Problem solved! I can't thank you enough sonavor! With your invaluable pictures as a guide I disassembled the tracking force adjustment knob and adjusted the smal dented gear that has the spring. Now the adjustment knob is extremely accurate no matter what the setting is. However the fact that the knob was tightly screwed in place leads me to the conclusion that the problem was the spring itself. After forty years it seems that these little springs lose tension and have to be readjusted. This is the only way that the tracking force adjustment knob can become accurate again. Maybe this procedure should be part of regular maintenance of all 400x turntables.
After your pictures maybe we can expect a new video by Beolover entitled "Calibrating the tracking force adjustment gears"....
Milton
