[jclark003]

I'm assuming the 40 has hydraulically actuated tables. If so Guessing It could be either the valve (attached to the hydraulic pump), the lovejoy connector on the jack screw shaft or something jamming the mechanism. i would start by trying to locate the humming noise. If it's coming from hydraulic power unit I would be looking at valve. You can try swapping up and down valves to see if the problem reverses. If coming from under table then it's somewhere in the jack screw or lovejoy that connects the shaft to motor. If you can lift table while someone is hitting up button you may get it in the up position to get access to mechanism. If not there may be an inspection hatch under the insulation. Good luck.