Technik und Service
Seite: 46
Technology and Service
Page: 46
mecablitz 44 MZ-2 / 44 AF-3
ENGLISH
This HIGH level is generated by µC IC401 as the result of a HIGH level at Pin 50 (ENFORCED_LOW) or a
HIGH signal at Pin 4 of IC403 (reset input of the D-flip-flop).
In order to switch SK1 back to HIGH, Tr409 is cut off by a LOW level at Pin 2 of IC403 (NOT-output of the D-
FF). This LOW level is generated by µC IC401 as the result of a HIGH level at Pin 36 (ENFORCED_HIGH) or a
HIGH signal at Pin 6 of IC403 (set input of the D-flip-flop).
On various Minolta cameras (such as the Dynax 800si, 7, 9), it is possible to select second curtain
synchronisation (REAR) on the camera. This has no effect on the sequence of signals on the camera interface.
SYN acknowledge:
Once the mecablitz has received the ignition command for the flash from the manual release "TEST" (S402) or
from the hot shoe contact (SYN) of the mounting foot, and has passed this on to the ignition circuit, there is a
certain delay before the current actually flows through the flash tube. However, for certain processes in the µC
(such as for ADI flash control), it is necessary to know precisely when the current starts (or started) to flow
through the flash tube.
The base of transistors Tr412 is connected directly to ground, while the emitter of Tr412 is connected via
R4076 and R4000 (20 mOhm measuring resistor) to ground. Resistor R4000 is also part of the flash-current
circuit at the negative pole of the flash capacitor C001.
When a flash is triggered and the current starts to flow through the flash tube, a negative voltage (with respect
to ground) is generated across R4000 and thus at the negative pole of the flash capacitor C001. This negative
voltage passes through the RC circuit with R4076 and C415 to the emitter of Tr412. The base of Tr412 is now
more positive (since it is at ground potential) than its emitter, Transistor Tr412 therefore conducts and Pin 65
(SYN-ACKNOWLEDGE IN) of the µC is switched to LOW. By detecting this change, µC IC401 recognises that
a current has started to flow through the flash tube (= SYN - Acknowledge).
Preflash metering and ADI flash control:
The mecablitz supports both the preflash metering and ADI (Advanced Distance Integration) flash control
functions of the Minolta digital cameras Dimage 5, 7, 7i, etc. Both of these functions are modern variants of
the well-known TTL flash control. The two functions differ only at the camera level; the processing in the
flashgun is identical for both.
For these two flash methods, a precisely defined measuring preflash is triggered before the actual main flash.
The camera measures the light reflected by subject and calculates the necessary partial light output for the
main flash. This value is sent via the data bus to the flashgun and the main flash is then triggered with the
partial light output specified by the camera. There is no additional TTL control of the flash.
The main flash is triggered by the HIGH-LOW transition on the SYN contact. The duration of the main flash,
i.e. the required partial light output, is determined by the HIGH time at Pin 53 (IGBT-DRIVE) of IC401, which
depends on the value sent by the camera via the data bus to the flashgun after the measuring preflash.
TTL pulse:
In TTL mode, the light output is controlled by the TTL pulse from the camera. This is the first positive-going
edge (LOW-HIGH) on SK2 after a flash has been triggered (SYN). The activation of the IGBT TR401 by a
HIGH signal at Pin 4 of IC406B is terminated by the TTL pulse and the flash is switched off.
