Technik und Service
Seite: 48
Technology and Service
Page: 48
mecablitz 44 MZ-2 / 44 AF-3
ENGLISH
Activation of the AF measuring beam:
In order to activate the AF measuring beam in the mecablitz, the camera momentarily switches SK1 to ground.
Tr412 thus no longer receives a base voltage and cuts off. The collector of Tr412 switches to HIGH and this
drives the base of Tr423 via R4076. Tr423 conducts and connects pin 52 (via D414) and pin 35 of the µC
IC401 to LOW. The µC recognises this as the command to activate the AF measuring beam and switches pin
33 (REDL_OUT) to HIGH. This drives the base of Tr407 via R4029 and Tr407 conducts. The base of Tr310 is
connected via R4027 and Tr407 to ground. Tr310 conducts and the LED D001 for the AF measuring beam
lights. Tr311 and R322 limit the current through D001 to about 150 mA.
1
st
curtain synchronisation:
The mecablitz can be synchronised with either the first or the second shutter curtain (REAR), as desired. On bus
cameras, the selection is made in the menu of the mecablitz and the camera is informed via the data bus. On
non-bus cameras, the selection is made on the camera and the mecablitz is not informed of the
synchronisation mode. The flash is triggered by the camera via the SYN contact and SK1 in accordance with
the selected synch mode.
If synchronisation with the first curtain is selected, the mecablitz is fired at the beginning of the exposure time,
i.e. at the SYN time. SK1 switches to HIGH some time before the SYN time.
2
nd
curtain synchronisation (REAR):
If synchronisation with the second shutter curtain (REAR) is selected, the mecablitz is fired at the end of the
exposure time. For this, the camera switches the voltage on SK1 to LOW before SYN time. This is followed by
the SYN time, but the flash is not triggered. At the end of the exposure time, the camera switches SK1 to
HIGH. This is the firing time for the flash, so that it is synchronised with the second curtain.
TTL pulse:
The light output is controlled by the TTL pulse from the camera. The TTL pulse is the first negative-going
(HIGH-LOW) edge of the signal on SK2 after the flash has been fired (SYN). In TTL mode, the light output is
controlled via special contact SK2. The negative-going edge of the signal on SK2 is the TTL pulse, and this
switches off the IGBT Tr401.
At the SYN time, the level on SK2 is HIGH. The base of Tr414 is driven via R4041 and R4042 and Tr414
conducts. Pin 13 of IC406D has LOW level. The TTL gate at pin 34 (TTL_GATE) of IC401 is still closed at this
time and is thus also LOW. Pin 11 of IC406D (= pin 8 of IC406C) is thus HIGH.
To fire a flash, the camera switches the SYN contact to ground. The base of Tr416 receives a drive signal via
D413 and R4060. Tr416 conducts and thus drives the base of Tr415. Tr415 conducts and connects pin 52 of
the µC IC401 to ground. In contrast to the activation of the AF measuring beam, pin 35 remains HIGH. The
µC recognises the command to fire a flash and switches pin 53 (IGBT-DRIVE) to HIGH.
Since both NAND inputs (pins 8 and 9) of IC406C are now HIGH, the output of this gate (pin 10) is LOW.
This signal is inverted in the following IC406B and the output of the gate logic (pin 4 of IC406B) switches to
HIGH, causing the IGBT Tr401 to conduct and fire the flash.
A few microseconds after the flash has been fired, the TTL gate at pin 34 (TTL_GATE) of IC401 changes to
HIGH and there is thus a HIGH level at pin 12 of IC406D. Since pin 13 of IC406D is still LOW, the output
level at pin 11 of IC406D does not change and the IGBT Tr401 continues to conduct.
