ISOLATE MALFUNCTIONS TO COMPONENT LEVEL IN
THE DENTAL CHAIR
In order to efficiently maintain the dental chair, model JSA-R, you need to
understand how it operates. This lesson covers how both the manual and automatic
mode circuits work. 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. This lesson covers the following malfunctions: the chair will not
operate, the manual control switch fails to raise or lower the chair, and the automatic
control fails to operate when the manual controls are operating.
THEORY OF OPERATION
a. Manual Mode Circuit Description. Refer to figures 2-1 and 2-2.
(1) Raising the chair. To raise the chair you use the bottom switch on the
assistant's side of the chair or the foot switch. This applies power.
(a) When you use the foot switch, 125vac (volts alternating current) is
applied from the incoming line through the black wire to the common of the mode
switch. With the 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.
(b) When you use the push button switch, power is applied from the
incoming line, through the mode switch. It travels to the tie point in the junction box,
through the middle black wire to the common of the base switch (2). Then, it goes
through the switch (3), along the red wire to the tie point to pin 2 of the terminal strip,
and through the limit switch to the motor.
(c) 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.