NEC PlasmaSync PX-42VM1G, Service Manual

Page: 106 / 172

6-1
CIRCUIT DESCRIPTION
I. MAIN PWB Circuit Operation
1. Video signal processor block
In the MAIN PWB, various video signals converted into analog RGB signals at the VIDEO PWB are further
converted into digital signals, and various signal processing for enlargement, contraction, etc., is carried out
there. The signal output is then sent to the plasma display module.
There is difference in the signal flow and IC processing between various analog signal inputs and digital
signal inputs (RGB3). Also in analog signal inputs of various kinds, some difference lies between the video
signal, DVD, and video RGB inputs and others.
(1) Signal flow for the RGB input of video signal, DVD, and VIDEO
LPF
(8MHz)
RGB
→
422
IC7503
AD
Converter
IC6502
I-P
Convert
IC7506
ϒ
Process
On screen
IC9004
Screen Size
IC8501
The RGB signal input entered from the MN connector is converted into the digital signal at the AD
converter of IC6502. Since then, the RGB signal is converted into the Y chrominance (422) signal at
IC7503, and fed to IC7506. In IC7506, the horizontal interlace signal at 15kHz is converted into the
progressive signal of 31kHz. In IC8501, the video signals are processed for screen size conversion, such
as for normal size, full size, etc. In IC9004,
γ
processing and gradation processing are carried out for the
digital video signals. In addition, ON-screen signals are also synthesized there. After that, latch process-
ing is carried out in IC9006, IC9007, and IC9008, and the output is sent to the plasma display module
(the AD connector).
(2) Signals in cases other than (1) above
LPF
Auto
Picture
IC8701
AD
Converter
IC6502
Scan
Convert
IC8501
Sharpness &
screen Size
IC7506
ϒ
Process
On screen
IC9004
Signal
Select
IC7503
The RGB signal input entered from the MN connector is converted into the digital signal at the AD
converter of IC6502. In the case of the PC signal, information about the screen position of the input
signal is picked up (auto-picture function) at IC8701 and transmitted to the CPU. In IC8501, scan conver-
sion is conducted to convert the XGA signal into VGA equivalent and screen size change is carried out
for the zoom and other functions. In IC7503, signal changeover is performed between the video signal
from the AD converter and that from IC8501. In IC7506, profile emphasis and noise reduction processing
are carried out. If the input signal is for SXGA, processing for enlargement and contraction is carried out.
In IC9004,
γ
processing and gradation processing are carried out for the digital video signals. In addition,
ON-screen signals are also synthesized there. After that, latch processing is carried out in IC9006, IC9007,
and IC9008, and the output is sent to the plasma display module (the AD connector).