Nakamichi 481 Service Manual - page 27

5.1. Mechanism Control Cam Adjustment 

Before Adjustment, disassemble the Front Panel 

Ass’y then remove the Cover Plate Ass’y, referring to 

items 3.4 and 3.14. 

(1) Offset Adjustment of Control Motor Driver 

(a) Refer to Figs. 5.1 and 5.2. 

Adjust VR602 and VR603 on the Control P.C.B. to 

locate approximately at the middle of the variable range. 

Then turn ON the Power Switch. 

VR602 (for Cam position stop) 

VR603 (for Cam position play) 

(b)  Press the Stop Switch to set the N-481 in stop mode. 

Adjust VR602 (for stop) so that the “S” mark on the 

Cam corresponds to the pointer on the mechanism 

chassis. 

(c)  Press the Play Switch to set the N-481 in playback 

mode. 

(Cam will rotate, and the position marked with “PY” 

comes to the pointer.) Adjust VR603 (for play) so that 

the “PY” mark on the Cam corresponds to the pointer. 

(d)  Repeat above (b) and (c) 2 — 3 times so that the “S” 

and “PY” marks on the Cam correspond to the pointer 

accurately in stop and playback modes respectively. 

(This adjustment is required because the position 

adjusted by one volume will be slightly changed when 

the other volume is adjusted.) 

(e)  Set the N-481 in FF, pause, or record mode by pres 

sing each switch and check to insure that the pointer is 

in a range of “F”, “PS”, or “R” mark respectively. 

(f)  If out of the range, precise adjustment for each position 

according to “(2) Offset Fine Adjustment of Control 

Motor Driver” will be required. 

(2) Offset Fine Adjustment of Control Motor Driver 

Adjust only if a satisfactory result is not obtained in “(1) 

Offset Adjustment of Control Motor Driver”. This adjustment 

is made by changing the value of the fixed resistors on the 

Main P.C.B. 

Note:  The value of voltage is typical value. 

(a)  Observation Point of Reference Voltage Observe 

the each voltage at the sliding contact of the Cam 

Control Volume VR601 (10 kohm) in stop, fast (FF or 

REW), pause, record and playback modes. 

Note:  When Record and Play Switches are pressed to 

set N-481 in record mode, the Cam is first set to 

the record position in a short period of time then 

stays at the play position. Therefore to keep the 

Cam at the record position, following procedure 

is required: 

Short the both leads of capacitor C406 

(2.2 uF) on the Main P.C.B. with a jumper 

wire, then press the Record and Play 

Switches. 

(b) Reference 

Voltage 

Reference voltage at the sliding contact of VR601 

(Cam Control Volume) in each mode is as follows: 

(d) Adjustment 

Procedures 

1)  Press the Stop Switch to set the N-481 in stop 

mode. 

Adjust the value of R415 and R416 to obtain 15 V 

(±0.6 V) at the sliding contact of VR601. 

Note: When R415 and R416 are adjusted, the re- 

5.  MECHANICAL ADJUSTMENTS 

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