Color Signal Playback System - JVC HR-S10EG Service Manual

1.6 COLOR SIGNAL PLAYBACK SYSTEM
The color signal playback system performs essentially the
opposite function as the recording system. In addition, how-
ever, important corrections must be performed for color
signal frequency and phase errors introduced by variations
in tape speed and head rotation, and elasticity of the tape.
Fig. 1-15 indicates an abbreviated block diagram of this
system.
Through a lowpass filter, the down converted color signal
goes to the main converter, At this time, the down con-
verted color subcarrier (Fc) contains an error component
{40Fh' + 1/8Fh' + Af) due to mechanical factors of the
heads and tape. Fh' varies with the tape speed as Fh + AFh.
Af is the instantaneous error caused by head rotation irregu-
larities and tape elongation and contraction,
Correction of the color time axis is performed using two
two types of data. These are 1) color burst signal phase and
2) horizontal sync signal frequency.
In the first loop, the burst component is separated from the
color signal and compared with a reference frequency.
Azimuth video
head + 6°
---Luminance signal playback system -----.
!= 4OFh +1/8Fh' tAt fy
PHASE SHIFTER
I60Fh
vco
The second loop separates the horizontal sync signal from
the video signal for comparison with the output of the
160 Fh VCO (voltage controlled oscillator).
The outputs of the above loops are mixed and control the
160 Fh VCO, The VCO output is counted down and
applied to the phase shifter.
The phase shifter is controlled by the 25 Hz field pulse.
Its output is the converter carrier (Fs + 40 Fh' + 1/8 Fh' +
Af), which includes the phase and frequency error com-
ponent.
By frequency conversion with Fe, the color subcarrier fre-
quency of 4.433619 MHz, which is free from frequency and
phase deviations, becomes obtained through a bandpass
filter. In the opposite manner as with recording, the phase
shifter advances the CH-2 track phase 90° every line and
40 Fh' is supplied to the sub-converter. The playback color
signal through the main converter and bandpass filter is
applied to a 2H delay line for removing crosstalk. Charac-
teristics of the lowpass and bandpass filters are the same as
those for recording (Fig. 1-15).
At the mixer, the playback color and luminance signals are
mixed to become the video output signal.
Video output signal
(Color TV signal )
Fig. 1-15 Color signal playback system
1-9