Learning Event 3:
FUNCTIONS OF THE CAPSTAN PHASE
SERVO/RECORD AND CAPSTAN PHASE
SERVO/PLAYBACK CIRCUITS
1.
The phase servo has different loops in the record mode and playback mode. In the record mode,
the phase loop adds to the speed servo in order to eliminate drift in the speed servo system. The
positive-going 360 Hz FG pulse is doubled twice and divided by 48 which provides a 30 Hz pulse which
is then integrated to form the 30 Hz ramp waveform. The 30 Hz reference signal samples the positive
slope of the 30 Hz ramp. The output of the sampling circuit goes to the HOLD capacitor to produce the
DC output. The DC output is phase-inverted, amplified and goes to the capstan motor. IC-1 has an
operational differential amplifier in its final stage. The sampled DC outputs of both the capstan speed
servo and phase servo go to the differential amplifier inputs. If the capstan motor speed decreases, the
FG signal phase retards with respect to the other 30 Hz reference signal. This produces a reduced
sampling DC output, which increases the differential amplifier output and accelerates the motor.
2.
The phase of the 30 Hz reference signal changes in order to change the phase relationship
between the playback CTL signal and the 30 Hz reference signal. The TRACKING one shot performs
phase adjustment which is controlled by the TRACKING CONTROL on the front panel. When the
FWD button is off, the capstan motor driver mutes so that the motor stops.
3.
The FG dividing counter is reset by the CTL signal in the playback mode so that the 30 Hz FG
signal will be positioned very close to the CTL SIGNAL. This is necessary since the servo reference
signal changed from the CTL signal to the 30 Hz FG signal in the ASSEMBLY edit mode and the servo
system is put into the record mode from the playback mode. The 30 Hz FG is close to the CTL signal in
order to minimize the lockup time in the servo loop.
4.
There are two rotary erase heads, one for each of the two video heads, each just ahead of the
video head on the drum. In the Insert mode of operation, these rotary erase heads pre-erase the recorded
track on the tape just ahead of the new recording. This permits erasure and recording of only the exact
number of previously recorded slant tracks corresponding to the length of the edited segment. In the
assemble mode of operation the rotary erase heads turn on but only work during the initial five seconds
after the assemble mode starts. This is to erase the video information in the segment of the tape between
the fixed, full-track erase head and the head drum.
Learning Event 4:
FUNDAMENTALS OF THE AUDIO (AU-8) AND POWER SUPPLY CIRCUITS (PW-1A)
1.
Refer to Figures 5-2 and 5-3 (fo) at end of lessons. There are two identical audio record and
playback channels to accommodate stereo or bilingual audio. In playback, both channels are operational
and supply outputs are at the Ch-1 (left) and Ch-2 (right) jacks on the rear panel. In addition, the
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