Operation In The M Mode; Pin Voltages, Ic1; Voltages With S5 Closed, Shutter Cocked - Minolta XD-11 Repair Manual

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
timing 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 flows 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
3 V |
0.45 —0.8V (
0.2V [ ~
0.7V f
ον Γ
1 . 0 6 - 1 . 25V f
I
1.13V
(0 .1 6 - 0 .1 /V LOWER
T H A N PIM If)
0V U N T IL RELEASE
t
0.5 —0.7V
(M O R E PO SITIVE
A S C2 V O LTAG E
INC REASES)
Figure 65 Voltages w ith S5 dosed, shutter cocked
Figure 66
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,
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
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.
FRO NT OF C A M E R A
1 20
2 19
18
3
4 17
1
5 16
6 15
7 14
8 13
9 12
10 11
--
when the timing capacitor
on the charge across
1.1 —1.36V (M M O D E )
1.1 —1.4V (A. S M O D ES)
] 0.5 —0.7V
| 1.33—1.36V
] 1.1 — 1.2V
I ov
.] 1.9 — 2.4V
J
OV
l
2.8 —2.95V
kXP O SU RE)
J
1.1 — 1.36V (S M O D F I
1 . 0 - 1 . 1V (A . M M O D ES)
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.
voltage across the memory capacitor pro­
vides a larger base drive for transistor #1,
Fig. 64. The timing
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
the
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
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 're
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.
Increasing the
capacitor then
rides o ff the
fa m ilia r w ith the