3M
Multimedia Projector MP8620
Theory and Diagrams
3M 1999
4-1
4.
Theory and Diagrams
4-1.
Overview
In order to truly understand what is taking place when making advanced projector adjustments, the following
concepts must be introduced and explained. An understanding of these principles increases your efficiency when
making advanced projector adjustments. The diagrams in this section assist you in finding the pin locations,
connectors and wiring during troubleshooting.
4-2.
Theory of Operation
Use the projector circuitry diagrams as a reference when reading the topics in this section.
4-2-1.
Power Supply Circuit
When the main power switch is on and the 110V AC power is supplied, two DC power circuits are energized.
The AC power passes through a filter then on to the ballast where the AC voltage changes to DC voltage and is
split. High voltage DC current is sent to the lamp where it will have six tries to light. Low voltage DC current is
sent to the power unit circuit then to the Micro processor to power the rest of the projector.
4-2-2.
Video Input and AD Conversion
There are two sets of video inputs. Switching between them is done using the input button on the top of the
projector or the Video1/2 button on the remote control.
Signal Board
The video signal passes though the video signal selector then to the comb filter where it is split into the chroma
signal (C). It is then sent to the RGB/video selector and the luminance (Y) signal is sent to the sync selector.
Driver Board
The signal passes through another selector before the AD converter. The analog signal is changed to a digital
signal and passes though the on screen display. The gate array is where a smoothing affect and resizing takes
place. The signal is then changed back to analog and sent to the video amplifier/inversion amplifier. The
luminance signal (Y) information passes through the gate array and timing generator. A PLL circuit generates
the sampling pulse for the AD converter and is dependent upon the detection of vertical and horizontal sync
pulses. The two signals are output though the video amplifier, where the sample/hold and video rotation take
place before each LCD receives the appropriate information.
