Metz mecablitz 44 MZ-2 Servicehandbuch Seite 39

Technik und Service Seite: 39
Technology and Service Page: 39
mecablitz 44 MZ-2 / 44 AF-3
ENGLISH
SCA 5 - SCA 300 supply voltage:
Contact SCA 5 carries the supply voltage for the adapters of the SCA 300 system. Generally, this voltage may
lie within the range 4 V to 9 V during normal operation. After a flash has been fired, it may drop to 2 V, but
not less. This voltage is taken from the battery voltage and is protected against overloads by R301 and fuse
Si301. Contact SCA 5 is not used by adapters of the SCA 3002 system.
SCA 6 - Flash mode:
Adapters of the SCA 300 system evaluate the signal on contact SCA 6 of the mecablitz in order to determine
which flash mode (TTL, automatic, manual) has been selected. The mecablitz 44 MZ-2 no longer supports the
aperture control of older Canon cameras (such as the Canon T70), which means that the related resistor
network on SCA 6 is no longer needed. Instead of this, a resistor with a value of 8.2 kOhm (R4028) is
permanently connected to contact SCA 6. This resistance value (previously 8.66 kOhm) stands for TTL flash
mode and is basically needed only for some older cameras (such as the Canon T90 with SCA 311). Adapters
of the SCA 3002 system receive the information about the flash mode selected on the mecablitz via the data
bus (SCA 11 and SCA 12).
Regardless of the selected flash mode (TTL, automatic, manual), the resistor R4028 remains connected to
contact SCA 6.
SCA 7 - TTL flash control:
In TTL flash mode, the mecablitz receives a command via contact SCA 7 to terminate the flash when sufficient
light has been emitted. For this, the SCA adapter briefly sends a HIGH level on SCA 7, causing Tr416 to
conduct. The level at the collector of Tr416 (TTLOFF) changes from HIGH to LOW and this signal, with the aid
of the gate logic (IC406), causes IGBT Tr401 to be cut off, thus terminating the flash.
SCA 8 - Flash readiness:
In order to detect whether the flashgun is ready to fire a flash, the voltage on the flash capacitor C001 is
monitored with the aid of the voltage divider consisting of R4010 and R4011. The output from this voltage
divider is connected to Pin 47 (U MAIN CAP IN) of the µC IC401. This pin is the input to an AD converter
which measures and evaluates the voltage on the flash capacitor. If the voltage on the flash capacitor is
>280 V, a voltage of >3.4 V is present at Pin 47. The µC recognises from this that the flash-capacitor voltage
is sufficient for flash operation and therefore signals flash readiness as follows:
The µC IC401 switches Pin 66 (BB_OUT) to LOW. The LED D408 then lights to indicate the flash-ready
condition on the mecablitz.
The LOW level at Pin 66 of IC401 causes transistor Tr410 to conduct and this activates the base of Tr409 via
R4035, causing Tr409 to conduct. This results in a LOW level at contact SCA 8. An adapter of the SCA 300
system recognises from this that the mecablitz is ready for firing. If the mecablitz is used with an adapter of the
SCA 3002 system, the flash-ready state is simultaneously signalled to the adapter via the data bus (SCA 11
and SCA 12).