Video Switch Tea6415; Multi Standard Sound Processor; Sound Output Stage With Tda7480L; Vertical Output Stage With Tda8177F - Toshiba 29VH27E Service Manual

4.VIDEO SWITCH TEA6415

In case of three or more external sources are used, the video switch IC TEA6415 is used. The main
function of this device is to switch 8 video-input sources on the 6 outputs.
Each output can be switched on only one of each input. On each input an alignment of the lowest level
of the signal is made (bottom of sync. top for CVBS or black level for RGB signals).
Each nominal gain between any input and output is 6.5dB.For D2MAC or Chroma signal the alignment
is switched off by forcing, with an external resistor bridge, 5VDC on the input. Each input can be used
as a normal input or as a MAC or Chroma input (with external Resistor Bridge). All the switching
possibilities are changed through the BUS. Driving 75ohm load needs an external resistor. It is possible
to have the same input connected to several outputs.

5.MULTI STANDARD SOUND PROCESSOR

The MSP34x1G family of single-chip Multi-standard Sound Processors covers the sound processing of
all analog TV -Standards worldwide, as well as the NICAM digital sound standards. The full TV sound
processing, starting with analog sound IF signal-in, down to processed analog AF-out, is performed on
a single chip. Signal conforming to the standard by the Broadcast Television Systems Committee
(BTSC).
The DBX noise reduction, or alternatively, MICRONAS Noise Reduction (MNR) is performed alignment
free. Other processed standards are the Japanese FM-FM multiplex standard (EIA -J) and the FM
Stereo Radio standard.

6.SOUND OUTPUT STAGE WITH TDA7480L

The TDA7480L is an audio class-D amplifier assembled in Power DIP package specially designed for
high efficiency applications mainly for TV and Home Stereo sets.
Mute stand-by function of the audio amplifier can be described as the following; the pin 12
(MUTE/STAND-BY) controls the amplifier status by two different thresholds, referred to ground. When
Vpin 12 voltage is lower than 0.7V the amplifier is in Stand-by mode and the final stage generators are
off. When Vpin 12 is higher than 4V, the amplifier is in play mode.
The TDA7480L is a 10W+10W stereo sound amplifier with mute/stand-by facility. MUTE control signal
coming from microcontroller (when it is at high level) activates the mute function. IC is muted when
mute pin is at low level (pin12). MUTE pin can also be activated via an external pop-noise circuitry in
order to eliminate pop noise when TV is turned off. Just after the TV is turned off, this circuit switches
the IC to stand-by mode by pulling the mute pin voltage to ground.

7.VERTICAL OUTPUT STAGE WITH TDA8177F

The IC TDA8177F is the vertical deflection booster circuit. Two supply voltages, +12V and -12V are
needed to scan the inputs VERT+ and VERT-, respectively. And a third supply voltage, +60V for the
flyback limiting are needed. The vertical deflection coil is connected in series between the output and
feedback to the input.
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