Remote Control Reception Circuit (For Slave Units) - Canon 580EXII Service Manual

.0 Remote Control Reception Circuit (For Slave Units)

(1) When the Speedlite 580EX II is set as a slave unit, IC107S pin 95 is set to "L" and
RQ105S is turned on to supply VCC to the remote control reception circuit.
(2) When supplied with VCC, Q25 turns on. When light hits sensor element PD8, it passes
through RQ25 and an optical current corresponding to the light amount received goes to
PD8. (Constant light)
(3) At this time, the light pulse transmitted from the master flash reduces the current
flowing to PD8. That is, the current which flowed from anode to cathode at PD8 and was
applied as bias to the base of Q27 through C47, causing the collector of Q27 to conduct
and turn on through R135 through C49 turning Q29 OFF. Then, the current of R136
turns on Q30 through C50, turns off RQ15, and sets pin 1 of IC19 to "H". The minimum
pulses at C88/R205 is amplified, and input into pin 101 of IC107S.
(4) Based on this signal, IC107S analyze wireless communication and controls flash mode
output in accordance with the commands from the master unit.
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