Canon 40D - EOS 40D DSLR, Service Manual

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Technical Information
15
４）Electrical components
The major circuit boards are as follows: 1. Main board (digital control circuit and camera
control circuit), 2. Bottom board (flash circuit and actuator drive circuit), and 3. Power
circuit board. These boards efficiently integrate various control circuits (Fig. 031). There
are also 23 flexible boards outfitted with the sensor, switches, etc.
⑴Main board
Highly integrated, 10-layer board containing the digital control circuit and camera
control circuit. It includes the following: Image signal-processing circuit consisting of ICs
such as the A/D IC which converts the CMOS sensor output to a digital signal and the TG
(Timing Generator) which generates the CMOS sensor's drive pulse, the digital image-
processing circuit which has DIGIC III, the memory circuit which has DDR-SDRAM as the
buffer memory, and the TFT liquid-crystal control circuit. The USB terminal, video OUT
terminal, and extension system terminal are also on this board.
This board also has the following: Main CPU which controls various sensors and
mechanical parts for camera operations, viewfinder display drive control circuit, and
EEPROM memory to store saved data such as adjustment data (AE, AF, etc.)
⑵Bottom board
Highly integrated, 4-layer board containing the flash circuit and actuator drive circuit.
It includes the flash circuit which controls the built-in flash's recycling and firing and the
external Speedlite control circuit.
It also includes the following: Two-motor control circuit which drives the mirror and
shutter-driving actuator, lens power supply control circuit, Self Cleaning Sensor Unit's
actuator drive control circuit.
⑶Power circuit board
This has the power circuit which generates and supplies the voltage required by the
camera's circuits.
Main board
Bottom board
Power supply
board
Fig. 031 Major hard boards