Charge Pressure is used, among other things, to release the brakes.
The charge pressure should be 360psi. This pressure is directed to the brakes through the brake valve.
If the charge pressure is too low or if the voltage at the brake valve is too low or not there, then your symptom will be evident.
There is a pressure test port on the drive pump that will let you connect a pressure gauge to (0 to 5000psi).
Connect the gauge and start the engine. 360psi should be present. (The 0 to 5000psi gauge is in case the joystick is pushed while the gauge is hooked up. The pressure could soar to 3500 immediately).
If the pressure is less than 250, brake issues can develop.
If this pressure is ok then the next point of concern in the circuit is the brake valve.
We need to verify there is at least 10volts at the brake valve when the drive joystick is stroked. 12volts is better but the valve should open at 10 or so.
As Willie said, there should be 12 volts at terminal 1 of the drive joystick when it is stroked either direction. If there is, the next point to check will be terminal 32 of the terminal board in the upper control box. The next point to check there is at terminal 32 in the lower control box, and finally at the valve coil itself.
If there is no voltage at terminal 1 of the drive joystick when stroked, check the angled micro-switch on the joystick. This is the brake release switch.
If the voltage is ok, the solenoid coil will need to be checked out.
With engine off, remove the brake valve cartridge from its block. Install the coil to the cartridge, apply 12 volts to the coil and verify the cartridge spool is moving in the cartridge.
This will probably be as far as you need to go before you find the problem.
If not, it will get a bit more of a challange.
This machine was built before the usage of divider-combiner valves in the circuit.
They used flow regulator and flow control valves in the drive manifold.
What appears to be brakes locking up can actually be flow that is blocked from a motor or flow added to both sides of a motor at the same time. This happens when the valves in the manifold stick.
The drive manifold is the lowest hydraulic assembly in the system so it is where all the water and debris settle.
Very prone to causing problems of this nature on older machines or machines not well maintained.
We will cross that bridge when we come to it
