Canon SPEEDLITE 540EZ Service Manual page 45

Part 2: Technical Information
4.9 Charge Inhibit
* In order to prevent malfunction due to a sudden drop in battery voltage caused by an
excessive load being placed on the battery during operation of the zoom motor and
lighting of the AF-LED, charging of the main flash capacitor (C15) is temporarily
inhibited by the following procedure.
(3) When the above High signals are input to RQ10, RQ10 and Q20 turn ON.
SCR1
RQ8
Figure 2-14 Circuit 9
2-23