TROUBLESHOOTING THE
ELECTROMAGNETIC RELEASE
SYSTEM
If the shutter fails to release elec-
tromagnetically, you might first suspect
switch S1. But you can also check the
other possibilities after removing the bo t
tom plate. The mirror-release magnet M1
may have an open coil, the mirror-release
capacitor C6 may be open or shorted,
transistor T6 may be open, or T6 may not
be getting the release signal from the
comparator.
It's also possible that the problem is
mechanical rather than electronic. To
check the mechanical release action, cock
the shutter and push the M1 armature.
Fig. 11, toward the fro n t of the camera.
The mirror should release. If it does, you
know the mechanical release is working
properly. And the problem must be w ith
the circuit.
Fig. 13 shows the approximate voltages
you should measure across the M1 com
ponents. Notice that the mirror-release
capacitor C6 charges to the full battery
voltage. You should measure the + 3 V at
the positive terminal of C6 regardless of
whether the shutter is cocked or released.
However, before measuring voltages,
you might try a quick shorting test to
simultaneously check both capacitor C6
and the coil of magnet M1. Cock the
shutter. Then bypass transistor T6 by
shorting between its emitter and collec
tor, Fig. 13. The mirror should release.
If your shorting test releases the mirror,
you know that both the combination
magnet M1 and the mirror-release capa
citor C6 are good. You might next try
checking for the release signal at the base
of transistor T6, Fig. 13. W ith o u t de
pressing the release button, you should
measure around 2.5V — the output of the
comparator in the " h ig h " state. If you
measure the full 3V signal, T6 apparently
has a base-to-emitter short. Now depress
the release button. The signal should
drop to around 1.3V.
If the circuit fails to supply the release
signal to the base of T6, you'll have to go
further in the disassembly. There may be
a problem w ith the release switch or w ith
the release circuit. But if the transistor T6
is at fault, you w o n 't have to go any fu r
ther. You can make a final check on T6 by
shorting between the base and the collec
tor, Fig. 13. Your short connects the base
to ground through the coil of M1. If the
transistor is good, the mirror should
release.
Replacing the transistor gives you a
choice in repair procedure. Minolta does
supply the individual components. But
you may prefer to replace the complete
circuit board (circuit base plate B).
Now let's say that the shutter doesn't
release when you short between the emit
ter and collector of T6. Either the com
bination magnet M1 or capacitor C6 could
be at fault. But you might first suspect
the coil of M 1. The red wire connected to
the collector of T6 goes to one side of the
coil; the other side of the coil connects to
ground through a black wire, Fig. 13. To
check the coil, measure the resistance
between the red coil wire and ground.
You should measure a very low resistance
— around 15 ohms. If you measure no
continuity, you know that the combina
tion magnet M1 has an open coil. You'll
then have to remove the front-plate
assembly to replace the combination
magnet.
CHECKING THE DIAPHRAGM-
CONTROL CIRCUIT
You can follow practically the same
troubleshooting procedure to check the
circuit fo r the second combination
magnet — the diaphragm-control magnet
M2. Remember, the diaphragm-control
magnet arrests the diaphragm closure in
the " S " mode. If there's a problem in the
M2 control circuit, the diaphragm always
stops down its full amount.
In Fig. 14, note the similarity between
the diaphragm-control circuit and the
mirror-release circuit. When the dia
phragm reaches the proper f/s to p , the
aperture-control comparator switches on
transistor T13. T13 then supplies the base
current which turns on transistor T5.
Turning on T5 allows the diaphragm-
control capacitor C5 to discharge through
the coil of the diaphragm-control magnet
M2. M2 now repels its armature to arrest
the diaphragm-closing lever.
B LAC K (GROUND)
RED TO
* BATTERY
Figure 13
Figure 14
