Jvc BR 6400 TR Service Manual Part 2

Page 1

3-50

(1

(2

(3

(4

(5

) |C2-1,2, 13 (SUP. TENSION)
ON when the tape is wound around the drum.
The tension servo works on the SUP. side from
the differential transformer through IC1.

lC2-3, 4, S (REEL UN L)

ON during unloading to supply the SUP. motor
with the pedetermined determined by R32.
By this switch operation, the speed of un-
loading tape is wound faster than that of the
tape returning into the cassette in order to
avoid the slack oi the tape.

lC2A6, 8, 9 (REEL REWl

ON in the REW mode to apply the speed servo
on the SUP. side from the photoAinterrupter
through |C1O and 11.

|C2-10,1112(F1EEL LOAD)

ON in the Loading mode to supply to the SUP.
side the ore-determined voltage determined by
R29. By this switch operation, the back tension
during the loading is determined.

Ice-1,2, 13 (REEL FFl

ON in FF mode to amplify the T.U. motor
terminal voltage. applied at the inverse input
pin @of lC8, and to return this voltage to the
inverse input pin of comparator |Cl2 as a
voltage feed back signal for the speed servo. In
FF and REW mode, the tape winding speed is

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one.

(6

(7

l8

(9

so fast that the voltage control is used in speed
control to complete the FF or REW in the
speed specified for the respective tape,

ICQ-3, 4. 5 (REEL REW)

ON in the REW. This switch applies the voltage
feed back, which is the same as the case of
ICQ-l, 2, 13.

lC9-6, 8, 9 (REEL REW)

ON in all the mode but REW mode, Utilizing
the voltage drop due to the motor current
which flows the resistor R154 of 0.47 ohm, the
current feed back of SUP. motor is applied to
the inverse input pin®of lCB. and is returned
to the pin®of 1C7 after being amplified.

In the other modes than FF and FlEW mode,
the tape winding speed is slow and it is intend-
ed to control the tape tension. So. the motor
torque is controlled by the current.

Ice-10, 11, 12 (REEL FF)

ON in all the mode but FF mode. This switch
applies the current feed back from T.U. motor
to pin®of IC7, in much similar manner as
explained on IC96, 8/ 9. (Detailed explanation
is omitted)

lC14-1, 2, 13 (REEL FF)

ON in FF mode. Apply the speed servo to the
T.U. motor from the photo-interrrupter on
T.U. side through ((313 and 11.

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Feed back circuit

Page 2

(10) lCl4-3, 4, 5 (T.U. TENS, CAP SEARCH)
ON in play and search mode. in these modes,
the ore-determined voltage determined by
R142 is applied to the T.U. side. This is the
winding torque in the general Play mode.

(11) lC14-6, 8, 9 (REEL STILL)
ON in Still mode (including long Still mode).
The voltage, determined by R145, controls the
constant torque of the T.U. motor not to avoid
the tape slack between the capstan and T.U.
reel.

(1)2]1C14-10,11,12(REEL LOAD, UNL)
ON in Loading and Unloading mode. Apply
the pre-determined torque, determined by
R139, to the T.U. motor.
This torque supplements the mechanical brake,
which is already applied.

(13) O1 (REEL LOAD. LONG STILL)

ON in Loading and long Still mode. When the
recorder is stopped while the power being on
for long period of time, the capacitor C10 and
C11 will be so fully changed that it takes time
to discharge these capacitors after loading, and
it takes long for the tension pole to be stabi-
lized. And so, during the unloading, 02 shorts
010 and C11, and also 01 does lC1 pin©and
@in order to apply the optimum tension at
the time of loading by providing the constant
voltage, determined by R167, to pin®of lC1.
Being in the long Still mode, the tape is slack
and the tension pole pushes the differential
transformer core into the coils to fully charge
C10 and 11 (which is the reverse polarity
compared with the above mentioned Stop
mode). 50, pin©and®of |Cl are shorted
during the long Still mode not to change to
capacitor C10 and 11. in order to quickly
stabilize the tension when the mode changes
from long Still mode to Play mode.

(14) 02 (REEL LOAD/UNL, STILL)

ON in Loading and Unloading mode. (Refer to
01) In Search mode, at the time of change over
from REW to FWD or vice versa, the picture
becomes Still mode momentary. Even at this
moment, 02 becomes ON to discharge the long
time constant capacitor C10 and 11 to improve
the tension rising time at the moment of the
change-over.

(15) 05 (DOWN)
In REW mode, this switch becomes ON when
the capstan changes from forward rotation
to backward rotation, and conects the D1
anode to the earth. Input voltage for pin 3
of |Ci decreases with the connection, and the

SUP. motor torque is finally raised higher than
that of the normal Play mode through each
amplifier stage to avoide the picture drop out,
which is apt to occur at the initial portion of
the tape wound around the drum at the time of
REW motion.
This switch also becomes ON in Loading and
Unloading mode, but this does not effect
the torque by the function of other electronic
switches.

(16) lC14-1,2,13 (REEL FF)
Momentary 0N when becoming Still (long
Still) mode, and switches on 02 at that
moment.

(17) 011 (REEL REW)
OFF in REW mode, and switches on the switch
9, 4 and 5 of (CS).

(18) 016 (REEL FF)
OFF in FF mode, and switches on the switch 1,
2, and 13 of (CS.

(19) 012, 018 (ACCESS)

_99 o
_<_l-l_
R EW
0 99

ACCESS command becomes H for -99 to 0 in
FF mode, and for 99 to O in REW mode to
switch on 012 and. 018. The F'V converter
|C1Cl ((613), which uses the charge pump, out»
puts the DC voltage, which is proportional to
the input frequency, but when the capacitor
(347 (C64) is connected paralleled to the charge
and discharge capacitor C46 (C(53). the output
from pin®oi IC10 (pin@of |C13) will rise to
result in the motor speed reduction

In short, during counter Search mode, the tape
speed is reduced between 99 and 0 (-99 and O)
in the REW mode (FF mode) to precisely stop
the reel at near zero point.

The designations and/or numbers given if) the
parentheses are for 018.

(20) 013, 019 (REEL FF, REW)
For approximately 1.1 second since FF mode
or REW mode is taken, H pulse is generated to
switch ON 013 and 019 from the mono-multi-
plexer |C15.
This will raise the output of pin®and pin .of
(011, and cut off the diode DS and D7 to dis-
engage the speed servo loop.

351

Page 49

5.3 SYSTEM CONTROL (SYSCON) CIRCUIT
No. Item (33:: Adlgsatrrrsent Signal Mode Description and Waveform
1 IC14 clock Pin 1 of - - STOP . Connect frequency counter to pin 1 of |Cl4
frequency |C14 and confirm that the frequency becomes 400
Syscon t 2 kHz.
2 lC25clock Pin 1 of - - STOP . Connect frequency counter to pin 1 of IC25
frequency IC25 and confirm that the frequency becomes 400
Syscon t 2 kHz.
3 |C26 clock Pin 30f - - STOP . Connect frequency counter to pin 3 of IC26
frequency K326 and confirm that the frequency becomes 400
SVScon : 2 kHz.
4 Minimum TP-I R22, R24 - STOP .Connect digital voltmeter or oscilloscope to
voltage Syscon Syscon TP»1 of the Syscon board.
.Turn R22 (Minimum voltage) of the Syscon
board to obtain minimum DC voltage.
. Adjust R24 of the Syscon board to obtain DC
voltage of 2.7 t 0.05 V.
5 Still width TP-2 R23 A STOP . Connect oscilloscope to TP-2. Confirm high
Syscon Syscon potential (approx. 10 V DC), If low (about 0 V
_ DC), adjust R23 for high.
' lierform the followmg Steps only-aftercomplet- . Connect a digital voltmeter to TP-l and the
ing item 4, Minimum voltage setting. oscilloscope to TP-2.
. Slowly turn R22 counterclockwise and check
the voltage at TP-l and TP-2.
. If the TP»2 voltage remains high when the TP-l
voltage exceeds 2.95 V. turn R23 slowly
_ Center counterclockwise. Conversely, if the TP-2
VR1 30"9C'05kw'55 _ Clockwise voltage drops low before 2.85 V is attained,
REV STILL FWD turn R23 slightly clockwise.
. Turn R22 clockwise past the center click posi-
tion, then turn it slowly counterclockwise.
TP-1 . Repeat the above steps 4 and 5 so that the TP-2
l ___________ 231° 05 V voltage drops from high to low when the TP»1
i voltage exceeds 2.9 i 0.05 V.
l

TH l
lFlEV CMD) l
I

I

TP-S
(FWD CMD)

Variable by R23

»-:r - 2.7:o.osv
|

. Change the oscilloscope connection from TP-2
. Turn R22 slowly clockwise past the center click

. Confirm that the TP-3 voltage drops from high

to TP-3.

position.

to low when the TP-l voltage exceeds 2.9 it
0.05 V.

575