Figure 100
simulates the camera's timing circuit at
the 1/1000-second setting. There are
several ways you can build such a timing
circuit. Fig. 100 illustrates one method.
You should have no trouble in obtaining
the components from any electronics
supplier.
A lthough you could build the power
supply into the test box, we've designed
the circuit of Fig. 100 to be used w ith a
separate 3V DC power supply. Notice
that the magnet lead connects to the col
lector of a switching transistor. A com
parator controls the signal at the tran
sistor base. W hen the output of the com
parator goes high, the transistor switches
on. The transistor then conducts current
through the shutter's electromagnet.
The trigger switch of the shutter con
nects to the timing capacitor of the timing
circuit. W ith the shutter cocked, the closed
trigger switch shorts the timing capacitor to
ground. Then, when you release the shut
ter, the trigger switch opens and allows the
timing capacitor to start charging.
W hen the timing capacitor reaches the
reference voltage, the comparator sw it
ches states — the output goes low to
shut o ff the transistor. In turn, the tran
sistor shuts o ff the current through the
shutter's electromagnet. In Fig. 100,
w e've provided a variable-resistor adjust
ment to establish the reference voltage at
the noninverting input of the comparator.
Use the variable resistor to adjust the tim
ing circuit for 1/1000 second.
W e've also provided a second speed in
Fig. 100. As mentioned earlier, the slower
shutter-speed setting serves as an opera
tional check. You may wish to set the
second speed fo r 1/100 second, the full-
aperture speed. That way, you can also
use the test box fo r checking X-sync
operation.
Rather than the comparator IC, you
may prefer to use a two-transistor switch
as shown in the inset, Fig. 100. Connect
the base of the second transistor to the
timing capacitor. By using a variable
resistor to control the capacitor-charge
time, you can adjust the test circuit for
1/1000 second.
ADJUSTING THE RELEASE SWITCH
AND THE METERING SWITCH
There's another reason for removing
the shutter — to reach the release switch
S3 and the metering switch S5, Fig. 101.
Earlier, we described how you can check
the tw o switches w itho u t disassembly.
However, if you pinpoint the problem to
one of the switches, lift aside the shutter
to make the repair (you d o n 't have to
disconnect the shutter wires to adjust and
clean the switches).
A sliding brush contact. Fig. 101,
closes both switches as you depress the
release slide. The brush first connects the
green-wire land to ground, thereby clos
Figure 101
SWITCH
