Fostex B-16 - Page 15

to comparator U13-9. Output 013-8 which is compared with the reference voltage
U13-10 is smoothed by the integration circuit consisting of R142, R143 and
C35, passed through Q28 and applied to the DC amplifier. This is then current
amplified by Q29 to control the capstan motor.
When Q29 switches OFF, Q30 switches ON to absorb the inverse electromotive
power from the motor which thus serves as a braking circuit.
4.5 Solenoid intermittent circuit
There are two plunger solenoids in this transport. One is used to draw in
the pinch roller and release the brakes when in the PLAY mode. The other is
used to push out the tape lifter and also release the brakes during the FAST
WINDING modes.
When the PLAY button is depressed, U9-11 goes to "H" level and this signal
passing through the differential circuit of C23 and R78, momentarily switches
on Q6 for a duration of 5 % 10msec.
when Q6 switches ON, C24 is discharged and when Q6 switches OFF, the signal
passing through the integration circuit of R81, C24 and R83, momentarily
switches on Q7 for a duration of 100 180msec. By switch ON of Q7, QB is
switched ON and +26V is applied to the solenoid. Then, at the moment QB is
switched OFF, +13V is applied to the solenoid via D68. During this time, at
about the same instant that U19-11 goes to "II", 07-12 also goes to "II", and
as Q9 and Q10 is already ON, the PLAY solenoid will be activated.
In the same way, when the transport is put in the FAST WINDING and EDIT
modes, 09-4 goes to "H" , and by charging of C22, +26V and +13V are applied
to the solenoid, Qll and Q12 are switched ON and the FAST solenoid is
activated.
4.6 Counter section
The major component of the counter circuit in this system is the P-MOS
type LSI, 023.
1) Count pulse input circuit
In the following is explained the circuit from count pulse detection up
to the UP/DOWN input and COUNT input of U23.
The circuit and timing chart is shown in Fig. 4.3. The frequency divider
circuit have been omitted for simplification.
Linear tape motion is transferred to the footage roller, at right side
of the transport, by rotating it. This rotation is detected by two photor
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