Minolta (Maxxum/Alpha) 7000 AF: Aperture issues resolved/shortcut; LCDs, aperture ring, shutter unit replaced; aperture solenoid cleaned

Andreas Thaler · Jan 29, 2025

Under „Aperture Malfunctions“ in the C & C guide there are instructions to unsolder the white cable to the aperture magnet and then trigger the shutter when the aperture is always open, the LCD displays are correct and the shutter speed is plausible.

The aperture then either closes or it doesn't.

Possible causes of error depend on this.

In my case the aperture remains open.

This eliminates various electronic problems listed.

Three causes:

the magnet does not close or hold - I cannot confirm this as I have direct sight from the outside.
The aperture ring is stuck.
The encoder mechanism is stuck. Here, after turning the motor anti-clockwise (coupling in the base of the camera), the mirror should rise and the aperture ring should rotate freely. It does, but against resistance.

I conclude that I need to remove the mirror box and look at points 2 and 3.

Andreas Thaler · Jan 29, 2025

Here is the mirror box that I removed from my training 7000:

The magnet is closed (blue arrow) and the pawl on the encoder gear is released (white arrow). The aperture can close to the selected value.

The magnet is open and the pawl on the encoder gear is engaged. The aperture is closed to the selected value.

The position of the aperture is determined solely by this mechanism. The further the aperture ring with coupling rotates in the camera bayonet, the smaller the aperture created.

What I am observing now is similar to the Nikon F4, whose aperture is also formed by an encoder mechanism.

If I move the aperture ring quickly back and forth via the coupling, there is a screeching noise.

This is not the case with the training 7000.

That would be an indication that the encoder mechanism needs oil.

This corresponds to the third cause of error in the list above.

Andreas Thaler · Jan 29, 2025

Here you can see the star-shaped encoder in close-up (blue arrow).

It is connected to the gear above and runs through the light barrier of an LED (white arrow). This generates an ON - OFF pulse that will be transmitted to the aperture control.

The encoder tells the aperture control which position the coupled aperture ring is in in the bayonet.

When the selected aperture is reached, the switching magnet opens and transfers the movement to the gear via the pawl, and the encoder with the coupled aperture ring is stopped.

Andreas Thaler · Jan 29, 2025

After removing the mirror box, I will compare the two directly and observe the encoder mechanisms.

However, the transmission from the encoder to the aperture ring runs via a mechanism under the bayonet (white arrows).

I would have to dismantle it here and that will be a difficult mission, as the aperture mechanism also has to be removed.

But let's see what happens.

Stay tuned!

+++

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

Andreas Thaler · Jan 30, 2025

Assumption of how the aperture setting works via the encoder - not verified

I explain the problem like this:

In this case - aperture always open regardless which aperture value is set - it seems that the encoder wheel is running too slowly due to a lack of lubrication. And therefore generates a pulse that does not match the set aperture.

However, the pulse determines which aperture is formed. And since larger apertures require more pulse counts, the setting does not work and the aperture remains open.

The motor should always close the aperture at the same speed. The encoder wheel always rotates at the same number of rounds per minute.

Assuming that it takes 1000 pulses per unit of time to create aperture f = 5.6, but the slow encoder wheel only creates 50 pulses, the aperture will remain open because that is the number of pulses for aperture f = 1.7.

The service manual contains information on how the encoder works, I will look into it.

However, for the repair, the only thing that is relevant is whether the encoder wheel runs freely and is therefore sufficiently lubricated.

That is my assumption, which I hope to be able to verify.

ogtronix · Jan 30, 2025

I got a working one of these attached to a mouldy lens. Playing around with bulb mode and detaching the lens after opening the shutter to try wiggle the aperture set ring, my guess is it doesn't bother releasing the electromagnet with no lens attached so the thing can freely rotate?

It's a confusing mechanism. I'm not sure what's decoupling the mechanism from the motor. There's also the chance mine isn't fully working though, I'm not feeling any backlash absorption springiness...

Like what's this part all about? What's "Disengaged by forward running" mean? I'd assume the motor can't operate in both directions since it's attached to the film... but then again that'll have a slip clutch built in, so maybe it does reverse?

Andreas Thaler · Jan 30, 2025

ogtronix said:
Playing around with bulb mode and detaching the lens after opening the shutter to try wiggle the aperture set ring, my guess is it doesn't bother releasing the electromagnet with no lens attached so the thing can freely rotate?

Yes, I observed this with a functioning 7000.

When the shutter is released without the lens attached, the ring with the aperture coupling rotates.

Andreas Thaler · Jan 30, 2025

Here I have a 7000 that works but the viewfinder display shows almost nothing.

I will examine the display and see what I need to replace or clean, parts are available.

Andreas Thaler · Jan 30, 2025

The fate of many 7000 is probably forgotten and leaking batteries. But thanks to the design of the battery compartment, the battery contacts on the camera are not corroded.

Andreas Thaler · Jan 30, 2025

Andreas Thaler said:
View attachment 389438

Here I have a 7000 that works but the viewfinder display shows almost nothing.

I will examine the display and see what I need to replace or clean, parts are available.

In the service manual, on page 243 (PDF) „Servicing measures against ‚in-finder segments OFF‘“, there is information on the structure of the display unit and instructions on cleaning the contacts.

I suspect that there are contact problems due to oxidation.

I'll take a look at it tomorrow.

Andreas Thaler · Jan 30, 2025

No success in fixing the display problem

I couldn't bring the viewfinder display back to life by cleaning the contacts with isopropyl alcohol; it no longer showed anything.

So I replaced the entire display unit with the one from my spare 7000, which I had previously dismantled and cleaned for practice. But that didn't produce any digits in the viewfinder either. The LCD remains blank.

Either the loosening of the circuit board - LED connection and the cleaning had rendered both display units inoperable, or the control on the camera side is not working.

I don‘t know.

Here are some details:

The display unit of my spare 7000, the cover is missing here.

The clamp and pressure bar have been removed. They press the contacts of the circuit board and LCD together.

The circuit board was partially glued to the LCD contacts. The contacts do not look nice.

After reassembling the display unit on my spare 7000, I swapped it for the patient's. Five cables need to be soldered. The picture shows the faulty display which I exchanged.

In order to be able to trigger the camera even without the main switch, which is located on the removed cover, I bridged the main switch contacts with copper foil.

Conclusion

The cause of the error remains unclear.
Either I damaged both display units by opening and cleaning them or the control by the 7000 is not working.
The contacts on both display units do not look good. Perhaps the bonding has caused corrosion over the decades.
My gut feeling tells me to keep my hands off it, the stuff is brittle.

+++

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

ogtronix · Jan 30, 2025

It's not corrosion it's the old 'anisotropic conductive film' breaking down. Isopropyl alcohol doesn't touch it. What worked for me was acetone, but be careful to keep it off the polarizing films on the LCD itself since it dissolves those.

Andreas Thaler · Jan 30, 2025

ogtronix said:
It's not corrosion it's the old 'anisotropic conductive film' breaking down. Isopropyl alcohol doesn't touch it. What worked for me was acetone, but be careful to keep it off the polarizing films on the LCD itself since it dissolves those.

I'm not familiar with this type of LCD. I have experience with the LCDs of Nikon F3 and F4 with zebra conductive rubbers.

The contacts on the LCD glass look as if they were vapor-deposited. You can scratch them off with the probe.

What kind of technology is that? I'll take another look at your post about the LCD in the 9000.

Andreas Thaler · Jan 30, 2025

In the service manual they use "Frontsolve" for cleaning, but I haven't found any information about it on the web.

Andreas Thaler · Jan 30, 2025

The replacement of parts with those of different dimensions is also described.

For this, parts of the display unit obviously have to be reinforced with adhesive. The obvious aim of the replacement is to create a stronger pressure on the circuit board - LCD contacts.

It ends with:

My reading of this is that if the repair attempt is unsuccessful, either a large part of the circuit board (PCB-A) or the entire display unit must be replaced.

All very interesting. I tried to take the display unit apart, but everything is glued together except for the plastic cover with the magnifying glass for illuminating the display. Where is the LED for the illumination?

It's a devilish thing!

Andreas Thaler · Jan 30, 2025

I won't try anything else here, as I went over all the contacts with an eraser and fine sandpaper as a last resort. To no avail. But I've been warned for the next repair.

@ogtronix

Thanks!

Andreas Thaler · Jan 31, 2025

Display unit successfully replaced

Now it worked after all

I took the display unit from another spare 7000 and inserted it into my patient.

The process:

Cleaning the faulty display with acetone. I wasn't sure whether the glass should be free or whether the existing residue was necessary for the contact. So I only cleaned it superficially. That at least brought a few digits onto the LCD.

To make sure that the display unit was being controlled by the 7000, I used an oscilloscope to measure some contacts on the circuit board for the display unit. Regular square wave signals were visible, so I assumed that it was OK.

Then I installed a display unit from a spare 7000 into the patient. Again, only a few digits were displayed, even though the display unit on the spare 7000 was working perfectly.

I then cleaned the display glass thoroughly with acetone and isopropyl alcohol until it was shiny.

I also cleaned the contacts on the board with acetone and isopropyl alcohol.

Parts of the LCD display were now shown correctly.

By moving the contacts with the retaining clip inserted, I was able to completely restore the display.

Conclusion

Thanks to @ogtronix tip about cleaning the display glass with acetone, the replacement was successful.
The glass must be completely cleaned of all residue, as must the contacts on the circuit board.
To display all digits, the contacts on the circuit board can be moved on the already installed display unit.

+++

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

Andreas Thaler · Jan 31, 2025

Putting the top cover back on

was a struggle that lasted for hours.

Due to the cover’s pressure on the circuit board contacts to the display, the symbols for the operating modes on the left were not displayed.

It was a matter of a fraction of a millimeter.

I changed the position of the contacts on the display unit and pushed a spacer made of insulating tape under the circuit board contacts.

I previously replaced the original masking tape, which insulates the contacts on the circuit board from the flash contacts in the top cover, with insulating tape.

After many attempts with the cover up and down, adjustments and battery holder on and off, cables that went off etc. it worked and the display now shows all the digits in full.

It was a tough tour with lots of ups and downs and some bad curses

Yesterday evening and part of the night and today straight after an early breakfast back at the table.

You shouldn't work when you're overtired, but I was able to cross the finish line

+++

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

Andreas Thaler · Jan 31, 2025

Andreas Thaler said:
Where is the LED for the illumination?

Here are the three amber LEDs, directly below the LCD.

Andreas Thaler · Jan 31, 2025

I'm now wondering where the residue on the display glass comes from.

Was it a material for better contact that disintegrated, as @ogtronix suggested?

But what was the point of that if it can be done without, as can be seen after cleaning the LCD glass?

ogtronix · Jan 31, 2025

Andreas Thaler said:
I'm not familiar with this type of LCD. I have experience with the LCDs of Nikon F3 and F4 with zebra conductive rubbers.

The contacts on the LCD glass look as if they were vapor-deposited. You can scratch them off with the probe.

What kind of technology is that? I'll take another look at your post about the LCD in the 9000.

The coating on the glass is indium tin oxide, a transparent conductor that's as far as i'm aware used on every type of LCD, as well as other types of display. It's impossible to solder to, so there's a few different technologies to connect PCB pads to it - such as the zebra strips. In the case of that LCD it's using anisotropic conductive film: https://en.wikipedia.org/wiki/Anisotropic_conductive_film

You can't easily replace the original anisotropic conductive film connection at home since it generally requires a heated press calibrated for the job, on top of the film being hard to source in small quantities. But you can attempt to re-adhere them with a little heat and pressure, like in this video but I never had any success trying that in other devices.

My horrible post in this thread covers replacing the conductive adhesive with a zebra strip, which is what the service manual recommends as the repair, along with epoxy adhesive on the retaining bar to hold everything more securely once connected.

Minolta (Maxxum) 9000 AF: Dissection and investigating the aperture issue

One question though, these were also known for having leaking LCD windows. Can they not make these leak proof? This problem also affects The Nikon F4 as well and I had to stop using one because the LCD went blank after a few years in my use. With the F4 you can replace the LCDs quite easily...

www.photrio.com

Andreas Thaler · Jan 31, 2025

Structure of the display unit of the Minolta 7000 AF - a technical work of art

I have never seen such a complex electro-optical structure in a small format.

Combined diffuser/magnification bar made of transparent plastic, removed.

On the left a diffuser for illuminating the display with daylight, below three amber-colored miniature LEDs for artificial lighting, which switches on automatically.

The mini magnifiers on the right are probably used to reflect the miniature LEDs for AF (3) and flash readiness (1). This increases the brightness of the display, which is guided into the viewfinder via two mirrors.

The socket for the LEDs has been removed. Above that is the LCD with a polarizing filter film.

The LCD removed.

Mirror one …

… and two.

An incredible construction.

Andreas Thaler · Jan 31, 2025

ogtronix said:
You can't easily replace the original anisotropic conductive film connection at home since it generally requires a heated press calibrated for the job, on top of the film being hard to source in small quantities. But you can attempt to re-adhere them with a little heat and pressure, like in this video but I never had any success trying that in other devices.

Then I must have just pulled off a trick.

I simply removed the remaining coating on the LCD and connected it directly to the circuit board. And it works perfectly.

ogtronix · Jan 31, 2025

Andreas Thaler said:
Then I must have just pulled off a trick.

I simply removed the remaining coating on the LCD and connected it directly to the circuit board. And it works perfectly.

I'm not really sure why LCDs never seem to be connected with the gold contacts directly against to the ITO traces. Regular stiff PCBs won't be flat enough and you'd be stressing the glass to try press them together, so it makes sense to use something flexible there. But here maybe the conductive bond is more about making the assembly consistent and easy.

Either way you've absolutely improved it from where it was!

Andreas Thaler · Jan 31, 2025

ogtronix said:
Either way you've absolutely improved it from where it was!

But if I were a service technician at Minolta, they would have thrown me out today because I needed a total of three display units for the repair, two of which were disassembled!

Lucky for 2025 is the person who has spare parts cameras and does this just for fun

I also replaced the top cover and the handle because I had damaged both.

I can only remember what I did with each camera by looking at the serial numbers, my repair log and of course my reports here, which I also write for myself.

Minolta (Maxxum/Alpha) 7000 AF: Aperture issues resolved/shortcut; LCDs, aperture ring, shutter unit replaced; aperture solenoid cleaned

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