JLG 40h boom goes up but come down and other issues.

[stephen4785]

Iv been thrust into a job on this 40h. It came in being unable to steer, boom up/down, any switch in the basket working. I found one prv bleeding by and fixed it. I supplied 12v to the dump valve and now had enough pressure to see that a hose had a pinhole and sprayed hyd fluid through the wiring harness and melted/cut it. I pulled the harness out and patched it. Re-installed everything and now I have steering, some controls in the basket. The main problem I have right now is that the boom goes up but not down. When I hit the down switch and hold it I can hear the motor bog down and the boom goes down a couple inches then stops. I have 0 psi at the boom control bank of solenoids. If I supply 12v to the dump valve I get 5000psi but the boom still does not go down. The boom is all of the way in. Everything else on the ground control works fine. The basket however has a few things that work. The speed control, rabbit/turtle, boom down, and boom right dont respond(im not sure it the speed control is related).
Thanks for any help.

 

[stephen4785]

to clarify-the boom control for engine speed, pump volume, and creep dont work at all.

 

[Moonlite]

I would look at wiring harness again. As a place to start. Then start checking voltages coming into platform and leaving platform. I asume that ground control functions are working?

 

[stephen4785]

everything on the ground control works fine except for the boom down. One thing I have noticed is that the voltage on the swing function(ground control) is only 3v. If I jump 12v to it the swing goes around a lot faster so Im assuming thats how the rabbit/turtle function works but Im unsure.

 

[willie59]

Engine throttle, wheel speed, and pump volume only operate when driving the machine. Creep works with the proportional functions at the platform only, that is if the controllers are operating and adjusted properly. And you can't test the output of the proportional controllers at the platform by simply using a volt meter because the output is pulse width modulation, one would have to check their output with an oscillometer, yeah, everybody has one of them in their back pocket. But the outputs to the control valves from the ground controls is 12V from toggle switches, you should be able to check/test the wiring going to the boom down valve with a volt meter and narrow down the problem. The 40H came with either PQ or OEM controllers, and were fitted with either Racine or Vickers proportion control valve.

 

[stephen4785]

Engine throttle, wheel speed, and pump volume only operate when driving the machine. Creep works with the proportional functions at the platform only, that is if the controllers are operating and adjusted properly. And you can't test the output of the proportional controllers at the platform by simply using a volt meter because the output is pulse width modulation, one would have to check their output with an oscillometer, yeah, everybody has one of them in their back pocket. But the outputs to the control valves from the ground controls is 12V from toggle switches, you should be able to check/test the wiring going to the boom down valve with a volt meter and narrow down the problem. The 40H came with either PQ or OEM controllers, and were fitted with either Racine or Vickers proportion control valve.

Do you know what I should check as far as getting the boom to go down? When I hold the switch down I can hear the motor change pitch and Im getting voltage across the switch itself. Iv checked voltage at the down solenoid and Iv got voltage there. I hooked a pressure gauge to the back of the solenoid block and it doesnt move off of 0. Is there an interlock that I need to look at?

 

[willie59]

Have you downloaded the manuals for that machine to have the diagrams you need?