Copal S(quare) Shutter: Testing when removed?

[Andreas Thaler]

Now everything is ready for checking and adjusting the shutters on the Minolta 9000 AF and 7000 AF on the camera tester.

However, they must first be removed. Then we can proceed.

 

[Andreas Thaler]

Minolta 7000 AF: Curtain travel times set on my work camera

Today I applied the knowledge I've gained so far to my work camera.

At 1/2000 second, there was an exposure deviation of over +1 EV in the upper part of the image. This was due to the two shutter curtains not moving synchronously.

I had to remove the mirror box again to access the shutter.

The shutter went into my specially made test back.

The test setup with laboratory power supply, experimental board and Reveni Labs Camera Tester. This allows me to trigger the shutter electronically using two switches.

The two shutter curtains are cocked manually, a task that would otherwise be performed by the Minolta 7000 AF's motor.

The experimental board has various terminals and components, such as these two switches, which I connected to the shutter via cables. This allows me to trigger the two curtains separately.

Adjusting the two locking wheels against the spring force requires full concentration. It's done in clicks to count.

When I had both curtains almost synchronized, I slipped with the screwdriver and made several clicks instead of one. So I had to start over. You can't turn the wheel counterclockwise. And if you release the lock to try it anyway, the spring will move faster.

To count the clicks - each click further tensions the spring - you need a reference point for the start.

For this, the lower end of the spring must rest against a pin against which it is tensioned. Here for the opening curtain C1.

To better observe the spring end on the pin for C2, I removed the protective cover for the two magnets. It's just clipped in place.

Here you can see the spring end and pin for C2, the closing curtain.


For an initial measurement, I turned both wheels 30 clicks further and determined the curtain travel times on the camera tester. I then estimated the corrections for both curtains in clicks and worked my way up to the target time of 7.2 milliseconds.

With two volts, the magnets hold their armatures reliably.

Connection to the shutter board.

Measuring the curtain travel times on the camera tester.

With this nice result, I finished the settings. This means I'm almost at the target time of 7.2 milliseconds.

I'll check tomorrow morning whether these times hold for C1 and C2.

If everything's OK, I'll reassemble the 7000 and measure the shutter speeds as well.


+++

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

 

[Andreas Thaler]

The curtains spring tensions have not changed overnight; the values for C1 and C2 are still within the specified range, meaning the two curtains are moving almost synchronously. Therefore exposure deviations should no longer occur, especially at fast shutter speeds.

And since the target speed of 7.2 milliseconds has been reached, the exposure times should also be as expected.

I re-soldered the red positive cable; it was loose. If it comes off during assembly, the camera would have to be disassembled again.


I'm curious to see if everything fits after assembly

 

[Andreas Thaler]

Minolta 7000 AF: Electronic Troubleshooting, assembly successful, shutter now works precisely

After assembling and testing the 7000 AF, I discovered that some camera functions were unavailable:

• The AF wasn't working,
• the corresponding LEDs in the viewfinder weren't lit, and
• the aperture values weren't displayed on either of the LCDs.
• Furthermore, the aperture always closed to its smallest value.

Since the camera worked before I removed the shutter, it could only be a mistake I made during assembly. Clearly, there was a problem with the signal transmission. And the aperture magnet had also failed.

After inspecting the circuit board as closely as possible with a magnifying glass, I consulted the C & C Troubleshooting Guide for the Minolta 7000 AF.

The problem pattern was familiar; the instructions stated that I should measure the signal waveforms on the five lens pins at the top of the camera bayonet.

What I measured didn't meet the specifications, with some distortions or implausible curves on the oscilloscope.

Beforehand, I examined another part of the circuit as instructed.

So I followed the advice to check the board connection above the prism. I was actually having trouble soldering there, and the upper board was difficult to fit.

After I redid the soldering, all problems were resolved. The aperture also worked as it should

The 7000 can also be triggered without the top cover.

To do this, the contacts of the main switch are bridged with jumper wire. The camera is now ON.

If something doesn't work, you don't have to de(install) the top cover and can start troubleshooting straight away.


Testing the shutter

Now I was finally able to test the shutter, whose curtain travel times I had adjusted.

And the results are a great start to the weekend.

The shutter now works precisely, with even exposure of the image field and correct shutter speeds

The images show the measured result for 1/2000 second, the fastest shutter speed on the 7000 AF.

Both curtains (C1, C2) move at almost the same speed; you can also see how the three sensors on the camera tester are exposed for different lengths.

The center sensor is the shortest, while those above and below are almost the same length, which results from the acceleration and deceleration of the two curtains. Nevertheless, a uniform exposure is achieved, as the EV value indicates.

After completing the assembly, I tested the 1/2000 second again and almost hit the bull's eye with a difference of only 0.02 milliseconds (or 20 microseconds) in the curtain runtime

1/500 s

1/60 s

This allowed me to improve the shutter from +1 EV deviation at +1/2000 second to +0.04 EV as the best value.

Mission accomplished


+++

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

 

[Andreas Thaler]

It got exciting again

When I removed the top cover to attach an adhesive strip to the circuit board, the same error occurred again. Partial camera failure.

So I went back to troubleshooting, re-soldered the circuit board connection, and checked it. Then it worked again until I put the top cover back on. The LCD display was flickering, which meant there was a loose connection.

I finally found the problem when I pulled the smaller soldered circuit board (white arrow in the picture) out from under another one.

A 100 ohm SMD resistor had detached from the circuit board with one lead; it was only visible under high magnification.

That explained the problem. When pressure was applied through the top cover, the connection became unstable.

I scraped off some of the circuit board seal and re-soldered one end of the resistor.

That fixed it.

This means I can finally take photos with this 7000 AF that I had worked on for many hours

END