JVC AV-2771S Service Manual page 22

AV-2771S |
_@DIGITAL VIDEO PROCESSING CIRCUIT
[ PIP(PICTURE IN PICTURE) PCB Ass'y & PIP INTERFACE PCB Ass'y }
° The normal analog video signal is sent to a circuit that includes ENCODER, DECODER, A/D CONVERTER, MEMORY, D/A
CONVERTER and MEMORY CONTROLLER. Digital processing is performed and picture in picture function produces two
pictures.
The basic circuit composition is the same as the AV-3290S and AV-3590S, expect for only the PIP function. Therefore, only the
differing points are indicated below. Refer to the AV-3590S SERVICE MANUAL (No.50341, issued August 1990) regarding other
sections. :
The circuit block diagram is shown in Fig. A.
eiC011
In event the sub picture is absent, without an input, or noisy, video muting is applied to produce a black screen. The detection
signal(muting signal) is produced by this IC. The function operates by dividing the sub picture video signal and detecting presence
or absence of synchronization signal.
@1C012
If the sub picture signal is absent or without an input, due to the lack of synchronization signal in the sub picture, quivering or
vertical roll can occur in the main picture. This circuit produces a still sub picture even in absence of an input signal. The main
picture signal(synchronization signal) is switched and sent to the sub synchronization input of the memory controller. The circuit
operates by detecting the video muting signal sent from 1C011 when the sub picture signal is absent.
e1C013
In order to produce a completely black picture when the video muting signal from |C011 indicates absence of a sub picture input
signal, the internal switches operate to mute Y, R-Y and B-Y.
10008, ICO09
Clock oscillator for memory controller read-in and write-in. Provided in order to avoid operating error due to weak or deteriorated
input signals.
10004, 1C005
A/D converter and D/A converter. Include built-in multiplexers required during input and output (input : for R-Y and B-Y, output :
for Y).
@1C1821 [MAIN PCB Ass'y]
Normally, if the PIP mode is set while viewing the antenna(TV) input picture, the video input signal appears as the sub picture.
However, if nothing is connected to the video input when setting the PIP mode, the antenna input signal also appears in the sub
picture. This circuit switches and routes the antenna input signal to the video input so that it appears in the sub picture during the
PIP mode.
@1C1861 [MAIN PCB Ass'y]
This circuit normally operates to switch to the TV and video input video signals. During PIP, it operates to interchange(SWAP)
the main and sub pictures and switch to the sub picture input mode.
@/C8251 [PIP INTERFACE PCB Ass'y]
When equipment is connected to S-VIDEO IN, this circuit switches automatically from composite video Y/C signal to separate Y/C
signals via S-VIDEO IN.
Switch states in various modes (MAIN=TV, SUB : VIDEO (composite) input)
: PIP VF PCB ;
MAIN PCB ASS'Y PIP PCB ASS'Y
IC861 icoor | ico1o | ico12 | ico13
PIP operation
SUB picture input
por fv | ve | - |
Normal
(PIP = OFF)
XK T =same as above
22 (No.50577)