Metz mecablitz 44 MZ-2 Servicehandbuch Seite 36

Technik und Service Seite: 36
Technology and Service Page: 36
mecablitz 44 MZ-2 / 44 AF-3
ENGLISH
Blanking the entire display:
At IC401, pin 45 (UBAT IN), the voltage divider consisting of R4008 and R4009 monitors the +6 V battery
voltage. If this voltage drops below about 1 V (for example if a flash is triggered when the batteries are almost
exhausted), this is detected at pin 45 of the µC IC401 and the µC then blanks the entire display in the LCD
module. The display is enabled again in the LCD module only when the battery voltage rises to a value of
about 1.2 V.
Blanking the maximum flash range display:
Most cameras inform the mecablitz via the data bus about the selected aperture, the ISO film speed, the focal
length, etc. From these values, the mecablitz calculates, amongst other things, the maximum flash range and
displays this on the LC display. If the flash reflector is moved from its normal position, the maximum flash
range display is suppressed. The fact that the reflector has been moved is signalled by a LOW level at pin 43
of the µC IC401 (GESCHW IN) generated by the switch S401 (VERT GESCHW), which is closed when the
reflector is swivelled vertically. In the normal position of the reflector, S401 is open and the level at pin 43 of
the µC IC401 Pin 43 is HIGH.
LC display illumination:
If the user presses the button "Mode" (S403) or the button "Zoom" (S404), the illumination of the LC display is
switched on. For this purpose, pin 60 (BACKLIGHT O/F OUT) of IC401 is switched to LOW for about 10
seconds. Via R4074, the base of Tr419 then receives a drive signal and the transistor conducts. The collector
current of Tr419 is split between the two LEDs D409 and D410, which illuminate the LC display. The
magnitude of this current is kept constant at about 22 mA with the aid of Tr426 und R4072. Due to the
regulation effect of Tr426 in the base circuit of Tr419, this current is virtually unaffected by the supply voltage
or the operating state of the converter.
AD converters in the µC
The AD (analogue-digital) converters in the µC IC401 are used, for example, to measure the battery voltage
and the flash-capacitor voltage and to determine the zoom position. They receive their supply voltage via a
separate terminal. The +5.0 V supply voltage is connected to pin 39 (AV DD) of the µC IC401. The maximum
voltage which can be measured is determined by the voltage at pin 40 (AV ref), to which the switched supply
voltage +5VG is connected. With the mecablitz switched on, the measuring circuits have a resolution of 256
values in the range 0 V to 5 V.
Motor zoom control
The zoom motor is controlled with the levels at pin 75 (MC1 OUT) and pin 76 (MC2 OUT) of the µC IC401. If
the reflector is not moved, or if it is already in the desired position, both of these pins are HIGH and Tr201 to
Tr206 are cut off. No current flows through the motor. In order to move the reflector towards the 105 mm
position, pin 76 of IC401 is switched to LOW (MZ circuit board, ST201, contact 4, ZOOMH), while pin 75 of
IC401 remains HIGH (MZ circuit board, ST201, contact 3, ZOOML).
Transistors Tr201, Tr202 and Tr205 now conduct, while Tr203, Tr204 and Tr206 remain cut off. A current
flows through Tr202, the zoom motor and Tr205 and the reflector moves backwards. The actual position of
the reflector is detected by the position of the switch S202. In the 28 mm position, S202 is in position 6.