Sony TC-765 - Page 48

TC-765 |
7. Tape Tension Set-up and Circuit Operation
(Refer to Figs. 6, 7)
In order to make tape tension constant, torque
at the start of tape winding (slow revolution) must be
increased and torque near the end of tape winding
(fast revolution) must be decreased.
1.
B+
At a slow revolution speed, the pulse interval is
long so that the dc voltage output @ becomes
high; hence supply reel motor torque becomes
large.
At a fast revolution speed, the pulse interval is
short so that the DC voltage output becomes
low making the supply reel motor torque small.
Even if the tape speed is varied, if the radius of
the remaining tape is the same, the back tension
has to be the same. Therefore, when changing
from 9.5 cm (3% ips) to 19 cm/s (7% ips) with
switch (S602-1), Q730 is turned ON and half
cycle of the input signal to switching transistor
(Q731) is turned OFF to produce the specified
602-1
TAPE SPEED
9.5cm —= 19cm
torque,
flip-flop schmitt circuit differential amp
9.5cem 19cm
o NIN PALANAN (Output from FG > differential amplifier)
eee piawe ae TU
Os CAs
(Make a square wave by means of the Schmitt circuit}
e S sag a ces RAN } {Constant pulse width attained by flip-flop circuit)
e No output with Q730 ON
lf reel radius is the same, T9.5=T19
7) Senne (Pulse for switching Q731)
T9.5 T19
< is ee a | if reel radius is the same, V9.5=V19
8] V1 Teas vig (Q731 charges at B+ and discharges during switching)
080
SE
_—
_
(DC voltage for motor drive}
Fig. 7