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Olympus OM-4 Troubleshooting Manual
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C & C ASSOCIATES
ELECTRONIC TROUBLESHOOTING THE OLYMPUS OM-4
1. CIRCUIT DESCRIPTION
Power Circuit
As with other OM-series cameras, battery positive
connects to the chassis and to the flex circuit through
screws holding the circuit in place. In this guide, battery
positive is designated as Vcc and connections to the
chassis are shown as the "earth" symbol,
A black wire connects battery negative to the Shutter
Terminal Board and to the main flex near the rows of
variable resistors, From there, conductors fan out to pins
22, 51, IC-101; pins 6, 26, 62, IC-102; and pin 13, IC-103.
The Display Flex and Reset Board receive battery
negative through a black wire soldered to the Main Flex
near IC-101,
When batteries are installed, a quartz oscillator
involving two capacitors and IC-101 is activated.
Pressing the release button one-half stroke closes switch
SW-I11 to connect pins 15 and 18, IC-101. IC-101 then
signals IC-102 to power up the metering circuit and the
LCD for about 2 minutes. Power signals are from pins 53,
54, IC-101 to pins 24, 23, IC-102. Pressing the release
button renews the 2-minute power latch, A 1.8v constant
voltage, Vref
is generated at pin 75, IC-102.
s
A diode is connected to the battery terminals in reverse
direction to protect the circuit if batteries are installed
backward.
Battery requirement: two S-76 silver oxide or two
LR44 alkaline-manganese.
Metering Circuit
There are four ICs involved in metering, exposure
control, and display. IC-101 contains a microprocessor
(CPU) and understands only binary signals as inputs and
outputs. It keeps track of mode, calculates exposures,
and owns the clock. IC-102 is a bipolar IC which contains
comparators for A / D conversion, watches over variable
resistors,
controls
communicates with IC-101,
IC-103, under the floor panel of the mirror box,
supports "average" and
amplifiers and temperature compensation circuits. It also
takes care of integration for automatic exposure in
ambient and flash modes. IC-104 is a decoder/driver for
the comprehensive LCD.
Prior to exposure a sub-mirror behind the reflex
mirror reflects a portion of light going to the viewfinder
to the photodiodes on IC-103, A BV voltage, changing
18mv/Ev with light, is output from pin 16, IC-103 to pin
troubleshooting
m a g n e t s
a n d
LEDs,
"spot"
photodiodes with
7, IC-102, At the same time, IC-102 watches aperture
setting (AV-VR at pin 74), ASA (SV-VR at pin 67), and
shutter speed setting (TV-VR at pin 73). Although
variable resistors are used
digital conversion process which changes all exposure
information to binary codes for the CPU.
The code is sent back as series data from pin 38, IC-102
to pin 29, IC-101 so the CPU knows ASA, aperture
setting, and shutter speed setting. How the CPU
interprets the data depends upon operating mode
selected, IC-101 will calculate an exposure, then send a
coded message to IC-104 which drives an LCD display to
indicate exposure and other information, A quartz clock
operating at 32.8 KHz keeps the operation orderly and
the whole process is repeated every 100ms to keep data up
to date,
IC-101 sends digital-to-analog data along eight lines
(DAC-0 to DAC-7). During exposure in Manual and
Spot modes, IC-103 will need analog voltage to set
exposure times.
Details such as different voltage levels between average
and spot SPDs are taken care of by voltage boosting
circuits. Because of a wide exposure range, integration
capacitors are switched in and out of circuit according to
ASA setting,
Release Circuit
Pressing the release button full stroke mechanically
unlatches the mirror as with other OM-series cameras, As
the mirror rises, switch SW-101 closes to connect Vcc
(B+) through two diodes to bases of transistors Q-103 and
Q-904. As the transistors turn on, pin 49, IC-101 is set low
and pin 58, IC-102 is set high. In this manner the ICs are
told the mirror is on its way up and they had better gel
ready for an exposure. IC-101 stores exposure data and
and
LEDs are temporarily disabled to conserve power.
IC-101 also sets an exposure program according to mode.
IC-102 tests battery voltage to be sure it is above 2.65v,
then pin 61 goes low. Pin 61 is connected to the base of
transistor Q-201 (PNP) on the shutter board, Q-201
switches on causing capacitor C-201 to discharge through
the coil of combination magnet M-l. M-l repels its
keeper which unlatches the opening curtain, IC-102 then
waits for switch SW-103, the Trigger Switch (Timing
Switch), to signal the first curtain is moving before
initiating exposure control.
they are part of an analog-to-
s

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Summary of Contents for Olympus OM-4

  • Page 1 C & C ASSOCIATES troubleshooting ELECTRONIC TROUBLESHOOTING THE OLYMPUS OM-4 1. CIRCUIT DESCRIPTION Power Circuit 7, IC-102, At the same time, IC-102 watches aperture As with other OM-series cameras, battery positive setting (AV-VR at pin 74), ASA (SV-VR at pin 67), and connects to the chassis and to the flex circuit through shutter speed setting (TV-VR at pin 73).
  • Page 2 Light from the subject is focused on As the mirror returns and SW-101 opens, the ICs are the opening curtain (and later the film) through the reset to auto exposure using average light readings. OLYMPUS OM-4, PAGE 2...
  • Page 3 Average mode. When a proper exposure has been made, pin 48, IC-102 goes high signaling the flash through its dedication contact. The flash quenches, the shutter times out at 1 /60 second, and the system resets for the next exposure. OLYMPUS OM-4, PAGE 3...
  • Page 4 CPU and are indicated by the LCD, half stroke. The LCD in the viewfinder should show a bar Those exposures should always equal the indication. graph and list shutter speeds from 1 through 2000, If OLYMPUS OM-4, PAGE 4...
  • Page 5: Adjustment Procedure

    46, IC-102, At room temperature, 21 "Memory" . Yellow to Brown or Pins 18 and 14 degrees centigrade, the voltage should be 198mv, Adjust "Clear" ..Yellow to Red or Pins 16 and 18 with VR-108. OLYMPUS OM-4, PAGE 5...
  • Page 6 Pin 58 is Piezo signal to IC-102. sine wave, Pins 59 and 60 are signals to IC-102 to charge MG-l's Pin 49 is Mirror Switch, SW-101, signal input. Goes low capacitor and release. Low signals release. as SW-101 closes. OLYMPUS OM-4, PAGE 6...
  • Page 7 Pin 44 is integration current charging C-104 for "Manual" and "Spot" shutter timing. See scope trace. Pins 21 and 22 are mode control from CPU, (Pins 56, 55, Vcc through a 1000 ohm probe should result in fast IC-101.) manual speed. OLYMPUS OM-4, PAGE 7...
  • Page 8 1.8v. Pins 71 and 72 are reference current to TV-VR. Typical voltage is near 1.8v. Pin 73 is input from TV-VR. See scope trace. B- through a 1000 ohm probe should result in fast manual speeds. OLYMPUS OM-4, PAGE 8...
  • Page 9 Pin 13 is data clock signal in. Check at pin 10, IC-101 and the blue wire. If there is no display, check for proper connections to pins 3 and 4 and from there to capacitor C-3Q2. This is the 6-volt power source for the LCD, OLYMPUS OM-4, PAGE 9...
  • Page 10 Shutter slow or open in Flash control problems: "Auto Average" mode see IC-Checks and Circuit Description, "Manual" and "Spot Auto" speeds are normal Self -Timer not working LCD normal LED or Piezo Buzzer are not functioning Self -Timer delay normal OLYMPUS OM-4. PAGE 10...
  • Page 11 1. Power Circuit Malfunctions A. External Observations No LCD, No battery check. No shutter operation except mechanical OLYMPUS OM-4, PAGE 11...
  • Page 12 B. External Observations: Batteries run down quickly, Shutter functions may or may not be normal. LCD may or may not function. OLYMPUS OM-4, PAGE 12...
  • Page 13 1, Low voltage at pin 7, IC-102. 2, Open connections to VR-105 and VR-106, 3, Open connection to, or poor contact of, AV-VR wiper. 4, Solder bridge around SV-VR terminals or shorted wiring, 5, Short between pins 67, 68, 69, IC-102. OLYMPUS OM-4, PAGE 13...
  • Page 14 3. Check for dirty wipers on AV-VR and SV-VR, 3. Release Malfunctions A. External Observations: Shutter will not release (or erratic) in "Auto" or "Manual," although mirror is up. Mechanical shutter function is normal LCD is normal. Supply voltage is above 2.65v. OLYMPUS OM-4, PAGE 14...
  • Page 15 B. External Observations: Shutter releases once, then will not release again until circuit is reset, LCD normal. 4. Shutter Malfunctions A. External Observations: Shutter stays open in "Auto" and "Manual" Mechanical speeds OK, LCD normal. OLYMPUS OM-4, PAGE 15...
  • Page 16 LCD normal C. External Observations: Shutter slow or open in "Manual," Shutter slow or open in "Spot Auto," "Auto" speeds normal LCD normal. Note: Be sure LCD indicates correct "Manual" speed. If not, TV-VR is dirty. OLYMPUS OM-4, PAGE 16...
  • Page 17 D. External Observations: Shutter fast or runs through "Auto" and "Manual" LCD is normal, Mechanical operation is normal. OLYMPUS OM-4, PAGE 17...
  • Page 18 TV-VR is dirty or not making contact. 2. If slow speeds are off, check VR-101 soldering. 3. If fast speeds are off, check: A. VR-102 B. R-102 C. C-102 D. Trigger Switch chatter E. Curtain overlap OLYMPUS OM-4, PAGE 18...
  • Page 19 5. Display Malfunctions A. External Observations: No LCD or weak or erratic, Shutter functions normal. Exposure is normal. OLYMPUS OM-4, PAGE 19...
  • Page 20 LCD works, but displays wrong characters for mode. Shutter function appears to be normal. Look for poor solder connections at wires to Display Board. 6. Flash Malfunctions A. External Observations: Flash will not fire, "Flash" mode selected OK. OLYMPUS OM-4, PAGE 20...
  • Page 21 If no LED, check: B- to LED (Black wire from TP-1.) Also, Q-401 and LED. 2. For Piezo Buzzer, check output at pin 52, IC-102. If signal is present, check connections to Tinier Board and Buzzer Switch, OLYMPUS OM-4, PAGE 21...
  • Page 22 OLYMPUS OM-4, PAGE 22...
  • Page 23 OLYMPUS OM-4 OLYMPUS OM-4, PAGE 23...
  • Page 24 C & C and/or a $10,000 fine. Associates reserves the right to make changes or improvements in this manual at any time without notice. OLYMPUS OM-4, PAGE 24...