Automatic Light Output Control; Correct Exposure Confirmation; Syn-Acknowledge - Metz mecablitz 44 MZ-2 Servicehandbuch

Technik und Service Seite: 42
Technology and Service Page: 42
mecablitz 44 MZ-2 / 44 AF-3
ENGLISH

6.3. Automatic light output control:

The light-output control circuit is active only in automatic flash mode A of the mecablitz. The light is measured
only during the actual output of a flash by the mecablitz. The actual light output is compared with the required
value by the comparator circuit IC404A.
Depending on the selected aperture and the selected ISO value, the integration RC circuits are connected to
ground via R4063, R4064, R4065 and via Tr421 and Tr422 and are thus activated. For this, the appropriate
Pins 35 (LIRE C1), 56 (LIRE C2) and 65 (LIRE C3) of the µC IC401 are switched to HIGH.
As long as no flash is triggered, Pin 77 (DISCHARGE) of IC401 is set to HIGH. This connects R4062 to ground
via Tr421 and ensures that the integration capacitors of the light-output control circuit remain discharged.
When a current flows through the flash tube, the µC IC401 receives the SYN-Acknowledge signal at Pin 38
(SYNACKN IN) and immediately switches Pin 77 (DISCHARGE) to LOW. R4062 is disconnected from ground
and the integration capacitors of the light-output control circuit can start to charge via the photodiode D002
(measuring cell for automatic mode) and resistor R4090. The voltage on the integration capacitors is
connected as the actual value to Pin 2 of IC404A (comparator), where it is compared with the required-value
voltage at Pin 3. When the actual value exceeds the required value (sufficient light has been emitted), the
comparator IC404A switches its output at Pin 1 (A-CUTOFF) from HIGH to LOW and the gate logic in IC406
switches its output from HIGH to LOW, cutting off the IGBT Tr401. The flash is thus terminated.

6.4. Correct exposure confirmation:

If sufficient light is emitted in automatic flash mode, the comparator of the light-output control circuit in
IC404A switches its output at Pin 1 (A-CUTOFF) to LOW, causing Tr430 to cut off. The level at the collector of
Tr430, and thus also at Pin 42 (OK-IN) of the µC IC401, changes from LOW to HIGH. The µC IC401
recognises from this that sufficient light has been emitted and activates the OK indicator in the LC display. The
µC IC401 also switches Pin 77 (DISCHARGE) from LOW to HIGH to discharge the integration capacitors
immediately after output of the flash.
If sufficient light is emitted in TTL flash mode, the SCA adapter briefly sends a HIGH level on contact SCA 7.
This drives the base of Tr416 via R4049 and Tr416 conducts. The level at the collector of Tr416 (TTLOFF)
changes from HIGH to LOW, causing Tr431 to conduct. The level at the collector of Tr431, and thus also at
Pin 42 (OK-IN) of the µC IC401, changes from LOW to HIGH. The µC IC401 recognises from this that
sufficient light has been emitted and activates the OK indicator in the LC display. In order to ensure that this
circuit is active only in TTL flash mode, the emitter of Tr431 is connected to Pin 37 (TTL-GATE) of IC401, which
carries a HIGH level only when the TTL gate is open.

6.5. SYN-Acknowledge:

The function of the SYN-Acknowledge circuit around Tr427 is described in Section 8 "Minolta Functions".
However, you should note that component numbers differ from those on printed circuit board B of the 44 MZ-
2! See also the related circuit diagrams!