Canon SPEEDLITE 540EZ Service Manual page 43

Part 2: Technical Information
4.7 Auto Zoom
(1),
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
When camera's SW1 is turned on, the focal length information is input to the flash
unit (pin No.9 of IC7) on the EFID line from the camera.
IC7 relays this information to pin No.72 of IC8 from pin No.26.
By this, IC8 internally judges whether or not auto zoom is needed.
When the focal length information has been changed, a signal is sent to the LCD
display from IC8, and the new focal length is displayed.
To adjust the flash coverage angle, a High signal (dependent on the zoom direction)
is input from one of pins No. 51 or 52 of IC8.
When this signal is input to either of pins No.4 or No.8 of IC9, pins No.15 and 17 of
IC9 become High and Low, respectively, the motor rotates (changes depending on
the direction of zoom), and the internal flash head unit moves.
This movement status is input to pins No.69 to 72 of IC8 by the zoom detection
switch.
Motor rotation continues until the focal length information from the lens matches
the zoom detection switch information in order to set the correct flash coverage
angle.
Note: During motor rotation, the signal from pin No.14 of IC8 is input to RQ10 in order
to inhibit charging of the main capacitors. (For details, see 4.9 Charge Inhibit.)
* When using bounce flash, the flash coverage angle is automatically set to the 50mm
focal length (controlled by MPU).
¢ Flow of Operation: (1) > (2) > (3) 3 (4) C (5) — (6) > (7)
Charging inhibited
BATT1 GND
cam alee
FEARERNE
IC9
,O LB1634M 10
on
Figure 2-12 Circuit 7
2-21