In/Out (Io Part); Video; Audio For The 2-Scart Version; Program Position With Decoder (Front End) - Hitachi VTMX900EUK Service Manual

9. IN/OUT (IO part)

9.1 Video:

The entire video-I/O is carried out in 2-scart units using the matrix
switch STV6401 [7904), which is controlled by the AIO via the IIC
bus (SDA,SCL). To do this, the following signals are connected to
STV6401 at the inputs: VFV-pin4, VIN1-pin6, VIN2-pin8, VOUT
pin10 ( 1) The VOUT signal is also passed through a voltage divider
and a low pass [2906,3934,3928] and passed to the modulator
where necessary via the emitter follower [7909]) and VFR-pin12
(front cinch input). The outputs OUT3/pin15 (scart 2) and OUT2/
pin16 (scart 1) in the IC are fitted with a 6dB amplifier and convey
the signal to the relevant scart socket. OUT1/pin2 has no amplifier;
this signal (VBS) is passed on to the VS circuit parts for further
processing:
In 1-scart units the SE IC [7004] selects the input video. SE IC
original layout: VIN1 (the VBS line is used in the plan) pin 38 , VFV
pin 36. The VOUT1 signal (scart 1 video out) is generated using an
E-follower [7908] from the VOUT signal.

9.1.1 Audio for the 2-scart version:

9.2 Decoder mode:

9.2.1 Program position with decoder (front end)

The front end signal (VFV or AFV1/2) is passed to the decoder
connected to Scart 2 and from there, goes back to the VCR via
VIN2 or AIN2L/AIN2R .
External input with decoder (9.2.2) is not possible for these pro-
gram positions.

9.2.2 External input with decoder

The signal from scart 1-in (normally TV set) is passed to the
decoder connected to scart 2. For scrambled programs, the
decoder switches the pin 8 to high. The VCR then passes the
decoded signal from scart 2-in to scart 1-out.

10. Follow Me (FOME part)

This circuit is used to compare the front end video with the video on
scart 1 (video from the TV connected) in order to be able to save
the stations in the same order as on the TV.
The video signals from the front end (VFV) and from the scart
socket (VIN1) are "digitised" using filters and comparators [7530-C,
7530-D] and compared with one another [7531, 7532, 7530-A].
Low on the output for the circuit means that the picture contents for
the two video signals are identical and that both receiver parts (TV
and VCR) therefore have to be adjusted for the same station.
Possible errors detected may result with similar signals, e.g. news
programmes.
11. VPS/PDC, on-screen display
(VPO part)

11.1 VPS/PDC

The VPS and PDC data is either decoded by the VPS-PDC
decoder-IC SDA5650 [7502] or by the OSD-IC with integrated
1)
-
VPS, PDC decoder SDA5652 [7502]. Both ICs are compatible in
terms of pins, despite any differences in the peripherals.
The VPS-PDC data are read from the vertical blanking gap and
stored in the internal RAM. This data is read from the µP via the I²C
bus.
The time can also be read from the TXT header line (required for
"Time download"). The date is not called up from the TXT header
(various write versions of the preset stations) but only via PDC
format-1.
In the case of the SDA5650 [7502] the input video signal comes
from the signal electronics IC LA71595M [7004-B pin 32] (VREC)
via a 470n capacitor [2504] to the data slicer input on the SDA5650
(pin 17). For the SDA5652 the input signal from pin 29 (VSB) on the
LA71595M [7004-B] comes via an emitter follower [7501] with a
voltage divider to the data slicer input on the SDA5652 (pin1 17).

11.2 OSD-PART

The IC SDA5652 [7502] also allows both the generation of text
keyboard matrices into a video signal and the generation of an
entire picture (full page) for menu-control or if no background video
is available.
The video signal (VSB) passes from the signal electronics IC
LA71595M [7004-B pin 29] via a resistor [3512] to the input for the
OSD-IC [7502 pin 18]. For keyboard matrices in Secam video
signals, a bypass between video-in and video-out is activated via a
switch inside the IC and a band filter [2507, 5502]. The output
signal is available on pin 15.
A multiple of the doubled colour subcarrier oscillation from the
signal electronics (2FSC/8.86MHz) is used as the system pulse for
the IC. It is also used as a reference for generating the various
OSD colours. The signal reaches the IC via a coupling capacitor
[2509].
For the vertical synchronisation of keyboard matrices, an OSD
frame pulse (OFP) is generated by the µP [7899-B pin 36] and
passed to the IC [7502] on pin 9. The horizontal sync-pulse is
generated using an internal sync-separator and an internal H-PLL
from the video signal on pin 17.
During full-page OSD (menu or no video) neither a vertical-sync
(OFP) nor an H-sync is required, as in this mode, the OSD-IC
generates everything from the system clock frequency, i.e. all the
necessary pulses are generated internally from the 2FSC signal.
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