JLG 40HA wont go down

Let a friend use my lift now they have the tower boom stuck all the way up. When you hit the down switch the motor loads up and pushes a little oil out of the top of the cylinder. It acts like it is locked not trading the oil back out of the safety valves.
Any ideas would be greatly appreciated
Thanks

I've been through this......unfortunately. There is an extra button/switch below the ground control panel that's supposed to allow you to bring that section back down. It didn't work. Btw, it happened to us when we lent our machine out to someone. No idea what they did to it. When I got the call it was stuck inside a building with the tower boom all the way up. We messed with it for 1/2 a day before we got a crane in there, supported the boom, removed the holding valves on both boom sections and blew oil all over hell as the crane let everything settle back into place. After that we got the machine back to the shop, replaced the holding valves and never had it happen again. Messy, messy, messy, and more messy. Hope you find a better solution than I did.

Thanks I was thinking of the same thing
Hoping to avoid the mess

we were trying to back-off the adjustments on the holding valves so they would release, but it's like the holding valves on the two boom cylinders are in series and the main boom has to release but still pressure a port on the tower boom valve for it to release. We gave up made messy. Be careful. You are right in the line of fire when you're messing around. I don't know what I would have done if there wasn't a crane and an operator close at hand.

When dealing with boom trucks I have had situations where if you topped out the boom cylinder at speed it caused a pressure spike on the piston side, and you could not develop enough pressure on the rod end to pop the lock valve open.

I have seen some of these load lock valves where you have to turn the screw IN to lower the pressure setting. Don't know why but it's worth a try. Don't put yourself in the crush zone!

ok finally got it in my shop. Been messing with it for two days. What I have found is if I unhook the tower lift up wire from the solenoid when shut off nothing happens. If I start the machine and try to lift the tower lift the machine stalls like it does when I am trying to lower the tower lift.
I would think that it should not do anything because the up solenoid is unhooked.
I have took all the pressure relief valves out of the cylinder and removed the hydraulic lines and have relieved the pressure with nothing changing
Any thoughts
Thanks

Can anyone tell me where or what these load locking valves look like or are located? Our boom is stuck in the up position. There’s just to many hoses to follow and I’ve given myself a headache trying to follow the diagram

right underneath the ground controls there should be three handles, there is a description on how to use them in what order on the door try that first