Canon SPEEDLITE 540EZ Service Manual page 46

Part 2: Technical Information
4.10 Panel Illumination (EL) Lighting
(1) If you press the EL-SW switch on the rear of the control panel, the signal from EL-
SW is input to pin No.70 of IC8.
(2) This repeatedly outputs a pulsed High signal to pin No.16 of IC8.
(approx. 4.6 KHz, output for approx. 8 seconds after operating EL-SW)
(3) When the High signal is input to the base of RQ5, RQ5, Q10 and Q11 turn ON.
(4) When the base of RQ5 goes Low at the rise of the next pulse, RQ5, Q10, and Q11
turn OFF.
(5) By repeating the operations in steps (3) and (4) above, a high-voltage pulse (approx.
70V) raised by T4 is applied to EL1, causing it to light.
Figure 2-15 Circuit 10
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