background image

C & C ASSOCIATES

troubleshooting

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

s

 is generated at pin 75, IC-102.

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,  c o n t r o l s  m a g n e t s  a n d LEDs,  a n d
communicates with IC-101,

IC-103, under the floor panel of the mirror box,

supports "average" and "spot" photodiodes with
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

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

s

 they are part of an analog-to-

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

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.

Содержание OM-4

Страница 1: ...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 7 IC 102 At the same time IC 102 watches aperture setting AV VR at pi...

Страница 2: ...e the equivalent ofexposure with a signal from pin 80 to pin 14 IC 103 Voltage on the integrator s output begins to increase at a rate proportional to light intensity at the film plane The same voltag...

Страница 3: ...ight ASA and aperture conditions then calculates an exposure If shutter speed is less than 1 60 the flash will be triggered during exposure Light from the flash is integrated by IC I03 the same as Aut...

Страница 4: ...ry check in the previous step there is a power circuit problem Test power consumption 4 Watch the viewfinder LCD as you change aperture ASA and scan different subject brightnesses The bar graph should...

Страница 5: ...Pins 16 and 17 Memory Yellow to Brown or Pins 18 and 14 Clear Yellow to Red or Pins 16 and 18 8 The circuit may be cleared by moving the Mode Switch to the battery check position 9 Take care to avoid...

Страница 6: ...o 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...

Страница 7: ...CPU Pins 21 and 22 are mode control from CPU Pins 56 55 IC 101 Pin 23 is signal from CPU to power LCD Pin 24 is power on signal from IC 101 Should go high when release is pressed one half stroke Pin 2...

Страница 8: ...Pin 60 is charge signal to C 201 for MG 1 Voltage will pulse high at release then fall to near zero to recharge C 201 Pin 61 is release signal to Q 201 for MG 1 Pulses low for release Pin 62 is B in...

Страница 9: ...ives under a circuit board between the prism and ASA resistor It is not easy to reach for tests but important inputs can be checked at ICs 101 and 102 Its output of course is the LCD Pin 1 is CLK inpu...

Страница 10: ...de Manual and Spot Auto speeds are normal LCD normal 1 A 1 B 2 A 2 B 2 C 3 A 3 B 4 A 4 B Shutter slow or open in Manual and Spot Average Auto Average speeds normal LCD normal Shutter fast or running t...

Страница 11: ...1 Power Circuit Malfunctions A External Observations No LCD No battery check No shutter operation except mechanical OLYMPUS OM 4 PAGE 11...

Страница 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...

Страница 13: ...or under Spot Auto speeds slow Auto speeds slow or normal Manual speeds normal First check bar graph response to light ASA and AV changes to isolate problem Follow the same pro cedure as 2 A but look...

Страница 14: ...onnects across pins 7 and 8 IC 102 Value is 0 015 MF 2 Check if bar graph is stable in BC mode If so check R 130 near IC 101 3 Check for dirty wipers on AV VR and SV VR 3 Release Malfunctions A Extern...

Страница 15: ...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 norma...

Страница 16: ...ual speeds normal Spot Auto speeds normal 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 c...

Страница 17: ...D External Observations Shutter fast or runs through Auto and Manual LCD is normal Mechanical operation is normal OLYMPUS OM 4 PAGE 17...

Страница 18: ...mal LCD is normal G External Observations Manual speeds not correct or won t respond to adjustment Auto mode speeds OKt 1 Check each Manual speed with LCD If LCD does not correspond to speed dial TV V...

Страница 19: ...5 Display Malfunctions A External Observations No LCD or weak or erratic Shutter functions normal Exposure is normal OLYMPUS OM 4 PAGE 19...

Страница 20: ...isplays 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 Flas...

Страница 21: ...r not working Self timer function is normal 1 For LED apply B to pin 41 IC ID2 through 1000 ohm probe If LED flashes IC 102 may be defective If no LED check B to LED Black wire from TP 1 Also Q 401 an...

Страница 22: ...OLYMPUS OM 4 PAGE 22...

Страница 23: ...OLYMPUS OM 4 OLYMPUS OM 4 PAGE 23...

Страница 24: ...s a violation of the law Willful violations of the been taken in the preparation of this manual the publisher Copyright Law of the United States can result in civil assumes no responsibility for any e...

Отзывы: