Minolta XE - 12. Explanation of Circuits; A. Control Circuit

12. Explanation of Circuits
A. Control Circuit
When
the
main
switch
(Si)
is
turned
on,
the
addition
and
the
indication
circuits
will
work,
and
the
meter’s
pointer
will
swing.
A
constant
current
of
254A
usually
flows
through
the
addition
circuit.
The
bridge
circuit
comprising
the
light
receiving
element
(CdS)
and
resistors
(Ro,
Roe,
Rs,
Rs’
and
Ri)
obtains
an
output
of
18mV
per
Ev.
The
current
of
254A
will
be
adjusted
by
Ri,
the
common
terminal
of
the
CdS
(on
the
lens
side)
will
be
opened
(removed),
and
a
decrease
in
the
voltage
of
Roz
will
be
measured.
That
is
to
say:
25(A)X15.
5(KM)=
25
x
10-®
x
15.5
x
10°
=
387.510
°
=
387
.5mV
The
constant
current
of
25mA
will
pass
through
Tru
via
the
CdS
circuit
and
join
another
constant
current
of
8A
coming
from
R2.
Then
the
two
(25uA
+8yA=33
A)
will
flow
to
the
earth
via
ASA
(Rsv)
and
the
diaphragm
resistor
(Rav).
At
a
resistance
value
of
about
540M
per
Ev,
the
slide
resistors
(Rsv+Rav)
will
become:
5409
x
334A
—540x
33
x
10-*
+
18X10
*(V)
+=
18mV
Then
they
will
transmit
information
on
the
ASA
and
the
aperture
to
the
addition
circuit.
Rav
and
Rsv
cause
a
problem
because
of
a
difference
in
their
properties.
For
example,
the
8-step
conversion
volume
of
Rav
will
be:540
N)x
8x
33(u~A)
=540x
8
x
33
x
107°
=
143
x
10
*(v)
=143(mV)
However,the
7%
difference
in
its
property
will
cause
an
error:
143mV
X
0.07
+
10(mV)
10/182:0.5Ev.
Therefore,
a
constant
current
of
8A
will
be
corrected
by
Rez
and
the
output
will
be
stabilized.
The
output
obtained
in
the
addition
circuit
can
be
obtained
from
the
midcontact
point
between
Ri
and
Rs
in
the
CdS
circuit.
The
memory
switches
(Sz
and
S2),
when
turned
on,
will
charge
the
memory
condenser
(Ci)
with
the
output
of
the
addition
circuit.
When
the
shutter
is
released,
each
switch
will
work
as
shown
in
Table
1.
When
S?
is
turned
off,
Ci
will
be
separated
from
the
addition
circuit
and
memorize
the
given
information.
When
the
shutter
button
is
further
pressed,
the
mirror
moving
system
will
work,
Ss
will
be
turned
on
to
activate
the
first
switching,
the
delay
and
the
second
switching
circuits,
the
magnet
will
be
energized,
and
the
second
curtain
will
be
suspended.
Table- 1
Film advance completed —p—~ 5, ON, S: ON, 5S; ON, Si, OFF
5, ON, S. OFF, 5; OFF
Ri
Release starts —
—=—}- Ri Constant current
‘
Memory
—P—S:
OFF
Mirror operation starts =
Magnet ON —p— 5S, ON
p—S' ON
h—S;, S; OFF
pS, ON
First curtain runs
+
Second curtain runs
Mirror down =
Trill — S, ON, 5; ON
+ — S, OFF
eS, OFF
Shutter button returns ——— S, ON
Le
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Film advance completed “= --n-- 02 -t mer tnt nen nn