Akai VS-2EGN - Page 24

Upon swing pulse input from IC9 pin (1), -90° phase-
shift is effected every 1H at CH-2, and CH-1 does not
make phase rotation. This method is totally identical
with that of recording. However, since the difference
component of the two inputs is extracted at the balanc-
ed modulator of IC10, the 90° shift is cancelled.
1C10 pin (8 signal phase. . —90°. BAL °
C10 pin (4) signal phase .. -90°——>| Mop ~°
5) PALDOC
When the PB output becomes very small due a cause
such as tape damage, during playback, or when there is
no output, a PB signal of 1H length only is used as com-
pensation. This is obtained by using a 1H delay line.
In the CHROMA system, as a drop-out occurs, IC9 pin
becomes ‘L’, HD output from pin stops, PB
Burst is no longer output from IC10 pin(3), and Colour
Killer output CK-1 from IC11 pin becomes ‘L’.
The output of IC8 (AN6363) pin becomes ‘H’,
TR57 is actuated via D14, the delay line of DL2 is put
into the PASS condition. Though the output frequency
2-2-3
RECORDING
AND
PLAYBACK
OF
SECAM
B/G
1) SECAM B/G recording
Rec BG SECAM chroma
SIGNAL IN
fse= 272 fH=4,25MHz
tsR = 282fH=4.40625MHz
fH= IS625Hz
of the XVCO becomes unstable, since the phase rotation
stops, the CHROMA phase remains locked.
Since D10 makes pin ® ‘H’ during recording, the DOC
circuit does not operate.
6) NTSC 4.43 PB AFC
This is basically the same as PAL, and AFC operation is
performed at IC9 (AN6362).
It differs from PAL in that 40 fH=629.37056 kHz is
selected by the switching circuit composed of TR46 and
TRA47 and is fed to IC11 pin@). The APC system is the
same as the PAL APC system,
When phase differences occur between the PB Burst and
the XO which cannot be followed by the APC system,
an ID pulse is generated from IC11 pin (i). This ID
pulse enters IC9 pin , causes the control circuit to
effect —90° shift of the 90° rotation selector circuit,
and changes the phase of the 40 fH being output from
pin (). This shifts the phase into the range that can be
followed sufficiently well by the APC system.
1c 10 fsptow = 810.57212 KHz
(oon ea)
>t
ino
(?
>
SECAM
BG
chromo
OUT
yan
Low frequency converted
fsriow = 654.32212KHz
1c8
fs+(40+1/8)fH=5,060572IMHz
Fig. 7-13 SECAM B/G Recording—Frequency Conversion
SECAM B/G (Middle East SECAM): CHROMA record-
ing
@) Low frequency converted CHROMA signal is
generated by the down system.
® Neither CH1 nor CH2 are subjected to phase rota-
tion.
A SECAM B/G signal which has been fed to IC10 pin)
through FL16 (4.43 MHz BPF) emerges from pin (2) by
passing through the balanced modulator circuit with the
6 dB UP/DOWN unaffected.
Afterwards, the signal is fed to pin through FL14
(1.5 MHz BPF) without being affected by’ D30 since
D30 is cutoff because the PAL/SECAM/4N-H line is
‘H’. It emerges from pin.
This low frequency converted SECAM CHROMA sig-
nal passes through the trap circuit (L4 and C10) without
being affected by it, is level-adjusted at VR2, mixed with
FMY, sent to the pre-amp, and to the video head record
circuit.
Since the SD-H line is ‘H’ as this is the due to SECAM
mode D16 conducts. As a result, the phase rotation con-
trol circuit of IC8 (AN6363) stops the phase rotation of
the CHROMA signal.
At this time, the ACC circuit located between pin ®@
and pin @ controls the burst level by sampling the line
burst signal by means of the BURST GATE pulse gene-
rated at HD.
The BURST signal from IC10 pin(3) becomes high via
D22, since the emitter potential of TR58 is SB-H (‘’
during SECAM B/G ) mode. As TRS8 becomes cutoff,
the BURST signal is no longer fed to IC11 pin (4),
and the APC loop is not formed for either recording or
playback.
————
Service
Manual
VS-2EGN
———
$S—$—5—
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