Nakamichi 481 Service Manual - page 16

15 

2.3.7.  Control Motor Drive Circuit 

Refer to Fig. 2.3.10 circuit diagram and Fig. 2.3.11 timing 

chart. The control motor is turned by varying amounts, 

according to which control button is set. This motor is 

connected to the mechanism control cam, and the 

mechanism is set to the mode indicated by this cam. 

The motor is driven by the differential amplifier IC402 (1/2) 

and drivers 

Q405 and Q406. In the control motor stop 

condition, both voltages at pins No.5 (non-inverting input) 

and No.6 (inverting input) of lC402 (1/2) are equal and the 

difference of both inputs is zero. When a new mode is 

demanded, the balance of both inputs is broken, as a 

result, the control motor is driven until both inputs are 

balanced. The cam control variable resistor VR6

01 

moves synchronously with the motor so that the voltage 

at the sliding contact of VR6

01 is changed. 

When the voltage at the sliding contact of VR6

01 is 

changed and the input difference of the differential 

amplifier IC402 (1/2) becomes zero, the control motor 

stops. 

The following table shows the relationship between cam 

position and the voltage at the sliding contact of the cam 

control variable resistor VR6

01, and the state of transis- 

tors in each mode. 

Position on 

Cam 

Typical Voltage at Sliding Contact of 

Corn Control Volume 

Record 

Stop 

FF/REW- 

Pause 

Play 

16V 

15V 

13.5V 

I0V 

7.5V 

Mode ON 

OFF 

Record 

Stop 

FF/REW 

Play/Pause 

Play 

Q403, 

Q410 pulse     Q412 

      Q412 

Q404, Q410   

      Q412 

D417 ON 

      Q411, Q412

                    Q411 

Q404 

   Q411 

Q403, Q404,Q410 

   Q411 

Q403                             Q411 

Q403, Q404, Q410   

Q403, Q404, Q410     Q412