Nakamichi 481, Service Manual

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ference voltage in Fast (FF or REW) mode is
changed. Therefore, re-check of the reference
voltage in Fast (FF or REW) mode is required. If
the reference voltage is out of the range, re
adjustment of R414 according to next step 2) is
necessary.
2) Set the N-481 in FF mode, then adjust the value of
R414 so that the voltage of VR601 will become lower by
1.5 V (±0.25 V) than in stop mode.
3) Press the Pause Switch to set the N-481 in pause
mode.
Adjust the value of R454 to obtain 10 V (+0.4, -0.15 V)
at the sliding contact of VR601.
4) Set the N-481 in playback mode, then adjust the value
of R453 so that the voltage of VR601 will be come lower
by 2.5 V (±0.4 V) than in pause mode.
5) Short the both leads of capacitor C406 with a jumper
wire.
Set the N-481 in record mode, then adjust the value of
R419 so that the voltage of VR601 will become higher
by 1 V (+0.4, —0.2 V) than in stop mode.
Note: Remove the short of C406 after completion of
adjustment.
(3) Cam Timing Adjustment
(a) Remove the wires from the Control Motor terminals to
set the motor open.
(b) Without loading a cassette tape and with pressing the
record protecting switch with your finger tip, press the
Record and Play Switches to set the N-481 in record
mode.
(c) Turn the Cam and bring the “PY” mark toward the
pointer by hand.
Reel Motor will rotate before the “PY” mark reaches the
pointer.
Adjust the value of R436 so that the voltage at the
sliding contact of VR601 becomes 9.7 V (±0.3 V)
when
Reel Motor starts rotation.
(d) Observe the mute signal at the Q416 collector.
Turn the Cam referring to above step (c) and check to
insure that the voltage at the sliding contact of VR601 is
9.5 V (±0.3 V) when mute is released (mute signal
changes from H to L).
(This voltage is determined by the adjustment of R436
in above step (c).)
(e) Observe the (Play + Pause)—Position signal at the
Q411 collector.
Turn the Cam referring to above step
( c) and adjust
the value of R432 to obtain 11.2 V (±0.4 V) at the
sliding contact of VR601 when (Play + Pause) —
Position signal changes from L to H (bias oscillation will
begin).
(f) Upon completion of above adjustment, re-connect
wires to the motor terminals.
5.2. Tape Speed Adjustment
(1) Remove the Top Cover.
(2) Connect a Frequency Counter to the Output Jack.
(3) Load a 3 kHz Speed Wow/Flutter Tape (DA09006A)
and play it back.
(4) Referring to Fig. 5.3, adjust the Tape Speed
Adjustment Volume (VR501) incorporated in the
Capstan Motor to obtain 3,000 Hz on the Frequency
Counter.
CCW: Motor drives slowly.
CW: Motor drives fast
.