Canon T90: Cleaning the mirror magnet

Andreas Thaler · Jul 1, 2024

I have a T90 here whose mirror magnet no longer works.

The usual symptom of a quiet clicking sound and a flashing arrow in the display occurs.

The recommended cure of removing the front cover and activating the - easily accessible - magnet with a magnetized screwdriver tip works with patience, but a few days later the problem is back.

So I'm going to remove the magnet from a T90, which in turn has problems with its shutter magnets that I can't solve. And then use this magnet as a replacement.

Fortunately, there are already directions for this project:

Canon T90: Replacing the mirror magnet

The mirror of one of my T90s didn't want to move. The symptom is well known: When you press the shutter button, an arrow flashes in the display and you hear a quiet ticking sound. Otherwise the camera remains still. I opened the camera and tapped the mirror magnet with a magnetized...

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The project starts soon

MFstooges · Jul 1, 2024

My head spins just to learn how many magnets are in there. Is this normal for motorized AF bodies of any brand?

Andreas Thaler · Jul 1, 2024

MFstooges said:
My head spins just to learn how many magnets are in there. Is this normal for motorized AF bodies of any brand?

I suspect there are a total of four magnets in the T90, which is an MF camera by the way

La Canon T90

La canon T90, l'ultima ammiraglia FD. Febbraio 1986, Canon lancia sul mercato la T90: era estremamente innovativa e nel cont...

sistemacanonfd-blogspot-com.translate.goog

(Google translation Italian > English)

Andreas Thaler · Jul 4, 2024

When I remove the mirror magnet from the donor T90, I also take the opportunity to see how to get to the shutter. The shutter magnets on the donor camera are obviously defective (EEE, HELP).

The way there leads through layers of flexible circuit boards. There should be instructions for this in an issue of the SPT Journal on the T90.

This is just experimental, as I don't have any replacement magnets and assume that the disassembly/assembly is too complex and will not be carried out without damage.

I think it's hopeless to repair/refresh the defective magnets. But I can look into it, maybe I'll come up with new findings.

Andreas Thaler · Jul 5, 2024

Today I removed the mirror magnet from an abandoned T90 as a replacement and practiced the process.

It wasn't easy because I first had to find out at what angle I had to push the magnet back into its holder. It's very tight there.

Andreas Thaler · Jul 5, 2024

A cleaning attempt

Now I was ready to replace the magnet on my T90, which was no longer working.

But first I wanted to try whether cleaning the magnet would make it work again.

Andreas Thaler · Jul 5, 2024

Dismantling the battery compartment and front panel

The leatherette on the bottom of the battery compartment is self-adhesive and can be removed.

Three pairs of screws (the holes for the one on the left are not visible here) and the golden retaining ring in the middle must be loosened.

The compass tool in use.

The leatherette on the handle is lifted at the bottom to release the battery compartment.

Now the battery compartment can be removed. Be careful not to loosen the soldered wires.

The two screws on the locking mechanism of the backdoor are only slightly loosened.

In order to be able to lift the loosened plate more easily in the next step (taking off the front panel), I remove the backdoor.

Three retaining screws.

The front panel can now be removed.

Documentation of the cable connections in case a cable comes loose during work and needs to be re-soldered.

The ground cable on the battery compartment is disconnected; I will solder it back on later.

Removing and cleaning the mirror magnet

Here is the mirror magnet.

Due to space constraints, the narrow screwdriver blade has to be placed at an oblique angle to get to the screw head fixing the magnet on its mounting plate.

After a few attempts, it is possible to loosen the screw, which is secured with soft sealing wax.

Andreas Thaler · Jul 5, 2024

The sealing wax holds the magnet on its mounting plate.

Using the screwdriver blade, the magnet can be carefully pried off its mounting plate.

With the probe, I pull the magnet upwards at an angle.

Done

The magnet is now only connected to the housing with its two connecting cables.

The contact surfaces of the magnet, which consists of three parts.

The coils magnetize or demagnetize the two parts underneath. The third part, which opens and closes with the other two parts, is located in the housing.

I cannot determine whether all parts are magnetic or just one or two.

In any case, when current flows through the coils, a magnetic field is created that opens or closes the contact. This depends on the circuit of the magnet, which I do not know.

Using electronics cleaner and a cleaning swab, I clean all three contact surfaces of the magnet.

The magnet is back in place and screwed tight.

Soldering work

Re-soldering the ground cable to the battery compartment.

The soldering point of the yellow cable on the circuit board is no longer solid. I am therefore re-soldering it.

I use plenty of flux for all soldering work with existing solder.

Andreas Thaler · Jul 5, 2024

Test with batteries - the mirror moves again

Reassembly

Coupling the stop down slider on the front panel with its counterpart (the picture shows another T90).

The front panel must be inserted precisely.

The front panel is inserted under the retaining plate of the backdoor lock.

Testing the stop down slider.

The T90 is back in operation.

Andreas Thaler · Jul 5, 2024

Conclusion

A non-functioning mirror magnet does not necessarily have to be defective and needs to be replaced.
Cleaning it may be enough to get it working again.
Alternatively, you can try the well-known method using the magnetized screwdriver blade to reactivate the magnet. This is less effort.
This also gives hope for the two shutter magnets, although they are installed in such a way that they can only be reached by deeply dismantling the camera. A project that is still pending.

+++

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

Andreas Thaler · Jul 5, 2024

Andreas Thaler said:
The sealing wax holds the magnet on its mounting plate.

The sealing of the screw was probably to hold it in place, as there is some vibration when the trigger is released.

I'll put some nail polish there next time I get a chance.

Andreas Thaler · Jul 9, 2024

The magnet still works perfectly, so I can recommend the cleaning described as a solution.

Andreas Thaler · Jul 9, 2024

An attempt to get the magnet working again with a spray of electronic cleaner while it was still installed was unsuccessful. I probably didn't hit the spot where the magnet makes contact.

But I don't think removing it is critical.

If you can loosen the magnet's retaining screw without removing the battery compartment (the angle for the screwdriver is unfavorable), things are even easier.

Andreas Thaler · Jul 13, 2024

Assumption: Contamination as the cause of the problem

The mirror and shutter have been working perfectly since I cleaned the mirror magnet.

I'm cautiously coming to the conclusion that the problem is not with the three-part magnet, but with dirt on its contact surfaces. I was actually able to remove the deposits when I cleaned it.

The well-known method of activating the magnet using a magnetized screwdriver blade is probably based on briefly changing the magnetic conditions so that the parts can separate.

Dirt is probably sticking the parts together.

Contamination can be seen on the contact surfaces of the magnet.

This theory is supported by the fact that the problem often occurs when the device is not in use for a long time.

I'll try to confirm my theory with another T90 whose mirror does not fold up (ticking noise, arrow flashes on the display).

The same should then also apply to the shutter magnets, which could be cleaned too (shutter does not release, EEE/HELP are displayed).

Then the only remaining problem would be getting to the two magnets.

braxus · Jul 13, 2024

If you had to replace the mirror magnet with a new one, what would you use for its replacement? Would any EOS camera part work for this?

Andreas Thaler · Jul 13, 2024

braxus said:
If you had to replace the mirror magnet with a new one, what would you use for its replacement? Would any EOS camera part work for this?

I would remove a magnet from an abandoned T90.

Whether a magnet from an EOS camera fits depends on its dimensions and electrical values.

I assume that the magnets are not identical.

Andreas Thaler · Jul 31, 2024

Screw on the mirror magnet

The slot in the head of the screw that holds the mirror magnet in place is narrow.

In order to be able to turn the screw, which can only be reached at an angle, safely, I reworked one of my slotted screwdrivers with a corundum grinding tip on the Dremel.

The blade is now narrower and fits.

It takes a certain amount of pressure, and the torque should be constant so that it doesn't slip.

The left-turning screw is sealed with soft varnish which can be replaced with nail polish.

Willy T · Jul 31, 2024

Congratulations again! And with appreciation for the clean clarity and lighting of your process photos. The investment in extra time and effort put into documentation must surely at least double the project overhead.

Andreas Thaler · Jul 31, 2024

Willy T said:
Congratulations again! And with appreciation for the clean clarity and lighting of your process photos. The investment in extra time and effort put into documentation must surely at least double the project overhead.

Thanks! Just a LED work light and an iPhone

mshchem · Jul 31, 2024

Andreas Thaler said:
Thanks! Just a LED work light and an iPhone

Isn't technology wonderful! Here I was thinking you were using bellows and a ring flash I really enjoy looking at your posts!

Andreas Thaler · Aug 1, 2024

mshchem said:
Isn't technology wonderful! Here I was thinking you were using bellows and a ring flash I really enjoy looking at your posts!

Thanks!

Yes, it's an old iPhone 11 Pro Max, the close-up quality is excellent, but sometimes the shutter release and focusing on the spot is acrobatics, you‘d need another hand.

With a table tripod the whole thing becomes too cumbersome.

The images can be quickly optimized on the iPhone, downscaled for the web and uploaded to the forum. I only create my posts with the iPhone.

MFstooges · Aug 1, 2024

I feel like you're soon becoming T90 PhD
I am eagerly waiting when you start to hack the software.

Andreas Thaler · Aug 1, 2024

MFstooges said:
I feel like you're soon becoming T90 PhD
I am eagerly waiting when you start to hack the software.

In truth I have no idea about 99 % of this camera. Least of all about its code

But I am happy to be able to treat the usual ailments to this extent.

We still need a solution for the shutter magnets (HELP, EEE).

MFstooges · Aug 1, 2024

If you make a new magnet will it give you problem when the new magnet is stronger than original part? I am thinking the winding just to give some small "kick" to what is already permanent magnet core and a stronger magnet may cause trouble.

Andreas Thaler · Aug 2, 2024

MFstooges said:
If you make a new magnet will it give you problem when the new magnet is stronger than original part? I am thinking the winding just to give some small "kick" to what is already permanent magnet core and a stronger magnet may cause trouble.

I don't know how the magnets are constructed.

I imagine it like this:

One or two permanent magnets are holding a metal contact.
If current flows through the two coils, the magnetic field of the permanent magnets is canceled and the metal contact is released.
With the mirror magnet, up to now, cleaning the contact surfaces involved was always sufficient when it wasn't working. The shutter magnets at least look similar.
So I suspect that the principle is the same and that dirt is the problem here too.

The two shutter magnets can only be reached after deep disassembly. With the T90, it's a very hard path through the circuit board layers.

Mirror magnet with two coils, the arrow refers to a different context, please ignore.

The counterpart contact cannot be seen here; it is mounted in the camera.

The two shutter magnets as part of the integrated shutter unit.

To the left of the two coils (arrows) you can see the counter contacts, which are attracted by the magnets.

Larry Lyells has covered the Canon T90 in detail in an issue of the SPT Journal.

I'll check to see if I can find anything about the magnets there.

Canon T90: Cleaning the mirror magnet

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