V. IC CHECKS
IC101
Pins 1, 2,3. Battery check mode signals outputs. Voltage
is normally near zero,
Pins 4,5,6. Control to IC-102 for which signals should be
decoded. Typical traces shown,
Pins 7, 8. Integration capacitor selection control lines.
Sets code for selection during release. To test, apply Vcc
to SW-101 wire through 1000 ohm probe. ASA 6, pin 7
low, pin 8 high. ASA 100, pin 7 high, pin 8 low,
Pin 9 has no connection,
Pins 10,11,12. Exposure output to LCD, Pin 10 is timing
signal, pin 11 is serial data, and pin 12 is sync. See scope
traces.
Pins 13 to 20 are inputs from logic switches, ("Mode,"
"Clear," etc,) Common lines are pins 17, 18, and 20.
Pins 21 and 22 are battery negative.
Pin 23 has no connection.
Pins 24, 25, 26. Momentarily connecting each to pin 20
sets lamp on, battery check, or self-timer.
Pin 27 is the input from IC-102 to set flash mode. Vcc
through a 1000 ohm probe should set flash symbol on
LCD.
Pin 28 is the flash LED input.
Pin 29 is the exposure data from IC-102, See scope trace.
Pin 30 is the input from IC-102 to signal SW-101 closed
(mirror up). First high stores exposure data, next high
returns to metering mode. You can drive the circuit
bonkers with random highs to pin 30,
Pin 31 is output to Memory LED on "Spot" button.
Pin 32 is output to Q-105 to operate LCD backlight lamp,
Pin 33 is output to Q-106 for strobe LED in viewfinder.
Depends upon input at pin 28.
Pin 34 is output to IC-102 to turn on battery check LED.
Should go high in "Check" mode if supply is above 2.75 v.
Pins 35 to 42 are DAC output lines to IC-102, See scope
traces.
Pin 43 is input from reset circuit, Vcc resets circuit,
Pins 44 and 45 are 500 KHz clock signal, probably for
CPU,
Pin 46 is Vcc in.
Pins 47 and 48 connect to the quartz crystal. 32,8 KHz
sine wave,
Pin 49 is Mirror Switch, SW-101, signal input. Goes low
as SW-101 closes.
Pin 50 is the same as pin 27.
Pin 51 is battery negative.
Pin 52 is CLK output.
Pin 53 is the power signal to IC-102 for all circuits. Series
of high pulses after release is pressed one-half stroke.
Pin 54 is signal to IC-102 to supply power to LCD. High
when on.
Pin 55 is output to IC-103 that sets photodiode according
to mode. High is "Average," low is "Spot."
Pin 56 signals IC-103 with low when SW-101 closes,
Pin 57 is integration compensation to IC-102.
Pin 58 is Piezo signal to IC-102.
Pins 59 and 60 are signals to IC-102 to charge MG-l's
capacitor and release. Low signals release.
OLYMPUS OM-4, PAGE 6
Summary of Contents for OM-4
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