Tascam 122 Service Manual page 12

122
U601
PLAY 12
OUT o.::....R"'
6 1 2
PAg~~ (j-
r - - - - - , r - - - - - - - - - - - - l
I DRIVER I I FLASHING CIRCUIT I NO LOAD)
..-14-- - - - - -
+ 13 V
I
I
I
R!l39
I
R618
I
11r--1
I Q514
I
L ___
- I--J
R538
"'..J..M~-..--H
R6 1 3
Q601
I
C!lI!I
0508 R534
R610
+ - - --llf--_.......
--"/.(r-...._--H
HEAD BASE
T
SOLENOID
I
O!l09
L692
069 4 1
I
I
L _ _ _ _ _ _ _ _ _ _ _ _
.-J
Fig. 3·5 'Head base solenoid drive circuit
3·3-4 Pinch roller solenoid drive cia:uit
See Fig. 3·6.
The pinch roller drive circuit (drive
& flashing
circuit) operates basically in the same way as
the fast solenoid and head base solenoid drive
circuits and, therefore, the description is not
repeated. Since the mechanical load of the pinch
roller solenoid is low, the flashing interval is
100 msec which is provided by capacitor C508
and resistor R 521.
Here, operation of the power delay circuit and
reproduce delay circuit are described as they are
not incorporated in solenoid drive circuits.
1) Power delay circuit
The positive side of capacitor C526 is con·
nected to the output of the +23 V voltage
regulator. This regulated +23 V is used as the
power source for the amplifiers and also as a
reference voltage for the power supplies
which supply the control circuits, reel motor,
12
and capstan motor, etc., with DC power.
(These power supplies are described in 3·8·2.)
When power is turned on, the tape might
become slack or run unevenly if the repro·
duce mode is entered before the +23 V is
stable. The power delay circuit delays the
operation of the pinch roller until the DC
supply voltage
~
ises to a steady level after
power is switched on. This circuit operates
as follows.
a. When power has been turned on, the +23 V
regulated power supply starts to work and
its output voltage rises.
b. As the output voltage rises, base current
flows through transistor 0521 via capacitor
C526 and resistor R547, turning it on.
c. As 0521 is on, base current flows through
transistor 0508 and turns it on.
d. As 0508 is on, the base and emitter of
pinch roller solenoid driver transistor 0509