Chapter 4: Circuit Operation Theory - BenQ PB8250 Service Manual

Chapter 4: Circuit Operation Theory

PB8250 DMD projector being using the XGA DMD Engine made by BENQ, it included
front end circuitry that digitizes and scaling processes for the input analog VGA and TV signals. As
shown, in figure below the front end circuitry consists of :
1. Frond end Circuitry
1.1 Power supply module include PFC and DC/DC portion. DC/DC portion provide 12V, 5V and
2,5V for whole system.
PFC
IGNITOR
POWER SUPPLY
Module
AC IN
DC to DC
EMI Filter
1.2 Pixelworks scaler(PW166
whole system operation and with crucial role of this system.(Include fan speed, inter-lock SW,....)
A/D-decoder(AD9882) are used for decoding VGA analog signal to digital signal(RGB 888)
which provide 24 bit true color resolution and Digital Visual Interface (DVI) receiver . It can
accept SOG(sync on green) and composite signal for PC input. It also support YpbPr.
1.3 The video decoder that process TV video signal input. The TV video signal support both of
composite and S-video input and output YUV format to scaler processor. The basic
following.
12V
Lamp Fan1
Lamp Power
Lamp Fan
12V,5V,2.5V
) with x86 CPU, OSD and SDRAM is used for system control. It control
Power Fan
For System
61
block as