 volts at pin 4 when stowed) will verify proper operation.
There is also another possibility (not being a problem with the creep or limit switches) that the proportional signal from the Drive Joystick is being compromised.
This is also easily checked by back-probing pin # 14 at the 17 pin plug at the motor controller.
In neutral, the signal at pin 14 should be near 5.0 volts and proportionally travel down towards 0 volts as the joystick is moved towards full stroke forward or reverse.
This voltage should change smoothly as the joystick is moved.
Let us know if you need assistance with this.
Good luck!
Last edited:
VoodooMojo
Senior Member
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The previous post is with the assumption that the batteries are up to snuff.
The first test I would perform is to read the battery voltage at Terminals B+ and B- at the Motor Controller while under load (attempting to drive the machine).
If the voltage drops significally, then batteries and/or connections are suspect.
I always preach to "never overlook the obvious"
I guess I did!
The first test I would perform is to read the battery voltage at Terminals B+ and B- at the Motor Controller while under load (attempting to drive the machine).
If the voltage drops significally, then batteries and/or connections are suspect.
I always preach to "never overlook the obvious"
I guess I did!
willie59
Administrator
You beat me to it Voodoo, I have to beat myself in the head to always remind myself to "check the batteries first knot head", been bit by that more than once. :Banghead 
VoodooMojo
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I hear what you are saying Willie!
I know I tick off more than a few people a day when they call for troubleshooting advice and I ask them about the basics (voltage, current, hyd pressure or flow).
They wonder if I think they are stupid.
But there have been many, many times when I don't ask the simple questions that, as you say, I get bit by it after a great deal of time has elapsed troubleshooting.
I know I tick off more than a few people a day when they call for troubleshooting advice and I ask them about the basics (voltage, current, hyd pressure or flow).
They wonder if I think they are stupid.
But there have been many, many times when I don't ask the simple questions that, as you say, I get bit by it after a great deal of time has elapsed troubleshooting.
Last edited:
willie59
Administrator
Absolutely. And so many think you're crazy because "all my boom functions are working fine". But the don't realize that the drive is controlled by a Sevocon or some other motor controller, battery voltage gets just a little low, not anywhere near dead, and that motor controller starts knocking out drive. :yup
First off, thanks for the advice! I will be looking into these things in the next couple of days. I do know the batteries are only two years old and I always keep them charged and never let the water go down with them so I am thinking/hoping its not that. The creep switch works fine with all functions of the boom so I am assuming (we all know what that does haha) that this also isn't the issue. Here's what I do know, the day that it started as I said was very cold as I live in Maine, and the temp was probably around 25 degrees. It had an increasingly hard time going up the ramps onto my trailer and has not been the same since then. Like I was saying though all other functions act normally as before so it would seem it's something that got burned/arced and is now not allowing full voltage to the drive motors. At least that is what it seems to me and I am in no way an electrical expert. I will do some investigation into those possibilities and see what I can find. Thanks again for all the help!
Oh, thought of one more thing, the forward drive seems to have less power to drive it than it does in reverse (also that is the direction it was traveling onto the trailer that created the issue). Also, it will "kick out" at points and you can hear a lot of "clicking" when it does this. If you let off the joystick and try again that is how to get beyond it so it will move at all.
willie59
Administrator
Have you checked if you have fault codes at the MOS90 motor controller? Sometimes codes will remain flashing after a fault occurs in drive functions. Other times, you depress foot switch, operate drive, and when fault occurs, hold foot switch and controller in position when fault occurred and have helper check MOS90 fault codes.
willie59
Administrator
Should be an LED light on motor controller. Solid on LED indicates functions normal. No LED on indicates internal failure. Flashing LED indicates fault codes. It will flash a code, short pause, then flash code again.
VoodooMojo
Senior Member
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- Jan 18, 2012
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- 344
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the condition you describe sounds a bit like the fwd/rev contactors clicking on and off.
This is reflective of the tach generator being defective or in need of a cleaning.
The tach generator is the appendage attached on the left drive motor.
It is an analog voltage device not unlike the generators that used to rub against a bicycle tire to generate a voltage to light a headlamp/taillight.
It is very easy to test.
It puts out approximately 20 volts per 1000 RPM (if memory serves correctly).
Spinning the shaft in one direction will produce a positive voltage and spinning it the other direction will produce a negative voltage.
To test, simply remove the generator from the drive motor, place the shaft of the generator into a reversible, variable speed drill.
Note the color wires that were connected to the generator and remember the post numbers they are on. If the wires are interchanged, the motor controller will be confused and think the machine is running backwards.
Connect the positive and negative leads of an analog-type voltmeter to the two terminals the wires came off of. A digital meter will work but the needle of an analog meter will show a nice smooth sweep across the meter face and better reflect any bad spots where the generator is putting out a sporadic signal.
While observing the voltmeter, slowly increase the speed of the drill and check for a smooth increase of the voltage output of the generator. Also note the polarity of the voltage.
Slowly decrease the speed of the drill and note the smoothness of the voltmeter as the generator slows.
Reverse the drill direction and repeat the test. Be sure the polarity is opposite that of when the generator was spinning in the other direction.
It is very important that the voltage from the tach generator has a smooth increase and decrease movement and is reflective of the speed and direction of the generator shaft.
The tach generator is used to tell the motor controller how fast the machine is traveling and also the direction it is traveling in.
When you are scooting across the floor in forward, for instance, and the joystick is released back to neutral, the tach generator is telling the motor controller what direction the machine is traveling (by the polarity) and how fast the machine is traveling (by the potential). The motor controller at this time will disconnect the forward contactor and activate the reverse contactor and use dynamic braking (plug) to slow the machine down to a stop. When the machine reaches a full stop and the motor controller senses no movement of the drive motors, it will then release the brake contactor, letting the parking brake apply.
If the motor controller is sensing erratic signals from the tach generator while driving, it starts flipping back and forth between the forward and reverse contactors trying to regulate the speed and direction of the machine. This is the clicking you are hearing.
The signal from the tach generator is also used to regulate the high drive speed of the unit.
The generator can be cleaned to reduce this erratic signal.
Being very careful, remove the wires attached to the small terminals of the tach generator. Real Careful.
There is the nut, a small washer, the wire end, and than another hex-head stud (that the wire was attached to) that has a spring and brush attached.
Carefully remove the two brushes from the generator and set aside for re-use.
Remove the other small screws holding the end plate of the generater on. When the cover is removed, a metal disc that the brushes rub on will be visible.
Clean this disc with a solvent such as brake-clean.
Reassemble and test again.
Be very careful re-attaching the wires to the generator studs. The threaded part of the stud is very easy to break or crossthread.
The tach generator is an analog component and the motor controller is digital.
There is an interface board between the two that converts analog to digital. This is the small board located to the left of the motor controller. Check the connection and make sure they are clean and secure.
If by some chance this unit has the old photocell type speed sensor, it can be adjusted and cleaned also.
This is reflective of the tach generator being defective or in need of a cleaning.
The tach generator is the appendage attached on the left drive motor.
It is an analog voltage device not unlike the generators that used to rub against a bicycle tire to generate a voltage to light a headlamp/taillight.
It is very easy to test.
It puts out approximately 20 volts per 1000 RPM (if memory serves correctly).
Spinning the shaft in one direction will produce a positive voltage and spinning it the other direction will produce a negative voltage.
To test, simply remove the generator from the drive motor, place the shaft of the generator into a reversible, variable speed drill.
Note the color wires that were connected to the generator and remember the post numbers they are on. If the wires are interchanged, the motor controller will be confused and think the machine is running backwards.
Connect the positive and negative leads of an analog-type voltmeter to the two terminals the wires came off of. A digital meter will work but the needle of an analog meter will show a nice smooth sweep across the meter face and better reflect any bad spots where the generator is putting out a sporadic signal.
While observing the voltmeter, slowly increase the speed of the drill and check for a smooth increase of the voltage output of the generator. Also note the polarity of the voltage.
Slowly decrease the speed of the drill and note the smoothness of the voltmeter as the generator slows.
Reverse the drill direction and repeat the test. Be sure the polarity is opposite that of when the generator was spinning in the other direction.
It is very important that the voltage from the tach generator has a smooth increase and decrease movement and is reflective of the speed and direction of the generator shaft.
The tach generator is used to tell the motor controller how fast the machine is traveling and also the direction it is traveling in.
When you are scooting across the floor in forward, for instance, and the joystick is released back to neutral, the tach generator is telling the motor controller what direction the machine is traveling (by the polarity) and how fast the machine is traveling (by the potential). The motor controller at this time will disconnect the forward contactor and activate the reverse contactor and use dynamic braking (plug) to slow the machine down to a stop. When the machine reaches a full stop and the motor controller senses no movement of the drive motors, it will then release the brake contactor, letting the parking brake apply.
If the motor controller is sensing erratic signals from the tach generator while driving, it starts flipping back and forth between the forward and reverse contactors trying to regulate the speed and direction of the machine. This is the clicking you are hearing.
The signal from the tach generator is also used to regulate the high drive speed of the unit.
The generator can be cleaned to reduce this erratic signal.
Being very careful, remove the wires attached to the small terminals of the tach generator. Real Careful.
There is the nut, a small washer, the wire end, and than another hex-head stud (that the wire was attached to) that has a spring and brush attached.
Carefully remove the two brushes from the generator and set aside for re-use.
Remove the other small screws holding the end plate of the generater on. When the cover is removed, a metal disc that the brushes rub on will be visible.
Clean this disc with a solvent such as brake-clean.
Reassemble and test again.
Be very careful re-attaching the wires to the generator studs. The threaded part of the stud is very easy to break or crossthread.
The tach generator is an analog component and the motor controller is digital.
There is an interface board between the two that converts analog to digital. This is the small board located to the left of the motor controller. Check the connection and make sure they are clean and secure.
If by some chance this unit has the old photocell type speed sensor, it can be adjusted and cleaned also.
Back again. We raised the lift in the air so that there is no load on the drive tires and when the lift drives the motor on the right turns at 1/3 the speed of the other motor. This seems odd since it appears that the motors are wired in parallel and should recieve the same voltage from the motor controller. Any ideas?
VoodooMojo
Senior Member
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- Jan 18, 2012
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- 344
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- Baltimore, East Coast USA
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- Sr Technical Service Representative
The motors are wired in series. If they were wired in parallel, it would be all but impossibe to make a turn with something as unsophisticated as the Sevcon controller on it.
When the machine is jacked up off the floor, the motor/brake/hub assembly with the least resistance will turn the fastest.
If you can apply a bit of restriction to the motor that is spinning the fastest, the slow motor should speed up. If not, then this is an indication of a motor issue.
When the machine is jacked up off the floor, the motor/brake/hub assembly with the least resistance will turn the fastest.
If you can apply a bit of restriction to the motor that is spinning the fastest, the slow motor should speed up. If not, then this is an indication of a motor issue.
VoodooMojo
Senior Member
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- Baltimore, East Coast USA
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I normally just apply pressure by lifting up against one of the spinning wheels with a length of lumber or metal bar.
Be careful to not insert the bar in the direction that it could be chucked back at you. That can be painful.
Be careful to not insert the bar in the direction that it could be chucked back at you. That can be painful.
willie59
Administrator
For sure, that's one of those rare moments in life when one asks oneself..."dang dumb ass...why'd you do that?"