TANDBERG TCD 310 Service Manual

4.2 A SHORT EXPLANATION OF THE
MOTOR CONTROL CIRCUITS
When the reel motors revolve, they generate pulses.
These pulses are used to control the motor power
supply.
When both motors are stationary, no pulses are fed
to the motor signal amplifier. Q504 of the Schmitt-
trigger is cut-off, and Q505 is conducting. Q507 is
also conducting, and the motor power supply is
connected to ground. Therefore, no voltage is fed
to the motors.
When the REWIND, WIND, PLAY or RECORD
button is depressed, one of the capacitors C317,
C320 or C321 will give a trigger pulse to the
Schmitt-trigger. Q504 starts conducting and Q505
goes cut-off. Q507 also goes cut-off, and the motor
power supply feeds a voltage to the motors (via
microswitches and operating switches). ‘The motors
start revolving, feeding pulses to the motor signal
amplifier. The output from this amplifier will keep
Q504 in conducting state.
During wind or rewind the supply motor works as
a generator, feeding a negative voltage to transistor
Q506, which regulates the motor power supply.
The voltage from the power supply is therefore
dependent on the speed of the supply reel.
When the tape stops (for instance at the end of the
tape) the input to the motor signal amplifier drops
to zero, and the Schmitt-trigger reverts to unope-
rated state after a short delay (determined by
C508/R512). Q507 starts conducting and the
voltage from the motor power supply drops to zero.
4.3 CONTROL OF MOTOR VOLTAGES
Remove the bottom plate, insert a cassette in the
deck and check that the voltages across the motors
are as specified below:
OV
0.7V~0.8V | 0.7V—-08V
Drops to 0 Drops to 0
after a short after a short
while while
10V~3.5V
Drops to 0a
little while
after the end
stop is reached
10V—3.5V
Drops to 0a
little while
after the end
stop is reached
Block diagram of motor control circuits
13

TANDBERG TCD 310 Specifications

General

Weight	7.5kg
Track System	4-track, 2-channel stereo
Tape Speed	4.76 cm/s
Heads	1 x record/playback, 1 x erase
Type	Cassette Deck
Frequency Response	30 Hz to 16 kHz (Chrome tape)
Signal to Noise Ratio	58dB
Wow and Flutter	0.07 %
Motor	DC servo motor
Tape Type	CrO2
Power Supply	220V
Input	Line In