Sony TC-765 - Page 46

TC-765 |
4. High Voltage Power Supply for Solenoid Initial-
Energization (Refer to Fig. 4)
The solenoids need a high voltage during pulling,
but a low voltage is adequate for hold.
1. When stopped or during tape transport, Q706 is
ON and Q707, 708 are in the OFF state
providing a 12V power supply for solenoid
hold.
2. In the hold condition, as the signal PAUSE (1!)
enters point @ from IC701, Q718 goes to the
ON state and the (+) side of C710 at +24V
suddenly drops to zero potential so that the
(~) side (point @) becomes -24V. Then the
signal passes through R712 and D708 where it
is discharged at a time constant of R712 x
C710.
3. Though Q706 was ON, as the PAUSE signal
enters point @, point @ becomes -24V
which creates an OFF state. Asa result, Q707,
708 are in the ON state and provide a high
voltage power supply for solenoid initial-
energization.
(In this case, turning on playback muting.
Refer to page 11.)
4. When C710 has completed discharging, Q706
goes to the ON state and Q707, 708 go to OFF.
The solenoid power supply returns to +12 V for
hold use.
Q706
ordinarily
in
the
ON
state,
the
O7I7
following
condition
is
necessary.
l2v
D714 is a Germanium diode. To keep
(ee + V709 > V714 + Vee
t2=RT5XCMN3
{
\
|
|
|
!
| A
|
iN
Solenoids |
|
|
|
|
|
|
'
|
\
{
1
|
I
24Vv
tl=RMN4XC713
@ 2v
a ov
Having a time constant
here prevents lamp
flicker from voltage
changes.
PAUSE signal >
made large, the on-time for
1f the value of resistor R775 is
playback muting becomes long.
(t2)
Fig. 4