Initial Power Reset Circuit - Teac C-1 Service Manual

TAPE TRANSPORT SECTION
2. CONTROL P.C.B.
2-1 INITIAL POWER RESET CIRCUIT
The initial power reset circuit is provided to prevent the
SYS-CON from being operated mistakenly by transient
phenomena which takes place when the power switch of
C-1 is turned on. (Refer to Fig. 8)
When the power switch of the tape deck is tumed on, the
regulator on the power supply PCB operates and 13V DC
is supplied to the control PCB. At the same time, current
flows in C517 via route (1) and charges it and then Q517
turns on. Then, the base current of Q516 flows in route
(2) and Q516 also turns on and supplies a high level reset
signal to the SYS-CON in the route (3).
This reset signal resets operation memories and counters
in the SYS-CON.
After C517 has discharged, Q517 and Q516 turn off and
the reset signal supply is stopped.' The reset signal is issued
for about one (1) second after the power switch is turned
on. When the power switch is turned off, C517 is rapidly
+13V
discharged and prepares for the next turning on of the
power switch. When the power switch is turned on with no
cassette loaded in the tape deck, Q516 is turned on conti-
nuously by the current in route (5) and SYS—CON is left
in the reset status. The reset status is released by loading a
cassette. If the power supply voltage of the control circuit
fluctuates, unnecessary operations may take place owing to
different charging and discharging time constants or the
threshold voltage of circuits driving solenoids and LEDs.
To prevent such unnecessary operation, the circuit com-
prising D539, Q514 and Q515 keeps inputs of these drive
circuits at a low level when the power supply voltage is too
low. When the power supply voltage is below about 8V,
Q514 turns off and Q515 turns off so they inhibit opera-
tion of the drive circuits so that solenoids and LEDs are not
turned on.
TO AMP.(REC MUTE SIG.)
- TO REC MUTE LED DRIVER
TO AMP(REC SIG)
TO REC LED DRIVER
TO SOLENOID DRIVER
TO SOLENOID DRIVER
TO PAUSE LED DRIVER
} TO REEL MOTOR DRIVER
SYS-CON
U501 R548
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RES K) |
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SYS-CON OUTPUT INHIBIT CIRCUIT
OURING TAPE LOADING
REFER TO 2-3
ON OFF
°° O
CAPSTAN MOTOR SW
S693 r y ¥ © @s
D545
@ T-1296
Fig. 8° Initial Power Reset Circuit