Notice in Fig. 64 that the memory-
capacitor voltage provides the base bias
fo r transistor #1 inside IC1. The transistor
bias determines how fast the timing
capacitor C3 can charge. However, the
tim ing capacitor can't start charging until
the trigger switch S4 opens. As long as
S4 remains closed, it keeps the C3 com
parator switched low. In turn, the com
parator keeps transistor #2 turned off.
Then, as the opening blade starts to
move, it opens the trigger switch. The C3
comparator now switches high and turns
on transistor #2, Fig. 64. As a result, cur
rent flow s from ground, through tran
sistor #2, and through transistor #1 to
charge the timing capacitor C3.
The higher the memorized reference
voltage, the faster the timing capacitor
will charge. A higher reference voltage
provides a larger base drive to transistor
#1, Fig. 64. Transistor #1 then conducts
more current.
During the C3 charging cycle, current
flow s through the closing-blade elec
tromagnet M3, Fig. 64. Right now, the
output of the M3 comparator remains at
OV. The electromagnet then has a 3V dif
ference in potential. Since current flows
through the coil, the M3 electromagnet
holds the closing blade to keep the shut
ter open.
Then, when the timing capacitor
reaches a high enough voltage, it triggers
the M3 comparator. As a result, the com
parator switches states — its output goes
to 3V. Now there's no difference in
potential across the electromagnet. So
the electromagnet releases its armature
and frees the closing blade.
OPERATION IN THE M MODE
In the M mode, the shutter speed still
depends on the charge across the
memory capacitor. However, the shutter-
speed setting (the resistance of RTV)
determines the memory-capacitor volt
age. A t M, switch S9 moves from the
"A S " position to the "M " position. Fig. 63.
Switch S9 now connects RTV to pin 20
of IC1, Fig. 63. As you set faster shutter
speeds, the voltage at pin 20 goes more
positive. The voltage at pin 19 also goes
more positive at the faster speed settings.
As the voltage at pin 19 goes more
positive, the voltage across the memory
capacitor increases. The remaining opera
tion matches that we described for
autom atic operation.
Increasing the
voltage across the memory capacitor pro
vides a larger base drive for transistor #1,
Fig. 64. The timing capacitor then
charges more quickly.
You can then check the shutter-speed
resistor RTV by measuring the voltage to
pin 20 of IC1 in the M mode. Again, the
voltage should go more positive as you
set faster shutter speeds. A t the X, B, and
0 settings, though, you should measure
OV at pin 20.
W hat if you measure OV at the other
settings? There's evidently an open in the
shutter-speed resistors. Most likely, you'll
simply find poor contact between the
brush at the bottom of the speed selector,
Fig. 55, and the RTV resistance band.
You can then remove the speed selector
(a procedure we'll later describe) to im
prove the brush contact and clean the
surfaces of RTV.
Here's another possiblity — the shutter
works fine throughout part of the speed
range yet hangs open during the rest of
the speed range. For example, you may
find that the shutter works properly at the
speeds of 1 second through 1/60 second.
But it hangs open at the speeds of 1/125
second through 1/1000 second.
The problem could indicate a break in
the RTV resistance band. But you may
find that the RTV resistor board has sim
ply shifted out of position. As a result, the
speed-selector brush rides o ff the
resistance band. Try shifting the position
of the RTV resistor board after loosening
its three screws, Fig. 55.
PIN VOLTAGES, IC1
O nce y o u 'r e fa m ilia r w ith th e
schematic, you can perform much of the
troubleshooting at the pins of IC1, Fig.
65. Fig. 65 shows the pin voltages for IC1
w ith the metering switch S5 closed.
Normally, the voltage at pin 1, will be a lit
tle less than 3V; it's the battery voltage
minus the drop across T1, Fig. 63.
Earlier, we indicated that you can
check the RTV resistor at pin 20, Fig. 65.
In the M mode, the voltage should go
from around 1.1V at the 1-second setting
to around 1.36V at the 1/1000-second
setting. You should measure 0V at the 0,
X, and B settings. If you measure 0V at
any of the other settings, suspect poor
contact in the shutter-speed resistor.
FRO NT OF C A M E R A
1
20
1.1 — 1.36V (M M O D E )
3 V |
1.1 — 1.4V (A . S M O D E S )
2
19
3
18
4
17
5
16
6
15
7
14
8
13
9
12
10
11
0.45 —0.8V (
] 0.5 —0.7V
0.2V [ ~
| 1.33—1.36V
0.7V f
] 1.1 — 1.2V
ον
Γ
1
I
ov
1 . 0 6 - 1 . 25V f
.] 1.9 — 2.4V
1.13V
I
J
OV
( 0 .1 6 - 0 .1 /V LOWER
T H A N PIM If)
l
2 .8 —2.95V
0V U N T IL RELEASE
kX P O SU R E )
0.5 —0.7V
t
J
1.1 — 1.36V (S M O D F I
(M O R E PO S ITIVE
1 . 0 - 1 . 1V (A . M M O D E S )
A S C2 V O LT A G E
INC R E ASE S)
--
Figure 65
Voltages w ith S5 dosed, shutter cocked
Figure 66
