Connections To The Led Readout Circuit - Minolta XD-11 Repair Manual

CONNECTIONS TO THE LED
READOUT CIRCUIT
Even w ith the mirror cage removed,
you can't reach IC2; the driver for the
LEDs mounts to the other side of the flex
circuit. Fig. 48. However, you can make
most of the tests w ith o u t
disassembly.
A t the A and M settings, IC2 considers
four values — the shutter-speed setting,
the film-speed setting, the diaphragm set­
ting, and the light level. It then turns on
the appropriate LED to indicate the cor­
responding shutter speed.
You can follow the connections in Fig.
52. The diaphragm information (AV) ap­
pears at pin 10 of IC2. A t pin 12, IC2
receives the light-level (BV) and film-
speed (SV) information. The shutter-
speed information (TV) from the shutter-
speed resistor RTV goes to pin 11.
When you select the S mode, IC2 also
receives the minimum-aperture informa­
tion at pin 9. Switch S12 at the fro n t of
the camera, Fig. 53, selects a resistance
value according to the minimum aperture
of the lens. W ith no lens installed, notice
that the S12 brush rests at the center of
the first resistance path, Fig. 53. Installing
the f/1 6 MD lens set to the smallest aper­
ture moves the brush to the second re­
sistance path — the resistor labeled R47
in Fig. 52.
The f/2 2 lens moves the brush to the
third resistance path; here, the S12 brush
connects pin 9 of IC2 directly to positive
battery, Fig. 52. W ith the f/3 2 lens, the
brush moves o ff the resistors to an open
portion of the board.
Notice in Fig. 52 that the part of the
mode selector labeled S8 connects the
minimum-aperture switch S12 to pin 9 at
the S setting. Then, w ith the release but­
ton partially depressed,
measure a voltage at pin 9 — a voltage
which corresponds to the position of S12.
This voltage — the MD common volt­
age — causes IC2 to indicate the proper
diaphragm opening fo r the light condi­
tions. But, if you fail to set the smallest
aperture, IC2 only lights the overexposure
or underexposure LED in the S mode.
What if the IC fails to receive the MD
common voltage signal? You'll then find
that the LED readout w on't display the
diaphragm setting at the S mode. Although
you can't reach pin 9 of IC2, you can check
the MD common voltage at the top of the
camera; just measure the voltage to the
connection from the minimum-aperture
resistor shown in Fig. 54.
Set the mode selector to the S posi­
tion, Fig. 55. Then partially depress the
release button and measure the MD com­
mon voltage. W ith o u t a lens, you should
measure around 1.4V. Minolta specifies
further
Figure 53
FLEX STRIP
Figure 54
you should
Figure 55
MO C O M M O N VOLTAGE