User manual NAKAMICHI 481 SERVICE MANUAL

[. . . ] General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Principle of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Headblock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [. . . ] These signals are amplified into square waves, and transmitted to the shut-off detecting circuit in the subsequent stage. When the tape-end comes, the take-up reel and the disc stops rotating, and no pulse is output from the sensor. (2) Shut-off Detecting Circuit and Peripheral Circuits Shut-off conditions are as follows: o reached tape-end during PLAY (PLAYBACK or RECORD), FF, or REW mode o mode is changed as follows: from FF to REW mode, or vice versa from FF to PLAY mode from RECORD mode to FF or REW mode When the mode is changed, shut-off is momentarily activated and the mode is changed to STOP mode in a short period of time, and after this STOP mode is over, a new mode is set. 0 Power-mute = L pulse is generated when Power Switch is turned ON or OFF 0 memory rewind function is activated. 11 (a) Reached tape-end during PLAY (PLAYBACK or RECORD), FF, or REW mode Explanation is made for PLAY mode as an example. For FF or REW mode, the shut-off function is the same as for PLAY mode. Accordingly, R488 (100 kohm) is grounded through Play Button and the voltage at the point A becomes approx. Since the voltage at the point A is not lower than the emitter voltage of Q424, Q424 is turned OFF and Q426 is also turned OFF. (Q424 and Q426 will be turned ON when the voltage at the point A is further lowered as described in subsequent (b). ) Q425, Q427, Q430, R470 and C412 consist of a shut-off detecting circuit. therefore, Q425 is turned ON and C412 (2. 2 pF) is charged toward +24 V through R470. Meanwhile, pulses from the shut-off sensor are applied to the base of Q427 through R489 and C418, and, at every H cycle of the sensor output pulse, Q427 is turned ON and C412 is discharged through Q427. When the tape-end is detected, pulses from the shut-off sensor are not transmitted and Q427 is turned OFF, resulting in C412 being charged continuously. When the voltage of C412 exceeds the sum of the emitter voltage (approx. 5. 5 V) and the VBE of Q430, Q430 is turned ON and the base current flows to 0429. Con -sequently, Q429 is turned ON, Q428 is cut off, +24 VS is shut-off, PLAY mode is changed to STOP mode, and play lamp goes out. Q430, Q429, Q428, R476, R474, R456 and C420 consist of a Schmitt circuit which provides hysteresis characteristics for ON/OFF of Q430. Accordingly, Q430 will be turned ON or OFF without chattering for the input waveform with a large time constant developed across C412. If Pause Button is pressed during PLAY mode, tape stops and no pulse is transmitted from the shut-off sensor, but Q427 is kept ON since Q423 is turned ON during PLAY. PAUSE mode, therefore, no charge is made at C412 and shut-off is not activated. When shut-off is made at the tape-end during PLAY mode, PLAY mode is changed to STOP mode. If Stop Button is further pressed, Play Button will be re leased and the voltage at the point A returns to +24 V as R488 is released from grounding, as a result, Q425 is turned OFF and C412 is discharged quickly through D423 and R467 (10 kohm). Accordingly, Q430 is turned OFF, Q429 is turned OFF, Q428 is turned ON, and +24 VS is again applied preparing for the next control button operation. (b) Mode is changed 1) From FF to REW mode, or vice versa, or from FF to PLAY mode Refer to Fig. When mode is changed from FF to REW mode, or vice versa, or from FF to PLAY mode, momentary STOP mode is automatically taken in view of the response of the tape deck mechanism, and after this is over, a new mode is set. The following explains in regard to the case when FF mode is changed to PLAY mode by pressing Play Button during FF mode: During FF mode, R486 (100 kohm) is grounded by the NOT Kf. f. When Play Button is pressed, it is locked ON and FF Button is released. [. . . ] While modifying an EXII C-90, the tape guides in the cassette housing shall be kept protected to avoid tilt. Check shall be made in the following procedures: (1) An EXll C-90 Tape thus modified shall be loaded onto the N-481. (2) Release the back-tension (rotate the Supply Reel and feed out some length of tape) and set the N-481 in play mode. (3) In this juncture, check to insure whether the tape is free from waving or slippage from the tape guide. [. . . ]