Now In Fig wc have removed ihe insulating

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tape from the bottom of the flex circuit. Removing the insulating tape allows access to the circuit-test points. But be sure to replace the insulating tape. Fig. 5, before installing the bottom cover. Otherwise, the bottom cover may short the circuit to ground.

As the connecting lever charges the release magnet MG2, it also charge* the mirror. A post on th< connecting lever extends through a slot in the bottom of the body casting to engage the mirror-cocking mechanism. From the bottom of the camera, you can see the end of the mirror-lifting lever. Note that the mirror-lifting lever moves towa rd the front of the camera as you cock the shutter.

The mirror-lifting lever comes against the spring on the MG3 armature. So, as the mirror-lifting lever moves forward, it pushes the MG3 armature toward the core of the shutter magnet.

During the cocking stroke, the connecting-lever arm prevents the MG3 armature from touching the second-curtain cam. Then, at the end of the wind stroke, the spring-loaded connecting lever return* toward the wsnd-lever end of the camera Now the MG3 armature moves against the core of the shutter magnet. And the latching surface of the MG3 annature drops into engagement with the sccond-curtain cam.

After the MG3 armature engages, switch SWS, Fig. 16, opens. In the AE-1, SW5 do*es at the end of the cocking cycle to provide a ground connection as well as to signal the power winder; poor S W5 contact then causes a failure of the shutter to release. ButintbeAE*! Program, the shutter can only release when SW5 opens. Poor contact in SWS »nay then affcct the power-winder operation, but the shutter will still operate.

The count switch SW4, Fig, 16, closes with the shutter cocked. As in the AE-1, SW4 serves as a timing switch. When SW4 opens, the circuit starts timing the shutter speed When you close SWI and SW2. capacitor CI discharges through the coil of the hybrid release magnet MG2. MG2 now repel* its armature. The armature moves toward the front of the camera and releases the mirror.

The mirror moves up and strikes the first-curtain latch. Fig. 16. As the first-curtain latch disengages the first curtain, it opens the count switch SW4. Now the timing circuit starts counting digital pulses. As the timing circuit counts* current flows through MG3. MG3 holds the MG3 armature engaged with the second-curtain cam to hold the second curtain.

Once the timing circuit reaches the proper count, it shuts off the MG3 current. MG3 now releases the second curtain. At the end of the exposure. SWS closes to signal the power winder.

Canon Shutter Tension

sccohd-curwim AOiUST

Curtain-travel Times, adjustment:

Adjust the curtain-travel times at 1/1000. You can reach the tension-setting gears through the clearancc cutouts in the MG2 base, Fig. 17. Turn the tension-setting gears counterclockwise to add tension (faster travel times) or clockwise to let off tension (slower travel times).

Since the shutter uks Delrin gears, the recommended travel times are faster than in the AE-I. Set the curtain-travel times to !0.5ms for a 34mm distance (Canon standard). If your tester measures across a 32mm distance, set the travel times to 9.9ms.

MG2 and MG3, test procedure*

Unlike the AE-I, magnets MG2 and MG3 rcceivc power only with SWI closed. Without closing SWI, you should measure OV to both magnets Closing SWI connccts the El voltage (close to the battery voltage) to MG2 and MG3,

To check MG2, close SWI. Now, with the shutter cocked, short the MG2 signal lead. Fig. 17, to the ground screw. MG2 should repel its armature and release the mirror.

Alternately, you can simply measure the voltage to each MG2 lead. If you don't measure the operating voltage at the El lead with SWI closcd. the problem is in the circuit. But if you measure the voltage at the El lead and not at the signal lead. MG2 has an open coil. You can measure the coil resistance (90 Q) between the two MG2 leads.

You can also check MG3 by metraxisg the voltages to the two leads, Ftg, 18. An open in MG3 causes a failure of the shutter to release. Cheek for the El voltage at the red lead with SWI closcd. If you get the El voltage at the red lead, but not at the black lead, MG3 has an open coil.

Flgur« t7

Disassemble Canon Program

Second-curtain latch. adjustment

The AE-I Program uses a minus latch for the second curtain. A minus Latch means that, with the shutter cocked, there's no space gap between the latching surface of the MG3 armature and the latching surface of the second-curtain cam, Fig. 18. All Canon A-series cameras that provide automatic shutter-speed control use the mi-nus latch to improve the accuracy.

As you cock the shutter, you should see the sccor.d-curtain cam rotate slightly beyond the latching surface of the

MG3 armature. However, with the shuuer c«kcd, then: should be no space gap between the latching surfaces. To check for proper engagement with the shutter cocked, pull the MG3 armature out of engagement with the sccond-curtain cam. When you allow the MG3 armature to spring back into engagement, it should «gain fully engage the cam notch.

Adjustment on the sccond-curtain cam should not be necessary unless you have replaced shutter parts. To make the adjustment, first loosen the two setscrews that hold the second-curtain cam to the sccond-curtain shaft. Then route the second-curtain cam.

Wind Sequence, test

As you cock the shutter, the following actions should occur in sequence:

1. The first-curtain latch should engage the first-curtain gear.

2. The MG3 armature should engage the second-curtain cam as the connccting lever returns.

3. The transport latch should engage the wind-shaft notch (top of camera), allowing SW5 to open.

To check the sequence, slowly advance the wind lever. Watch the first-curtain latch. Fig. 16. When you see the first-curtain latch drop into engagement, stop advancing the wind lever. The MG3 armature should not as yet be engaged with the second-curtain cam.

Next advance the wind lever until the connecting lever snaps back toward the wind-lever end of the camera. The moment the connecting lever returns, check SW5—SW5 should still be closed. As you then complete the wind stroke. SW5 should open.

SWS. adjustment

S W5 has an eccentric adjustment for proper operation. Fig. 16. To check the adjustment, slowly advance the wind lever. Stop advancing the wind lever the moment the connecting lever returns. Now try to release the shutter by closing SWI arid SW2. If SW5 is properly adjusted, the shutter will not release.

Whet? you complete the wind stroke. SW5 should open. Now you should be able to release the shutter. To make the adjustment, first advance the wind lever until the connecting lever just returns. SW5 should still be closed. Turn the SW5 eccentric contact counterclockwise until it touches the wire contact

Next turn the eccentric contact slightly further in a counterclockwise direction—a distance equal to the width of the eccentric screwdriver slot. The additional distance assures good contact pressure.

Now complete the wind stroke. When SW5 opem, there should be a space gap of at least 0.15mm between the wire contact and the eccentric contact.

Connecting-lettr Arm, adjustment

The connecting-lever arm prevents the MG3 armature from contacting the second-curtain cam during the cocking cycle. To check, advance the wind lever until the charge cam has pushed th« connecting lever the maximum distance—as far as the connecting lever will move toward the rewind erui of the camera. There should now be a space gap of 0.2-0.4mm between the edge of the second-curtain cam and the MG3 armature. Fig. 19. Adjust by bending the connecting-levsr arm.


Figure 20

Figure 20

Canon Circuitry


The circuit provides digital control of shutter speeds and diaphragm openings using four ICV-

ICi. Analog acd digital IC! oca ted on the rewind side of the ilex. Fig. 20. ICI contains the amplifier for the linear signals, the digital driver for the three magnets, and the oscillator for the 32 KHz clock signal. 1C2. Digital CPU (central processing unit) located on the wind side of the flex. Fig. 21. IC3. Digital decoder/driver for the LED display, located on the LED display board (under the film-speed base plate).

IC4. Linear amplifier for the SPD (silicon photodi-odc) located above the cyeiens The SPD is built into IC4. IC4 also supplies the constant-voltage source for the Vc reference voltage.

The block diagram. Fig. 22» show* ihe bask operation. A MOS amplifier serves as a log compressor, converting the SPD current to a voltage. The linear outputs of the MOS (BV), the film-speed resistor (SV), and the maximum-aperture resistor (AVO) are added and converted to a digital signal.

FlflUf« 22

Amplifier A-D, the analog-to-digital converter, provides the signalconversion. The digitalsignal from amplifier A-D goes to a digital memory. A storage register memorizes the digital signal thai corresponds to the brightness value, the speed value, and the maximum aperture.

The count stored in the BV/SV/AVC (aperture value correction) register provides one reference for determining the actual aperture. The second factor—the shutter-speed setting—comes from the TV switches. Setting the shutter speed by turning the shutter wiper opens or closes switches, supplying the TY signal in natural binary codc, A codc converter converts the natural binary code to Gray code.

A separate register, the TV register, stores the count for the shutter-speed information. Now the digital calculator determines the proper f/stop from the information in the two registers. The digital calculator «ores the f/stop information in the AV register. A decoder/driver decodes the digital count in the AV register and turns on the proper LED in the viewfindcr display.

At the program setting» the digital calculator refers to a fixed program to determine the combination of shutter speed and diaphragm opening. It then stores the shutter-speed information in the TV register and the diaphragm information in the AV register.

When you close SW2 to release the shutter, the registers lock In the digital counts. The sequence controller now has the references it needs to control the magnets. First the sequence controller, after giving the registers time to reach their maximum counts, notifies the magnet driver to send current through MC2. On the self-timer setting, the sequence controller waits 10 seconds before giving the release signal.

Next the sequence controller must determine when to shut off the diaphragm-control magnet MG1. As (be diaphragm closes, it mows the S.AVE (segmented aperture-value electrode) contact. The S.AVE contact now sends a digital signal to the sequence controller.

The sequence controller compares the count received from the S.AVE contact to the count stored in the AV register. When the two counts are equal, the sequence controller shuts off the current flowing through MO I. MGl then releases its armature to stop the diaphragm at the proper diaphragm setting.

When the mirror releases the first curtain» the sequence controller determines how long the shutter magnet MG3 should hold the sccond curtain. The sequence controller counts clock pulses supplied by an oscillator. A comparator comparts the number of clock pulses to the count stored in the TV register. When the counts art equal, the sequence controller signals the inagnefdriver to shut off the current flow through MG3.

Switch Locations and Functions

The switch numbers in the AE-l Program correspond to those in other A-series Canons.

SWl— metering switch, controlled by the release button. Wh«n you push the release button part way, SWl closes to supply El voltage to the ICsand magnets. SWl1—preview switch at the side of the lens mount. Performs the same function as SWl. SW2— release switch, controlled by the release button.

SW2 is under SWl. SW4— count switch at the front of the first-curtain latch. Closed with the shutter cocked, opens when the first-curtain latch moves forward to release the first curtain. When SW4 opens, the liming circuit starts counting clock pulses.

Shutter 300d Capacitor

Circuit Power

SW5— power-winder, motor-drive switch operated by the transport latch. Closed with the shutter released, opens when you cock the shutter.

SW7— self-timer switch. Closes when you turn the SL contact to the self-timer position.

SW8— battery-test switch on top of the film-speed base plate. Closes when you depress the battery-test button, turning on the sound-drive oscillator to power the piezo beeper.

SW9— memory switch on the side of the lens mount. Pushing the AE-lock button closes SW9 to lock the information in the storage register*.

SW11— auto/ manual switch at the back of the front plate. Setting the lens to a manual f/stop closes SW11. SW11 opens at the auto setting of the lens.

SW12—TV switches controlled by the shutter wiper.

SWO— on/off switch controlled by the SL wiper. When you turn the SL contact to the A setting, SWO closes.

Circuit Power

The battery voltage appears at the red wire to the SL switch board. Fig. 23. You should measure the full battery voltage between ground and the red wire rega rdless of the switch position. Turning the SL wiper to the A position. Fig-23% connects the battery voltage to the emitter of transistor TRI, Fig. 24, by closing switch SWO.

When you now close metering switch SW!, TRI turns on. The El voltage (battery voltage minus the voltage drop across the transistor) appears at the TR1 collector. Turning on TR! supplies the El voltage to the four ICS and to the three magnets.

The check system built into 1C1 prevents the camera from operating if the battery voltage drops too low. The check system also prevents operation if thcre^s an open in MG2 or MG3; an open magnet results in a failure of the shutter to release. Similarly, the check system prevents the shutter from releasing if the count switch SW4 makes poor contact.

Constant Voltages

With SWI dosed, the circuit supplies two constant voltages—Vc, the 1.3V reference voltage for the amplifiers and comparators, and KVc, the 1.6V adjustment voltage.

IC4 supplies the L3V Vc voltage. With SWI closed, you should measure the Vc voltage at the Vc test point, Fig. 21. No voltage reading indicates a defective IC4.

IC1, Fig. 20. supplies the 1.6V KVc voltage. The KVc voltage is applied to variable resistor VRI, the auto-exposure adjustment. You should measure KVc at the VRI lead indicated in Fig. 20 with SWI closed. No voltage reading indicates a defective ICI.


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Ftgurv 25


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Oock Signal

1CI contains the oscillator that supplies the clock signal. You can check the clock signal at the OSC test point, Rg. 20. If you're using an oscilloscope, you should measure the 32 KHi square-wave signal shown in Fig. 25. However, you can make a voltage reading to check for the presence of the clock signal. A voltage of 0.7V at the OSC test point indicates that the clock signal is present.

The clock serves as the timing signal for the circuit functions. Each timing circuit counts clock pulses rather than sensing voltage levels. A frequency divider counts down the basic 32 KHz frequency to provide the different time controls.

When you close SW2 to release the abutter, the oscillator provides the slight delay that allows the counters time to reach their maximum counts. On the self-timer function, the oscillator delays the MG2 current for 10 seconds.

The oscillator signal also goes co the decoder/driver for the LED display. Here, the frequency divider provides the signal that allows the decoder/driver ta sample new information every 0.5 second. Abo, the frequency divider provides the 2 Hz signal that causes the LEDs to flicker as warning indications.

At the CPU, the clock provides the timing signal for the shutter speeds. The CPU counts dock pulses and compares the count with the references stored in registers

A failure of the oscillator then causes the same matfunc-tion as a bad battery—the shutter worft release, and the LEDs won't turn on. If nothing workaclectrorucally, checking the clock signal should be one of your first tests.

Light Measurement

The light-measuring circuit uses a silicon photodiodc (SPD or SPC) that measures the brightness value from the focusing screen. IC4, the linear amplifier for the SPD signal, contains the built-in photodiodc.

To reach IC4, lift out the SPD cover that clips to the top of the eyelens assembly. Fig. 20. You can then lift up the section of flex containing IC4, Rg. 26. When you reseat the flex, position 1C4 behind the tab on the SPD fresnel-lens frame; position the ends of 1C4 between the two positioning lugs.

The MOS amplifier in IC4 converts the current changes through the SPD to voltage changes. As the light level increases, the output of the MOS goes more positive. The diode in the MOS feed back circuit provides log compression to compress the brightness range of the subject to a range the circuits can handle.

Amplifier AR5, also inside 104, Fig. 27, amplifies the output of the MOS. The BV voltage signal appears at pin 4 of A R5. Since ARS is an inverting amplifier, the BV output goes more positive as the light level decreases.

Ftgurv 25

Passive Bandpass Filter Graph

You can check the pin 4 voltage without lifting oui 1C4. Measure the voltage at the end of resistor R7, Fig. 20, with SWI closed. The voltage should be a round IJ V with the top cover removed. If you cover IC4 to reduce the light reaching the SPD, the voltage should increase; Ihe voltage should decrease if you allow more light to strike the SPD.

IC4 »bo contains the AVO amplifier for the maximum-aperture information. The post on the back of the lens determines the resistance of the maximum-aperture resistor VR102, Fig. 28. In turn, VRI02 determines the output of amplifier AVO.

The output of AVO goes to the AVC (aperture-value correction) amplifier inside ICI, Fig. 28. Next the film-speed resistor inputs the film-speed setting as a resistance value. Fig. 28. All three variables—the brightness value, the film speed, and the maximum-aperture information—go to summing amplifier ARI, Fig. 29.

AR1, a linear amplifier, adds together the three variables. The linear output signal must then be converted to a digital signal for processing in the CPU. An analog-to-digiial converter in IC2 provides the signal conversion.

A-D Converter

Amplifier AD in IC2, Fig. 29, uses a capacitor CAD (capacitor analog-to-digital) in the feedback path. The linear metering signal at the inverting input of AD controls the chargc time of CAD.

If the light level increases, the metering signal goes more positive. CAD then charges more quickly. When the light levtl decreases, the input signal goes less positive. And CAD charges more slowly.

Yet the discharge time of CAD remains constant-regardless of the input signal. CAD always discharges through a fixed resistor. One slope of the output signal. Fig 29, then varies according to the input signal. The other slope remains constant.

Changing one side of the output slope varies the length of the peak. Fig. 29. The output of AD can then be converted to a digital pulse—the length of the pulse depends on the input variables.

Figure 2S

cad cad

The digital signal goes to the CPU where it's stored in a register. As the CPU processes the information, it refers to the exposure register for the light level, film speed, and maximum aperture.

You can check the A-D signal as one test of IC2. Touch the oscilloscope probe to pin I of IC2, Fig. 21, and close SWI. At the scope settings of 0.05 v/cm and 2ms sweep time, you should get the A-D signal. One side of the trace should change as you change the light level.

Aperture Control

When you depress SW2 to release ihe shutter, the circuit locks the exposure information in the storage registers. The CPU now calculates the proper f/stop from the information received from the A-D converter and the information received from the shutter-speed setting. The result of the calculation determines the count stored in the A V register, Fig. 30.

The circuit then knows what f/stop to set. But the CPU still needs to know the actual diaphragm, position—how far the diaphragm has closed. This information come* from the segmented aperture-value electrode—S.AVE, Fig. 30.

As the diaphragm closes, the S.AVE wiper moves along a series of contacts. Fig. 30. The resulting digital signal goes to a comparator. The comparator compares the S.AVE count to the count stored in the AV register.

When the two counts are equal, the comparator shuts off the current flowing through the diaphragm-control magnet MG1, Fig. 30. MG1 then releases its armature to arrest the diaphragm at the proper f/stop.

Shutter-speed Control

The signal that tells the CPU what shutter speed youVe selected doesn't have to go through ai\ analog-to-digital converter—it's already a digitaL signal. The shutter wiper. Fig. 23, controls the signals at pins 12, 13,14, and l5ofJC2. The signal at each pin is either high (around 1.6V) or low (0V).

Fig 31 shows how the shutter wiper controls the pin signals. The shutter wiper opens or closes the four TV switches. When a particular TV switch is open, the signal at the pin connected to the switch is high. Closing that switch then shorts the pin signal to ground for the low input.

IS »14 | 13 | 12

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Figure 32

Each setting of the shutter wiper results in a different combination of signals at the four IC2 pins. Fig. 32 compares the input signals at four settings. You can check the input signals by measuring the pin voltages of IC2, Fig. 23. If a particular pin fails to switch to OV. the problem may be poor contact in the TV switch connected to that pin. But if a pin fails to switch to 1.6Vt the problem is probably a defective IC2.

The CPU processes the digital signal from the TV switches and stores the count in the shutter-speed (TV) register. Now the CPU knows how long it must allow MG3 to hold the second curtain.

Fiflur« 33

When the mirror releases the first curtain, the first-curtain latch opens the count switch SW4, Fig. 33. Opening SW4 allows capacitor C3 to start charging When C3 reaches the trigger voltage, the timing circuit starts counting clock pulses supplied by the oscillator.

A comparator compares the clock count with the count memorized in the TV register, Fig. 33. When the two counts arc equal, the comparator shuts off the current flowing through MG3. MG3 then releases the second curtain to end the exposure.

The sooner the count switch opens, the sooner C3 starts charging. On fast shutter-speed settings, the moment that the count switch opens has a significant effect on the exposure time. Here, the clock count quickly reaches the count stored in the TV register. At slow-speed settings, however, the moment that the count switch opens has very little effect.

You can therefore adjust SW4 as a. fast-speed control. At the 1/J000 setting, you can bend SW4 to correct the accuracy. Bending the SW4 wire conia.ct toward the first-curtain latch causes the count switch to open sooner—a faster shutter speed. But you normally dont have to bend SW4. Variable resistor VR2, Fif. 33 and Fig. 21. provides a fast-speed adjustment. VR2 affects the charge time of C3. The faster C3 charges, the sooner the circuit starts counting clock pulses.

VR2 has very little effect on the slow speeds. There's only one slow-speed adjustment—the frequency of the oscillator that supplies the clock pulses. You can change the oscillator frequency by changing the value of resistor R2, Fig. 25 and Fig. 20. The adjustment procedure is described in Section 13. However, unlets you replace IC1, you should never have to make the frequency adjustment.

Sound-drive Circuit

A separate oscillator inside IC2 drives the piezo beeper—both for the self-timer function and for the battery-test function. When you close the battery-test switch SW8, load resistor R11 draws battery current, Fig. 34. R11 connects across the top of IC2, Fig. 21.

If the battery voltage under load is at least 3.5V, the sound-drive oscillator in IC2 supplies a 4 KHz signal to the piezo beeper, Fig. 34. A steady 4 KHz signal would cause the beeper to emit a continuous tone. To gel the beeping indication, IC2 interrupts the 4 KHz signal. The frequency of the interruption signal changes to get the different beeping frequencies.

A battery voltage of 4.8 V or higher causes the circuit to interrupt the 4 KHz oscillator 6.5 times a second. The frequency of the intemiption signal decreases as the battery voltage decreases.

Closing the self-timer switch SW7f Fig. 34, again turns on the 4 KHz sound-drive oscillator. But the self-timer oscillator signal is 5V peak-to-peak compared to 2.5V peak-to-peak for the battery test. The piezo then beeps louder on the self-timer function.

For the first 8 seconds of the self-timer delay, the circuit interrupts the 4 KHz signal at a rate of 2 Hz. The frequency of the interruption signal increases to 8 Hz for the final 2 seconds of the delay.

The piezo beeper sits under the film-speed base plate Unlike most cameras using piezo beepers. The AE-I Program has no sound-emitting hole. Rather, the entire camera body serves as a resonator for the beeper

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  • orla
    How to fix the shutter curtain on a canon ae1 that is slightly open?
    7 years ago

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