ISOLATE MALFUNCTIONS TO COMPONENT LEVEL IN
THE DENTAL CHAIR AND STOOL
In order to efficiently maintain the dental chair, model JSR, you need to
understand how it operates. This lesson covers how the circuit works. It also covers
how to use a troubleshooting chart to isolate certain malfunctions. The malfunctions
chosen are examples of the methods to use to isolate common malfunctions.
THEORY OF OPERATION
Refer to figure 2-1.
a. Raising the Chair. To raise the chair you use the foot switch. This applies
(1) When you use the foot switch, 125 volts alternating current (vac) is
applied from the incoming line through the black wire to the common of the mode
switch. With the AUTO/MANUAL mode switch in the manual position, continuity is
maintained to a tie point in the junction box, then out the junction box along the lower
black wire to the common of the foot switch. With the foot switch in the up position,
potential is applied through the switch, along the red wire, through the limit switch to the
motor. The other side of the motor is tied to the incoming neutral line.
(2) You raise the chair by the use of a scissors jack assembly. As the motor
runs, worm gears turn a sprocket. The sprocket connects to a chain which turns a
screw shaft running through the center of the scissors jack. The jack is mounted to the
base plate and the seat base. Clockwise movement of the shaft raises the chair.
Counterclockwise movement lowers the chair.
b. Lowering the Chair. You lower the chair through much of the same circuitry
as raising. Power is applied to the AUTO/MANUAL mode switch (still in manual) to the
tie point in the junction. From there it flows along the lower black wire to the foot switch.
With the foot switch closed to the "lower" position, power is applied through the switch,
out of the blue wire to the manual "lower" limit switch. It then goes to the motor and out
the neutral white wire.