I recently bought a 690d with 7800 hrs at auction. All functions on machine seemed to operate fine. When truck driver was loading machine hydraulics functions all stopped as if pilot valve was disengage. They pulled pinion shafts out and finished loading. I'm trying to trouble shoot. Hydralic oil leval is in normal range. Pilot valve lever linkage is free and operational. I tested pilot pressure, 650psi at half throttle. I then tested pilot pressure at main valve body for up and down stick function, about 400psi. Main pump doesn't seem to build any pressure. I do no that main pump and pilot pump have been replaced at some point. I'm currently waiting on the Deere repair and test manuals. Is there any other things to check that can be easily overlooked? Thanks