JLG 40E stuck in slow motion mode

Do you now have 48v at pin 7 yellow on the sevcon?

If so check pin 13 white/violet with a boom function engaged and vary the boom speed knob.

That will tell us if the sevcon is seeing the boom speed command.

Yes, I am getting 47V at pin 7 yellow. When I engage a boom function at pin 13 with the speed control knob at the detent I get 2 volts. As I turn it clockwise (speed up control knob) the voltage drops from 2 volts slowly down to 0 volts when the speed knob is all the way fast. If I stop the speed knob half way between slow and fast it will remain at around 1 volt give or take.

We're making progress. If the unit was working correctly the boom functions would go into creep mode when above elevation and tilted.

Does the pump speed knob have any affect on the boom speed?

I'm not sure what the speed signal should be at pin 13 other than it comes from pin 2, up through the pot, then back down to pin 13. With the pot fully clockwise the reading should be the same at 2 and 13.

I had a cheat sheet from when the 30E first came out but that's long gone.

What is the voltage across the battery pack?

Across the battery pack we are getting 47.5 volts
Yes the pump speed knob works but it is still in a lethargic mode. When turned to the slowest setting the booms barely move if at all. When the speed knob is turned to the fast setting the booms lift but very slowly as if it were in a creep mode but as soon as you press the steering function either left or right, the booms kick into normal high speed operation.

With the platform foot switch pressed and no other functions activated, we get 2 volts at pin 13. When you turn the speed knob this volts progressively lowers down to zero. It progressively increases back to 2 volts when turned the opposite way.

I will have to try pin 2 tomorrow am as a massive thunderstorm is approching.
We truly appreciate the effort to fix this and we will compensate you once its running. Thanks again

Can you plug it in?

47.5 volts is nearly dead. Fully charged resting voltage should be 50.4 and will approach 60 as the charger is finishing up.

Haven't charged in a week but will place it on charge. Replaced 4 batteries and prior to the replacement was getting 38-41 volts. It actually was working fine even back then. I've lifted the steering wheels to get a full turn left to right or right to left and the unit still will 'kick" into normal operation at the 47.5 volt when the steering wheels turned and a boom function in operation.
Will charge over the weekend and retest the above procedures again.

When you activate steer a contactor puts full power to the pump motor bypassing the sevcon.

When operating normally the sevcon meters the current going to the motor.

Some of these had low voltage protection built into them.

You may want to check the individual batteries and charge some individually or in pairs if they are out of balance, also check the pack voltage under load.

Charged over the last few days. Problem still acts the same.
Battery 1. 6.56 v
2. 6.31
3. 6.78
4 . 6.27
5. 6.96
6. 6.81
7. 6.70
8. 6.54

Will attempt the procedures above again.

Rick,
Fully charged and tried all above procedures. Still no go.

Any idea how to get the drive motors to function? Looks like the booms will not speed up and may take to repair facility. Just cant figure this out......
Can we try and tackle the drive motors. Moving the joystick I get nothing. Neither forward or reverse...
So frustrated!!!

could the proportional relief valve cause the lift to operate in slow motion mode? When activating the steer function it "kicks" into normal operation. Thinking outloud to get this thing fixed to cut hurricane trees down on the property.

I purchased a 1996 JLG 40E a few months ago. All functions seemed to work fine, all lift functions, rotation, etc. but the drive system was very slow and lethargic no matter how the potentiometer was set. When I checked the batteries that the previous owner had in place, they were a hodgepodge of different sizes with only 3 of the correct batteries, so I purchased a complete set of new, correct batteries. The drive was still lethargic and now the lower boom tries to lift but does not rise more than an inch no matter what the potentiometer is set at. Frustrated I left it alone for a week, when I went back to it now the lower boom works fine for a while, then while I was trying to use the unit, now the lower boom won't lift anymore and has not since. Yes, the drive is still lethargic and I actually had to tow the unit with my tractor at one point to get it to move. I tested the motor controller and the voltage from the #4 pin and B- is over 50 volts, both static and under drive. I jacked up the drive wheels and they both move in both forward and reverse, but had no real power. Are these two issues, failure of the lower boom to lift and lethargic drive connected? All other functions work fine. Can anyone help me figure this one out. Thanks in advance!

ARToolDoc said:

I purchased a 1996 JLG 40E a few months ago. All functions seemed to work fine, all lift functions, rotation, etc. but the drive system was very slow and lethargic no matter how the potentiometer was set. When I checked the batteries that the previous owner had in place, they were a hodgepodge of different sizes with only 3 of the correct batteries, so I purchased a complete set of new, correct batteries. The drive was still lethargic and now the lower boom tries to lift but does not rise more than an inch no matter what the potentiometer is set at. Frustrated I left it alone for a week, when I went back to it now the lower boom works fine for a while, then while I was trying to use the unit, now the lower boom won't lift anymore and has not since. Yes, the drive is still lethargic and I actually had to tow the unit with my tractor at one point to get it to move. I tested the motor controller and the voltage from the #4 pin and B- is over 50 volts, both static and under drive. I jacked up the drive wheels and they both move in both forward and reverse, but had no real power. Are these two issues, failure of the lower boom to lift and lethargic drive connected? All other functions work fine. Can anyone help me figure this one out. Thanks in advance!

Click to expand...

hey Art,

I still have the same issues with mine. I have all new batteries, drive motors were rebuilt and still is slow motion. I may replace the motor controller but thats $$$$ and I can't figure anything else as I've checked all wiring and fuses and such.

rookieatbest said:

hey Art,

I still have the same issues with mine. I have all new batteries, drive motors were rebuilt and still is slow motion. I may replace the motor controller but thats $$$$ and I can't figure anything else as I've checked all wiring and fuses and such.

Click to expand...

Really frustrating

I keep reading about how the speed potentiometer gets forced beyond the normal stop, causing creep mode to stick, but cant find how to really fix or bypass it.
The lower boom has worked sporadically, but now tries to lift, but wont.

that would make sense. Since we have the same issue I'm sure we can try a couple of things. I'm heading out of town for a week but will try and troubleshoot again. My steer functions work fine as thats on a separate circuit. My drive and boom functions are very slow...
If I press a steer on the joystick and try to elevate a boom, it "kicks" into normal operational mode. Does yours do that?

rookieatbest said:

that would make sense. Since we have the same issue I'm sure we can try a couple of things. I'm heading out of town for a week but will try and troubleshoot again. My steer functions work fine as thats on a separate circuit. My drive and boom functions are very slow...
If I press a steer on the joystick and try to elevate a boom, it "kicks" into normal operational mode. Does yours do that?

Click to expand...

Upper Boom lift, extend, tilt, rotate all work as they should. The lower boom lift tries, pump starts, boom moves a tiny bit, but the pump continues with no more action. When you reverse the lower boom to move down it jumps down the tiny bit it moved. I have not tried flipping the steering rocker while trying to elevate the lower boom, but I will try that tomorrow. Have you replaced the speed potentiometer and if so did it make any difference?

Yes I replace the speed pot, and replace the joystick as well as mine unit will not drive either. Also the tilt sensor was replaced and both limit switches on the booms seem to check out fine. My booms will lift about a couple of inches and then you can hear the pump still running but it doesn't budge. My speed pot would go past the indent and I thought that was the issue, but the new one didn't fix my problems. I'll keep trying after my trip.

Sounds like we have identical problems, except I have not replaced anything but the batteries at this point. How did you test the limit switches and where are they? I thought about replacing the joystick, but when I jacked up the drive wheels, the joystick worked fine, but didn't seem to have much power and that seems crazy as electric motors have a great deal of torque normally. My unit is a 1996 and from what I could find, they didn't come with the "Creep Mode", but it certainly acts likes that is what it is stuck in. I'm going to check out the motor controller and see if I can tell if that has been changed out, and if so the replacement might be newer with the "Creep Mode". One thing that is driving me crazy is the fact that the lower boom worked fine with the crappy batteries that were in the unit when I purchased it, but now, with new batteries it has worked sporadically, but now just tries to lift. I kept trying it and the lower hydraulic cylinder blew a seal, so I had it rebuilt, no leak now, but still won't lift. I actually wonder if the cylinder was bad before, but all of the lift pressure went to that cylinder and over pressured it, but I don't know. There is only one hydraulic pump, that switches from one function to another. The upper lift works great, the boom extension works fine, drive works on level ground with minimal power, but will not climb any grade at all and the lower boom will not work now. I don't understand!!

search this in this forum.. its my previous troubleshooting

JLG 40E boom synchronizing