Minolta Dynax 7000i: Removal of mirror box and shutter, checking shutter magnets SL1 and SL2, adjusting curtains travel times

[forest bagger]

Hello Andreas,

to measure the solenoid coil it is sufficient to unsolder one of the two wires and pretends you from mixing up the wires during resoldering.

 

[Andreas Thaler]

Hello Andreas,

to measure the solenoid coil it is sufficient to unsolder one of the two wires and pretends you from mixing up the wires during resoldering.

Thank you, I did it thoroughly right away, see below

 

[Andreas Thaler]

Removing the mirror box was problem-free.

However, some circuit board connections and board fasteners had to be desoldered, which aren't always readily accessible.

I'll later share some highlights.

 

[Andreas Thaler]

Removal of mirror box and shutter, check of shutter magnets SL1 and SL2

Since I don't believe that IC4 is defective or has a soldering error, I decided not to measure it with the oscilloscope and just removed the shutter unit for examination.

Besides, I wanted to disassemble the 7000i for study purposes anyway.

Mirror box removed.

This part in the shutter mechanism area doesn't belong here. It may have interfered with the movement of the second shutter curtain.

It's likely a cover on the shutter frame that came off.

I'll look into it.

Shutter unit removed.

The cover frame around the shutter mechanism towards the two curtains has been removed.

The contact surfaces and armatures of the two magnets SL1 and SL2 are now visible.

Inspection of the white cable according to Larry Lyells' instructions in the SPT Journal reveals no abnormalities. The cable is undamaged and fully soldered.

This error is therefore ruled out as a possible cause of the short shutter speeds deviation.

I want to measure the resistance of the coils of both magnets. To do this, I'm looking at how the conductors are connected.

SL1 is connected via the white and red cables, SL2 via the yellow and red cables.

Measuring the coil of SL1 with a multimeter.

The target value is 146 ohms, which is exactly achieved.

The coil is OK.

SL2 also complies with the specification.


All that remains is to clean the contact surfaces of the magnets and reassemble the 7000i. If this resolves the issue, the mission was successful.

However, it's also possible that the cover on the shutter that came off was the cause of the problem.

We'll see.

Stay tuned!

 

[Andreas Thaler]

Removal of mirror box, some impressions

The mirror box removal is described in detail by Larry Lyells in the SPT Journal. Therefore, I'll limit myself to a few impressions.

Connecting a solder bridge to the two test contacts of the main switch.

This means that the 7000i can be triggered even without the main switch contact in the top cover.

The top cover can be temporarily attached to make adjustments. For example, switching from P to M and setting the shutter speed to 1/4000 second.

Three green LEDs illuminate the main LCD.

Under the main LCD, the 7000i is tightly installed with several circuit boards stacked on top of each other.

Circuit board fixed on soldered pins.

A pressure-connector plate under the main LCD …

… which lies on the release base plate underneath.

To be able to distinguish between cables of the same color before desoldering, I mark them with white paint.

Removal of screws on the bottom.

Removal of the manual-aperture key.

Mirror box separated.


+++

All information provided without guarantee and use at your own risk.

 

[Andreas Thaler]

Messuring curtains travel times

It would be a good idea to measure the curtains travel times before assembling the 7000i and adjust them if necessary. This could also provide information about whether the two shutter curtains are moving mechanically correctly.

The Copal S(quare) shutter should be the same type as on the Minolta 7000 AF.

Both curtains are tensioned by a lever and released electronically. SL1 and SL2 are electromagnets that hold the curtains and release them as soon as current stops flowing through the coils.

For this, I would have to set up my breadboard to examine the shutter in the camera tester; for the 7000 AF, see here:

Post in thread 'Copal S(quare) Shutter: Testing when removed?'
https://www.photrio.com/forum/threads/copal-s-quare-shutter-testing-when-removed.212393/post-2880972

There is a risk involved.

If I misunderstand how the shutter works, I could damage it through incorrect operation. I don't have a replacement. But I also want to learn something new.

 

[Andreas Thaler]

Adjustment of the first shutter curtain possible from the outside

The first shutter curtain (opener with SL1) can be adjusted via an opening in the upper plate without removing the shutter:

1. Curtain-travel time
Reach the 1st-curtain travel-time
adjustment through the hole in the
flex -- C in Fig. 4. Turn the
1st-curtain worm clockwise to add
tension. To reach the 2nd-curtain
adjustment, it's necessary to remove
the mirror box.

SPT Journal: January-February 1991

Society of Photo-Technologists Journal

learncamerarepair.com

The blue arrow points to the opening for adjusting the first shutter curtain. The top cover is removed.

The shutter from the side.

The pink arrow points to the standard ratchet wheel with a pawl for adjusting the spring tension. Here, it's for the second shutter curtain (with the SL2 magnet).

The blue arrow points to a rotating thread that is adjusted vertically via a screw. A screwdriver can be inserted through the opening in the board above.

Hopefully I can turn the adjustment screw in both directions to also reduce the spring tension if necessary.


This design makes adjusting the curtain travel times convenient

The first shutter curtain is easily adjusted to the second curtain using the opening and screw. The shutter does not need to be removed for this purpose.

If the second curtain travel time does not deviate significantly from the target value, the shutter speeds are also correct.

With this board version, I can adjust the 1/4000 second using two trim potentiometers on the board.


Decision

I think I'll skip the experimental setup to avoid any risk and adjust the shutter from the outside.

If the shutter has a mechanical problem, I'd have to disassemble it, but there's not much I can do anyway. I'd have to replace the entire shutter assembly. I don't have a spare.

Since this is a teaching project, any repair results are welcome. Efficiency and time aren't important here. I can disassemble the 7000i again if necessary.

More to come tomorrow.

Stay tuned!


+++

All information provided without guarantee and use at your own risk.

 

[forest bagger]

Both curtains are tensioned by a lever and released electronically. SL1 and SL2 are electromagnets that hold the curtains and release them as soon as current stops flowing through the coils.

I think this is incorrect.
Nobody would construct a shutter that needs power (a current of some hundred milliamperes) to stay tensioned what is the normal state of use of a camera.
Usually these electromagnets have a permanent magnetic core which holds the curtain as long as no power is given to the coil.
When the coil is powered its magnetism overrides the magnetism of the permanent magnet and the curtain is released.

 

[Andreas Thaler]

I think this is incorrect.
Nobody would construct a shutter that needs power (a current of some hundred milliamperes) to stay tensioned what is the normal state of use of a camera.
Usually these electromagnets have a permanent magnetic core which holds the curtain as long as no power is given to the coil.
When the coil is powered its magnetism overrides the magnetism of the permanent magnet and the curtain is released.

It's the same with the 7000 AF, see also my setup on the breadboard for electronic shutter release:

Copal S(quare) Shutter: Testing when removed?

I am currently working on the Minolta 9000 AF shutter, which has problems with a rotting damper that is sticking the blades together. An attempt to clean it from the outside while it was removed was unsuccessful; the shortest times of 1/4000 to 1/1000 s are not formed or are not formed...

www.photrio.com

With the 9000 AF it is as you assume. This version of the Copal S shutter sports permanent magnets:

Post in thread 'Copal S(quare) Shutter: Testing when removed?'
https://www.photrio.com/forum/threads/copal-s-quare-shutter-testing-when-removed.212393/post-2879088

 

[Andreas Thaler]

Excursus: How can we explain the problem where the short shutter speeds are not formed?

Larry Lyells cites problems with the power supply (pinched cable to the electromagnet SL1) or dirty contact surfaces as causes, among others.

Since the Copal S shutter on the 7000i uses two electromagnets to trigger the shutter curtains, I explain this error as follows:

• When both curtains are pulled up and ready to fire, current flows through the coils of the electromagnets. The resulting magnetic field holds the armatures. The contact surfaces of the magnets are in contact with one another.
• When the shutter is released, the power supply is interrupted, the magnetic field drops. The electromagnets release their armatures and the shutter curtains move down.
• The first shutter curtain (opener with magnet SL1) starts. The second shutter curtain (closer with magnet SL2) follows. The resulting slit moves across the shutter window and exposes the image. The narrower the slit, the faster the shutter speed.
• If the SL1 armature is held by a weaker magnetic field (reduced current supply due to a pinched cable) or if dirty contact surfaces counteract the magnetic force, SL1 will start firing slightly earlier than SL2. This enlarges the exposure slit, and the short exposure times are no longer built.
• This effect becomes visible at approximately 1/125 of a second, as my camera tester measurements also showed.

Deductions

This allows me to rule out residual magnetism in the SL1 armature, as this would have the opposite effect. SL1 would trigger later, the exposure slit would become narrower, and thus the exposure time would be shorter.

Since the power supply to both magnets is OK (resistance measurement was performed previously), the only possible cause is a dirty contact surface on SL1. If SL2 were dirty, it would trigger earlier than SL1, which would shorten the exposure time (narrower slit).

It could also be that the first curtain is releasing too late due to a mechanical problem, such as friction, which also slows the curtain's travel. In this case, this would affect the curtain travel time displayed by the camera tester. For that, I would have to test the removed shutter, and I want to avoid this risk (see above).


Conclusion

I'll clean the contact surfaces of magnet SL1 (and SL2) with Zippo lighter fluid and reassemble the 7000i. Afterward, the camera tester will show whether this has solved the problem.

 

[Andreas Thaler]

I think this is incorrect.
Nobody would construct a shutter that needs power (a current of some hundred milliamperes) to stay tensioned what is the normal state of use of a camera.
Usually these electromagnets have a permanent magnetic core which holds the curtain as long as no power is given to the coil.
When the coil is powered its magnetism overrides the magnetism of the permanent magnet and the curtain is released.

This test shows that SL1 and SL2 are electromagnets and not permanent magnets.

Neither magnet holds its armature without a power supply: