Technik und Service
Seite: 44
Technology and Service
Page: 44
mecablitz 44 MZ-2 / 44 AF-3
ENGLISH
In order to activate the AF measuring beam in the mecablitz, the camera momentarily increases the voltage
on contact SK2 to about 3.1 V. This voltage is sufficient to overcome the thresholds of the two diodes D403
and D406 and causes Tr407 to conduct. The base of Tr310 is connected to ground via R4027 and Tr407.
Tr310 conducts and the LED D001 for the AF measuring beam lights. Tr311 and R322 limit the current
through D001 to about 150 mA.
Synchronisation and TTL pulse:
The mecablitz can be synchronised with either the first or the second shutter curtain (REAR), as desired. This is
selected in the menu of the mecablitz. The data bus of the mecablitz transmits the selected synch mode to the
camera, which then adjusts the control signals on contact SK4 accordingly.
1
st
curtain synchronisation:
For synchronisation with the first shutter curtain, the mecablitz is triggered at the beginning of the camera
exposure time (SYN time). During data-bus traffic, the HIGH level on SK4 (CLOCK) is about 4.7 V and the
LOW level is about 2.2 V. For synchronisation with the first curtain, the camera momentarily switches the
voltage on SK4 to 0 V just before the SYN time. Tr414, which conducts during normal data-bus traffic, cuts off.
From this, the µC IC401 detects at pin 35 (SK4_GND) that the SYN time will follow within a short time. The
mecablitz is triggered with the negative-going edge of the signal on the SYN contact. When the flash exposure
is correct, the camera switches the voltage on the SK4 contact back to HIGH. This positive-going edge is the
TTL pulse which initiates the TTL termination of the flash.
2
nd
curtain synchronisation(REAR):
For synchronisation with the second shutter curtain, the mecablitz may be fired only at the end of the exposure
time. In other words, it may not be fired at the SYN time. The voltage on contact SK4 is evaluated in order to
detect the correct firing time. In contrast to 1
st
curtain synchronisation, the voltage on contact SK4 is not
switched to 0 V before the SYN time, but at the end of the exposure time. The signal is again evaluated with
Tr414 (see above). The negative-going edge of the voltage on SK4 is the signal to trigger the flash. Just as for
1
st
curtain synchronisation, the flash is terminated by the next positive-going edge of the voltage on SK4 (TTL
pulse) if the exposure was correct.
TTL pulse:
In TTL flash mode, the flash is switched off by the TTL pulse received from the camera via special contact SK4.
The TTL pulse (LOW-HIGH transition) on SK4 is detected by comparator IC403B and switches off the gate
logic of the IGBT Tr401, thus switching off the flash.
Wake-up by the camera:
If the mecablitz has been switched to standby mode by its "Auto-Off" function, it can be switched on again by
lightly touching the camera's shutter release button.
