JVC 250, Service Manual

Page: 126 / 190

Chapter 5---Electronics
Model 250 Service Manual 5-71
Quad Standard Decoder VIC - Inputs
Comp - input for Composite image signal includes sync pulses (.07-1 Vpp)
Yin - input for Luminance or brightness information of S-image (0.7-1 Vpp)
Cin - input for Chrominance or color information of S-image (0.3-0.6 Vpp)
+15 V - power for analog circuitry
+5.1 V - power for digital circuitry
IIC CLK - IIC clock line
IIC DATA - IIC data line
IIC SINT - IIC interrupt line
Quad Standard Decoder VIC - Outputs
RED_VIC - red image to Video Processor PCB (0.7-1.0 Vpp).
GRN_VIC - green image to signal Video Processor PCB (0.7-1.0 Vpp).
BLU_VIC - blue image to Video Processor PCB (0.7-1.0 Vpp).
SYNC - composite horizontal and vertical sync to Video Processor PCB.
/SEL_VIC - VIC select line to Video Processor PCB.
Quad Standard Decoder VIC - Operation
The Quad Standard Decoder VIC accepts two source input formats, Composite
and S-image. The Composite format combines the image (red, green, and blue)
signals and the sync pulses (horizontal and vertical) into one signal. The S-image
signal has two separate inputs, one contains the color information (Cin), and the
other input contains the black and white information (Yin). The sync pulses are
combined with the Yin. Both the Composite and S-image formats may be in a
variety of different signal standards such as NTSC (U.S.), PAL (European),
SECAM, or 4.43 NTSC. The VIC accepts all of these standards. The Quad
Standard Decoder VIC converts Composite and S-image to the RGBHV format.
The selection of the VIC and inputs is controlled by the System Controller Board
via the IIC serial bus interface. An operator selects the VIC and input in the
Channels Menu (see section 4-6 in the User’s Guide).
The Quad Standard Decoder VIC strips the sync pulses that are combined with
the black and white information (Yin) and sends them to the Video Processor
PCB as a composite sync signal. The Video Processor PCB separates the
composite sync signal and sends it to the Raster Timing Generator PCB.
The Quad Standard Decoder VIC also does signal processing with the Tint, Color,
and Sharpness options in the Picture Menu. The Tint control adjusts the tint of the
colors displayed. Facial tones will vary from slightly green at zero to slightly red
at 255. The Color control adjusts the amount of color saturation or color intensity.
Colors will be almost grayscale at zero and very saturated at 255. The Sharpness
control adjusts the high frequency peaking of the black and white details.
The Quad Standard Decoder VIC has two LEDs. The Composite LED illuminates
green when the Composite input is selected. The S-image LED illuminates green