Minolta Dynax 7000i: Removal of mirror box and shutter, cleaning the shutter magnets brought back the short shutter speeds

The Minolta (Maxxum) Dynax 7000i (Minolta Alpha 7700i) was the successor to the Minolta (Maxxum, Alpha) 7000 AF and was released in 1988.

The 7000 AF was the first SLR with integrated autofocus, which was a huge market success and ushered in the era of automatic focusing in SLR cameras.

The 7000i offers faster "intelligent" autofocus, multi-segment metering, and introduced the Minolta chip card system, which programmed the camera to expose specific subjects. For example, "Travel" with depth-of-field priority or "Portrait" with appropriate aperture priority for background resolution.

It's a heavy, solid and well made camera that can be acquired very inexpensively on the used market.

I just have managed to get three defective 7000i practically for free

I plan to open and examine one of them, following the instructions in the SPT Journal January/February 1991:


A Minolta Service Manual seems not to be available.

I'm particularly interested in the extent to which the 7000i can still be DIY repaired and how the internals differ from the Minolta 7000.

I suspect that with the 7000i I am going to reach the limit of repairability, which I originally set with the Minolta 9000 AF. But I'm open to surprises.
I still also assume that it's not the integrated circuits that are failing, but the peripherals, i.e., contacts, connections and mechanical parts.

Here, too, we are breaking new ground, at least as far as repair reports on the web go. I haven't found anything on this except @ogtronix teardown at



I'm curious to see how the expedition goes

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I thought my knowledge of its predecessor, the Minolta 7000 AF, would give me a head start, but that's not the case.

While the 7000i has similar components and technologies, it's, of course, a new class of camera.

The electronics are more advanced, but there are still interesting connections with the mechanics that make DIY possible and interesting.

I need to prepare thoroughly for this project, which will take some time.

A closer look

Since the 7000i is new to me, I took a closer look at both I own today, familiarized myself with how to use them, and put them on the Reveni Labs Camera Tester.

I am switching to the 7000i as a Minolta 7000 AF user.






While the 7000 AF features an amber illuminated viewfinder display, the 7000i boasts a bright green color plus an additional illumination for the main LCD. The viewfinder features LEDs for AF and flash.

As with the 7000 AF, the display is extensive on both LCDs.








A special feature are optional chip cards, which allow the 7000i's settings to be automatically optimized for specific subjects.

This card is the Portrait card, which favors large apertures.

The golden contacts still need a thorough cleaning, including those in the camera.






The card is inserted into the side flap …




… and can be switched on and off.

A revolutionary thing in 1988 that turned snappers into professionals and took work away from professionals - if they wanted it …


It turned out that one of the 7000i

has a problem with the shutter. The camera couldn't even build the medium shutter speeds, but otherwise everything worked fine.

Ideal for a first attempt at repair!


Candidate number two works perfectly

Here are the results on the camera tester for the shortest 1/4000 second.

The distance between the curtain travel times decreased after a few shots and thus also the exposure deviation in the image.

Apparently the camera hasn't been used for a long time.


Shutter test

The measurement is carried out using three sensors.

The camera tester offers four displays for a measurement result:




1/4000 s: Curtain travel times for the opening (C1) and closing (C2) shutter.

Above are the shutter speeds measured per sensor in milliseconds.

5.5 ms is the target curtains travel time following Larry Lyells in the SPT Journal. The result is close.




The shutter speeds shown as usual fractions, below the exposure deviation in the image shown as exposure value (EV).

You can see how the shutter curtains accelerate and decelerate. The exposure error is acceptable and decreases steadily toward longer shutter speeds.




Here the exposure deviation is displayed for the upper and lower sensors, while the measured shutter speed for the middle sensor is displayed in milliseconds. Below that, the curtain travel times.




In the first quadrant at the top left, the acceleration of the shutter curtains is shown in millimeters per millisecond.

Quadrants 2 to 4 show the opening and closing times of the shutter curtains per sensor. In the middle sensor, the first shutter curtain opens the slit after 1.91 ms, and the second shutter curtain closes it after 2.09 ms.

This gives an idea of the uniformity of the exposure slit as it speeds across the image.


Exposure test



Exposure test with a Minolta AF 50/1.7 lens attached at EV (exposure value) 15 and ISO 100.

The camera tester determines whether the 7000i sets a correct shutter speed/aperture combination for this brightness and at this assumed film speed.

It does, here in program mode. The target and actual values are identical, with no deviation in EV.




The diagram shows the exposure process.

The horizontal axis represents time, the vertical axis represents exposure.

It can be seen that the process is smooth.

What's going on with the tail on the right is interesting. The exposure should have already ended. I'm hoping the shutter isn't slowing down when closing.


Motor speed test



The camera tester can also determine the frame rate in continuous mode.

The 7000i manages 3 frames per second (FPS) with new batteries at 1/4000 s and AF disabled.

Aperture test

The exposure test with a lens is only meaningful if the lens forms the apertures correctly. However, it's also helpful to know how the lens stops down.

My test candiate here is the Minolta AF 50/1.7 just used on the 7000i.




At full aperture, i.e., when the aperture blades are not visible, the measured aperture corresponds to the nominal value of the lens. Here, it is f = 1.7.




At the middle aperture of f = 5.6, this is no longer so nice; the lens only reaches f = 4.9, which means it overexposes.

However, the deviation is only small.

Conclusion

• The camera tester gives a good idea of the camera's performance.
• Even if there are deviations, they aren't significant in practice with negative film.
• So, it wouldn't make sense to disassemble the 7000i or the 50/1.7 just to achieve getting minor better results.
• In the case of the first 7000i, however, the shutter isn't working, and I'll try to see if I can fix that.
• Overall, the 7000i is an impressive development of the 7000 AF. It feels great in the hand, is quiet, and gives a high-quality, solid impression. I'm curious to see what it looks like inside

+++

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

Hello Andreas,

I offer one item on ebay https://www.ebay.de/itm/145237524315 - and untill today no one wants to buy it.
Do you?

forest bagger said:

Hello Andreas,

I offer one item on ebay https://www.ebay.de/itm/145237524315 - and untill today no one wants to buy it.
Do you?

Click to expand...

Sold!

Why didn't anyone want the 7000i?

Probably the usual „plastic camera“ verdict again.

I'll counter that with pictures when I open the camera and try to fix the shutter.

There's nothing cheap or inferior about it; the thing is solid and well-thought-out

Hello Andreas!

Andreas Thaler said:

Why didn't anyone want the 7000i?

Click to expand...

I don't know - maybe because the broken plastic on the grip?

forest bagger said:

Hello Andreas!
I don't know - maybe because the broken plastic on the grip?

Click to expand...

In the best case

I almost forgot:

The 7000i has a red AF-assist illuminator on board. This allows the camera to focus in the dark and on monochrome surfaces by projecting a striped pattern for the AF.

This was previously only possible in combination with an external flash.

Yes, the 1980s were an exciting time in 35mm photography

It turned out that one of the 7000i

has a problem with the shutter. The camera couldn't even build the medium shutter speeds, but otherwise everything worked fine.

Ideal for a first attempt at repair!

Click to expand...

In the SPT Journal, Larry Lyells provides detailed troubleshooting information.

Regarding this error:



I suspect the magnet because the camera was used for a long time by the previous owner and it is unlikely that the solder joints will dissolve or the IC will become defective.

Since I can't find the Minolta Service Manual for the 7000i, I'm using the one for the largely identical 8000i as a guide.

Unfortunately, this edition doesn't include instructions for removing the mirror box/shutter, nor does it have a troubleshooting section. The information in the SPT Journal is helpful here.

The circuitry of the 7000i is more advanced and therefore more complex than that of the 7000 AF.

Digital technology enables advanced functions and calculations and is housed in integrated circuits.
As with the 7000 AF, there are block diagrams that provide information about the individual functional groups of the circuit (SPT Journal). What happens inside the integrated circuits remains unknown.




This isn't important for repair purposes; the only thing that matters here is that the individual electronic components function, especially their connections.
Nevertheless, you shouldn't give up and can try to understand the basics of such circuits. Then you can get an idea of how such microprocessor-controlled camera circuits work.

Anyone interested in this only needs minimal knowledge of analog electronics: voltage, resistance, current, the transistor as a switch, power supply.
Digital electronics, which deals with binary switching processes and even computers, builds on this.

I would like to encourage anyone who is interested in repairing newer cameras to also delve into this area of electronics.
What may seem confusing and dryly abstract becomes understandable if you approach it step by step.
At least then you'll know a little more and won't just shrug your shoulders when you remove the top cover from a camera like the 7000i.

I've found that older textbooks present the field of Digital electronics very clearly. Of course, this isn't state of the art, but the fundamentals remain the same.

This is one of these older basic books in German:


Such books are available for little money and I suspect that the English-language offering is larger than the German one.

Andreas Thaler said:

I suspect that with the 7000i I am going to reach the limit of repairability, which I originally set with the Minolta 9000 AF.

Click to expand...

Pages 1 and 2 of the SPT Journal confirm this assumption:





Here you can see from the entries with ** that special test equipment from Minolta is required for the setting, which is not available.

With a newer version of the circuit board, this also includes setting the fastest shutter speed of 1/4000 second (see *).
This means that the shutter can only be adjusted to a limited extent.

You need to know this before you start removing the shutter to adjust it.

The second step in my project is therefore to determine which version of the circuit board is installed in my 7000i.

However, I am not giving up hope right from the start.

After all, the shutter was set at the factory and should remain stable.
The suspected problem with my 7000i is that one of the two shutter magnets is dirty (see above). This results in shutter speeds that are too long above a certain threshold.
This means that removing the shutter and cleaning the magnet from the outside should offer a chance of solving the problem. Even if I can't adjust the shutter.
The 1/4000 second (and the 1/2000s) may then no longer be within the permissible range, but the camera can still be used.

The first step is removing the covers according to the instructions in the SPT Journal.

I believe that cameras like the 7000 AF, 9000 AF, and 7000i cannot be properly serviced without instructions.

Eg. to work on the shutter, the mirror box must be removed. Even with experience, it's hard to know which cables/connections to disconnect and which components to remove.

Even service manuals don't always provide guided disassembly procedures. Therefore, the SPT Journal, with its detailed explanations, is an indispensable resource.
The service manual for the Minolta 9000 AF as an positive exception is exemplary in this regard.

Here, free work with a screwdriver gives way to studying the available documents and working according to instructions.

Andreas Thaler said:

With a newer version of the circuit board, this also includes setting the fastest shutter speed of 1/4000 second (see *). This means that the shutter can only be adjusted to a limited extent.

Click to expand...

However, I don't see any reason why the electronic adjustment of the 1/4000 second since production should have changed.

Rather, I expect (mechanically induced) deviations in the shutter curtain spring tension over the decades. This should be remedied by adjusting the curtain travel times. The target time for this is specified in the SPT Journal.

We'll see.

Andreas Thaler said:

In the SPT Journal, Larry Lyells provides detailed troubleshooting information.

Regarding this error:

View attachment 395600

I suspect the magnet because the camera was used for a long time by the previous owner and it is unlikely that the solder joints will dissolve or the IC will become defective.

Click to expand...

What is behind these errors?



Wiring to shutter block

If the cable is crushed or the solder connection is poor, too little current flows to the magnet's coil. This current must be large enough to create a sufficiently strong magnetic field to cancel out the magnetic field of the permanent magnet holding the armature. This triggers the corresponding shutter curtain. So the magnet acts as an electrical switch.

For this error to happen, the cable would have to have been damaged during production.

Or the camera was opened at some point, damaging the cable in the process. In that case, the camera would not have exposed correctly from the start.

After speaking with the previous owner, I have ruled out the second possibility. I have also ruled out a faulty solder joint. It either works straight away or it doesn't work at all.


IC4

The IC's behavior can be checked with an oscilloscope following these instructions.

Since it's a digital controller, there are only two voltage states: high or low. This can be seen on the oscilloscope as a brief pulse or change from approximately 0 volts to a value significantly higher.

The two shutter magnets are triggered at different intervals to determine the shutter times. The shorter the shutter time, the smaller the time interval. This should also be measurable with the oscilloscope in dual-channel mode.

For the measurements, it should be sufficient to remove the top cover of the 7000i; IC4 and the two connections for the magnet should then be accessible.

I'll take a look at it.


1st-curtain magnet SL1, open or dirty interface

If the contact surfaces of the armature and magnet become dirty, there may be a slight delay when the shutter is released because the contact surfaces stick together. This has an increasing impact on short shutter speeds, as a delay here has a greater proportional impact than for longer shutter speeds.

If the delay is, for example, 1 millisecond, the proportion is greater at 10 ms than at 1000 ms (= 1 second).

In practical terms, this means that the two shutter curtains that form the slit for exposure are not moving exactly at the intended interval.

I consider this to be the most likely error mode, as the contact surfaces of the magnets can become contaminated over decades, for example by minimal evaporation of lubricants in the camera. Cleaning should correct this.

However, if the magnets have changed their properties over time, they are defective.

Solution: Replace the entire shutter unit, because replacing the magnets individually means disassembling the complex shutter control system. I consider this hopeless due to the loss of adjustments. The magnets aren't available as spare parts either.

A 7000i for spare parts can be used to remove the shutter.

---

All of these are assumptions that may or may not be true. They are therefore only working hypotheses for troubleshooting.

What an awesome camera! Makes me want to go back into the 80s. I never expected something like digital card inserts.

loccdor said:

What an awesome camera! Makes me want to go back into the 80s. I never expected something like digital card inserts.

Click to expand...

Minolta was accused of ripping off its customers. These advanced features were later integrated into the camera software.

Disassembly - removal of the covers

I start by removing the covers to get to the connectors of the shutter magnets to check them.

Larry Lyells provides detailed instructions in the SPT Journal.




After removing the battery and the battery cover, I unscrew the bottom plate, 8 screws.




Removing the end plate with back cover latch, 2 screws.






Front cover, 2 screws.






AEL cover, 1 screw.




Grip rubber stopper on the bottom of the handle, 1 screw.






Three screws secure the top cover.

One of them is hidden above the handle accessible via an opening.

To remove it, you'll need a 1.5 mm hex driver with sufficient length.

I had to order it separately from Amazon.




The hotshoe in the top cover is directly connected to the circuit board.




Desolder the black cable and ...




... the board.




The rubber grip cover can't be removed because it's glued on and breaks when you try to remove it. The plastic has become brittle over the decades.

I have to peel off the rubber grip cover piece by piece.






The double-sided adhesive tape underneath can be scraped off.

Soaking with isopropyl alcohol helps.

The handle is clean so far. The fine work will come later, once the shutter has been repaired.

I don't plan on replacing the rubber grip cover. The handle doesn't look bad as it is, and the plastic is sturdy.

(Sorry for the poor image quality in some places. I've now turned off the macro function on my new iPhone.)




Compared to its predecessor, the Minolta 7000 AF, the covers are easy to remove.

Only desoldering the circuit board from the hot shoe in the top cover is a bit tricky, as the cover's rounded shape doesn't sit securely on the table for soldering. It needs to be supported.

There's also some plastic in that area that doesn't tolerate heat.








On the catwalk.

A lot of plastic, everything a bit less premium than on the 7000 AF, but I wouldn't say the quality is any worse.

The construction is sturdy and functional.

I have the first version of the circuit board, recognizable by the green circuit boards attached. This should also allow me to set the 1/4000 second shutter speed using two trim pots.

Good news.

Tomorrow I'll take a look at the terminals for the shutter magnets and IC4, which I hope to find without further disassembly.

Then I'll check the solder terminals on IC4 and try to measure the magnets to get a better idea of the problem. If the magnets resp. SL1 for the front shutter curtain (opener) are fine, it can only be a matter of dirt on their contact surfaces.

To check and fix that, I'll have to remove the mirror box.

So, I still have some work ahead of me

Stay tuned!

Checks

Here again is Larry Lyells' (SPT Journal) troubleshooting guide for the problem with short shutter speeds (which are too long):



Let’s go through the individual points.


Wiring to shutter block



Here's the connection for the white wire that goes to the shutter.

As far as I can see, there's no damage here, and the solder joint also appears clean.

However, most of the cable leading to the shutter isn't visible.

I'll still resolder it.


IC4

I will use the oscilloscope to measure the signal at the white wire terminal, high or low, as soon as the trigger (SW2) is pressed.

If IC4 is defective, the 7000i will go to the spare parts stock.

But I don't think so. Other functions would also no longer work.




Here's the position of IC4; the blue arrow points approximately to pin 23.

I might re-solder here as well, although I don't think it's necessary. Otherwise, the camera would never have produced properly exposed images; I don't think the solder joint has changed since production.

Unlike the white cable, which is flexible, which could potentially affect the solder joint. Although I don't think that's realistic either.


1st-curtain magnet SL1, open or dirty interface




The two connecting wires of SL1, white and red.

They lead to the solenoid coil, which releases its armature as soon as current is interrupted.

If the coil winding is broken, no current can flow, and consequently the armature won't hold. If it is stuck due to contamination by dirt, it does not release.

If it releases only with a delay, this affects the shutter speed. The armature is then not fast enough for the short shutter speeds intervals because it is held in place by contamination.

I believe this is the cause of the problem.


I can test the coil winding with a multimeter (resistance measurement).

To do this, I unsolder the two wires and measure the coil's resistance. According to Larry, it should be 146 ohms.

If the coil winding is broken, it has a high resistance; the multimeter displays the highest possible resistance value.

I can only determine if it's dirty by inspecting it and fixing it on-site. To do this, the shutter must be accessible, which is the case after removing the mirror box.


As I said, these are all assumptions, supported by the information in the SPT Journal. Anyway, how the magnets are actually wired is irrelevant. There's nothing I can do other than clean them.


Good night from Vienna, we continue tomorrow.