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JLG 40H 1997 platform controls troubleshooting: PWM or not?

Discussion in 'Forklifts/Telehandlers' started by BrownBear, Jan 29, 2020.

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  1. BrownBear

    BrownBear New Member

    Joined:
    Jan 29, 2020
    Messages:
    2
    Location:
    Wawa, Ontario
    Hi, I just bought a 1997 JLG 40H that operates normally from ground controls, but the engine dies when switched to platform controls. It has spent a lot of time sitting outdoors in extreme weather so I am bracing myself for finding a variety of issues in the controls and boom wiring. The machine is in a remote location so I am trying to make sure I have all the necessary tools when I show up for an extended troubleshooting session.

    It looks like that vintage of 40H uses P-Q Controls joysticks. The thing I am unclear on is whether these emit Pulse Width Modulation (PWM) signals, which would mean if I find an issue with one of those controls I'll want an oscilloscope to examine the output waveform. I have seen conflicting information in the forums about whether this generation of 40H uses PWM in some of the control lines, or some simpler all-on or all-off signaling that I can troubleshoot with just a multimeter. Does someone know for sure?

    Related question: I have found PDFs of the general service and parts manuals but apparently there is technical publication supplement (JLG part number 3120351) with detailed information about adjustment and troubleshooting of the P-Q joysticks. Does anyone know if a digital version of this exists?

    Thanks! - Tim
     
  2. MarshallPowerGen

    MarshallPowerGen Well-Known Member

    Joined:
    Nov 27, 2017
    Messages:
    120
    Occupation:
    Diesel & Generator Mechanic
    Location:
    Coeur d'Alene, Idaho
    I'm no help with the control issue, but found you the supplement in the "Manuals/Supplement Manuals/Joystick Controllers" section
    https://onlineexpress.jlg.com/

    Tried to link it directly to the PDF, but wouldn't work.
     
  3. BrownBear

    BrownBear New Member

    Joined:
    Jan 29, 2020
    Messages:
    2
    Location:
    Wawa, Ontario
    Thanks @MarshallPowerGen for pointing me at the technical supplements. I'm not sure exactly which controllers I have but looks like most of them do emit PWM so guess I'm going shopping for an oscilloscope Screen Shot 2020-01-29 at 4.23.35 PM.png
     
  4. tractormech

    tractormech Well-Known Member

    Joined:
    Feb 19, 2015
    Messages:
    68
    Location:
    florida
    Make sure the red kill button is pulled out or it will die when you switch it over to platform from ground. Also there should be at least one hot wire going up to the platform to fire up the controls.You need to verify voltage there. All of the controllers won't be bad. See if there's a schematic-that's a big help.You may have broken wires in the wiring loom-I've seen them twist and break from extending and retracting the boom over time. Also a serial number would be helpful.