(5) Reclining the back. Zero voltage is applied to the back adjust motor as it
is applied to the seat adjust motor. 120v is applied through the mode switch to the
common of the back adjust switch, pin (2). The switch is pushed to the back position
bringing 120v through switch, pin 3, out the blue wire to the junction box. Out of the
junction box at terminal strip pin 4, power is applied to the back windings. It energizes
the motor and reclines the back.
(6) Tilting the back up. Power is applied to the common of the back adjust
switch through the junction box and the mode switch. When the switch is depressed to
the forward position, power is applied through switch pin (1), out the white wire to the
junction box to the manual up windings. It energizes the motor and brings the chair
forward.
b. Automatic Mode Circuit Description. Refer to figures 2-1 and 2-2.
(1) The automatic control board. The control board is located underneath
the footrest on the bottom of the seat itself. The board contains the control circuit
consisting of transistors and three operational amplifiers driving four relays. There are
(3) potentiometers used in conjunction with the control board. They are located on the
back of the chair to allow access for the doctor or assistant to preset to a desired
position.
(2)
Operate mode.
(a) L1-L2 power is applied across the primary of T1. T1 secondary is
rectified by CR17 and CR19 to 32vdc (volts direct current). This is applied across C1
and CR2 regulates V1 output to 15vdc. This is the power supply for the control board.
(b) When switch "A" is depressed, a positive pulse is applied to the
base of Q2. Its collector goes low and is applied at the base of Q14. Q14's collector
goes high. This high is applied to the base of Q1. When Q14 conducts, C16 is charged
to approximately 24vdc. CR1 conducts at 15v and regulates V2 to 14.3vdc V2 is the
power supply for A1. It also generates a voltage for A1's non-inverting inputs.
(c) The setting of R36, R37, and R38 (located on the back of the chair)
determines the reference voltages comparators A1.1, A1.2, and A1.3. Using A1.1 as an
example, the voltage on the center tap of R36 is the reference or position control
voltage applied on the non-inverting input (pin 3). This voltage is always positive in
practice.
(d) R11, C3, CR4, and R12 form a time constant network. Before V2 is
applied to this network, C3 has discharged through CR4, R11, and R12. Therefore,
when V2 is first applied, pin 3 of A1.1 (from R36) is much more positive than pin 1 (from
C3). The output, pin 1 of A1.1, goes high, turning Q10 on, energizing K1, causing the
seat tilt motor to run. The high output at pin 1 of A1.1 also forward biases CR14 and
latches Q2 on through R10 and R45.
MD0373
2-6
Previous Page
