Haven't had a chance to look at the schematics, but lift the boom and walk away, and it doesn't drift. Lift the machine and walk away, and it doesn't drift. I cannot duplicate the complaints. Operator 1 says there is a slight drop when requesting boom up. Operator 2 says when lowering and stopping, say 6 inches above the ground, the boom taps the ground when letting go of the control. Again, I cannot duplicate either concern. Any thoughts out there on where to start?
Spool valve.
Debris? Seal? Pilot cap? Broken spring? Common issue?
Could be any of the above, but could be like at one place I worked. Decided in my head it was two disgruntled employees, Dealer mechanic could find nothing wrong. Both employees quit and never even heard of the problem again in 1.5 years. Just saying, you never know. Simon C
Before trying to fix an issue, you have to verify something is actually wrong. I have noticed fixing machines for 40 years, some operators are used to things a certain way and will never be happy until they change machines or get a new machine. I once had an operator try and convince me there was a cold virus in a GMC TopKick and refused to drive it until I had taken the whole dash apart and clean all vents and ducting and coils, with Lysol. He was nuts but it made him happy. It did take a bit to free up some time but hey. If you can’t find a place to start, you’re not gonna have good success.
you might have a pilot pressure or joystick poppet issue. the boom circuit has anti drift spools on top of the control valve and if the pilot pressure does not move the spool fast enough there will be a drop in the boom before it comes back up, normally you see this when the operator is barely moving the stick to boom up. could be the same issue for boom down. the pilot pressure should be set to 750 with hot oil at high idle and make sure it doesn't drop below 600 at low idle. the pressure at the spool should be around 450psi.
Regeneration check valve in the main control valve. Fixed the same problems in a Hitachi and Case. Likely some trash/debris got in there. In asian excavators the schematic seems to accurately show what is happening, but once you the valve apart, it is a mystery where exactly any poppet/check is and does. Even in the factory schooling I took, the instructors could not point out what was what. I fixed both by completely disassembling and cleaning (a few bad words/threats) and it worked. hope this helps