Canon T90: Tutorial for DIY service and repair

[Andreas Thaler]

I have gained enough experience in my recent projects to be able to offer a tutorial on standard service for the Canon T90 here on PHOTRIO.

The work I recommend for every T90 (depending on the available equipment) is:

• cleaning the exterior,
• cleaning the contacts of the command wheel,
• cleaning the inside of the eyepiece,
• removing, disassembling, and cleaning the Copal S shutter (sticky damper); advantages and disadvantages shortcut
• adjusting the curtain travel times and the 1/4000 second, as well as the exposure metering (camera tester required),
• avoiding the infamous EEE error during assembly,
• removing and cleaning the battery compartment of battery electrolyte/resolving battery contact problems,
• tips on soldering and special features during disassembly/assembly,
• cleaning the release magnet (infamous blinking arrow on the LCD) and the shutter magnets (EEE error),
• replacing the memory battery,
• checking the DC/DC converter,
• troubleshooting/available technical instructions,
• other

Information about this can be found in my current posts about the T90 but perhaps there is a need for a detailed step-by-step tutorial.

As always:

All information provided without guarantee and use at your own risk

 

[Andreas Thaler]

No wishes, very good, then my contributions cover everything

 

[Andreas Thaler]

I see a vote for a tutorial? Then I have a job

Over the next few days, I'll compile everything I know, along with source information. The whole thing will be a practical project with a defective T90.

We're taking it step by step and considering what we'll do at each stage.

I'm looking forward to.

 

[Andreas Thaler]

We'll start today

From my box of repair candidates, I'll select a T90 that clearly needs work.

This applies to every T90 now, as the shutter has a damper that has become sticky and is impeding the motion of shutter curtains.

We'll check all functions and analyze any error messages such as EEE/HELP, bc, or a flashing arrow on the LCD with the help of the available service documentation and attempt to resolve the underlying problems. We also try to solve other problems that might arise using the service documentation.

Examining cleaning options (very easy on the T90 due to its seamless, angle-free casing) is another step, paying particular attention to the battery compartment and its contacts, which are difficult to reach.

The final step will be testing and adjusting the camera functions (shutter, exposure).

---

This is intended to be a leisurely project with a focus on details and clarity.

Afterward, anyone interested should be able to at least check their T90 for functionality and make decisions regarding further service and repair work. This should also be helpful when purchasing used T90s or when commissioning repair shops.

Discussion and questions are expressly welcome. Also, suggestions for excursions we plan to undertake, if possible.

Have fun working on the most advanced MF SLR!

 

[Fisytails]

As i just commented on your other thread (i hope it was Ok to unearth that?) your work is irreplacable and i will read along to learn more about my new T90 and how to get it running properly!
Thanks!

 

[Andreas Thaler]

As i just commented on your other thread (i hope it was Ok to unearth that?) your work is irreplacable and i will read along to learn more about my new T90 and how to get it running properly!
Thanks!

You are welcome!

 

[Andreas Thaler]

Our candidate for service and repair

Heavily used and neglected …

… the strong brass eyelet for the carrying strap is bent …

… the second eyelet was torn off.

This T90 was subjected to violence.

After inserting the batteries and turning the power switch to ON, the LCD remains blank.

I use electronics cleaner and a cotton swab on a pair of pliers to clean the battery contacts, which are located deep inside the battery compartment.

No success.

I am using the C & C Associates Troubleshooting Guide for the T90 to troubleshoot the problem.

To do this I have to remove the battery holder.

Back door off.

2 screws on the right, 2 screws hidden.

2 screws.

Some of the screws have different lengths and therefore need to be stored in an orderly manner.

Removing the cap on the handle, it is self-adhesive.

The yellow cable for resetting the circuit when inserting the battery holder has come loose.

I turn on the camera and connect the yellow cable to ground to perform the reset. There's no response.

When I accidentally touch the positive terminal of the battery contact with the cable, the T90 wakes up. The LCD displays, and the camera can be triggered. This is unusual.

Even more unusual is that the LCD flashes at a frequency of approximately 0.5 hertz (every two seconds). The display backlight also flashes in time.

I'm checking the user manual to see if this is a regular feature, such as an error message when the internal memory battery is dead. But that's not the case.

 

[Andreas Thaler]

For further troubleshooting I have to remove the top cover to make measurements on IC3 (integrated circuit) under the LCD with the multimeter.

To remove the top cover, the back door locking plate must be lifted slightly to free the front plate. But the bent eyelet blocks the plate.

The pipe wrench is used to straighten the eyelet.

There is an original replacement available, so the marks on the eyelet are irrelevant.

Now the plate can be lifted.

And with that I can remove the front cover, but first I have to loosen three screws.

The cables from the hotshoe to the circuit board have been desoldered and the top cover can be removed.

This is optional as it makes working easier.

The T90 is placed on the small table stand and is connected to the laboratory power supply with 6 volts.

To do this, I first desoldered the battery compartment. This also makes the work easier.

Voltage measurement at a pin on IC3.

The C & C Guide provides detailed instructions for this.

Since the voltage measurement does not yield the desired values, we follow the troubleshooting instructions and continue by checking diode D3.

To do this, it must be desoldered.

D3 is located under the tripod connection, which is screwed off.

Done

In order to be able to measure the SMD diode in the SOT23 package with my component tester, I insert it into an adapter.

This makes measuring much more convenient and quicker.

Previously, I had to solder wires to the component terminals so the tester's spring hooks could grip them. A laborious task.

The diode is fine.

But shouldn't there be a double diode installed, as I discovered in one of my recent T90 repair projects?

Strange, I'm not aware of any changes to the board.

That can only mean that one of the two diodes has failed.

Or is the component tester displaying incorrect information?

To check this, I desolder diode D3 from an abandoned T90 board in the spare parts box.

In fact, the double diode is defective.

The disassembled double diode is detected by the component tester.

I solder this double diode onto the T90 board as a replacement.

 

[Andreas Thaler]

I'm testing the T90.

Now, after applying voltage, the charge motor starts running briefly, and then EEE appears on the LCD.

I'm already familiar with this error pattern.

I mark the screw head positions on the pressure plate of the front connector with black paint (the front connector connects three flexible circuit boards).

Then I try different screw turnings. This should solve any contact problems.

The screws must be tightened to a specific ratio and are sealed at the factory.

Since that doesn't solve the problem, I replace the pressure plate from my spare parts inventory.

That doesn't help either.

As I was reviewing Larry Lyells' troubleshooting guide for the T90 in the SPT Journal, I realized I'd forgotten to solder the white cable to the shutter connector. I removed it when I took off the top cover.

Now, after soldering, the T90 works.

Problems solved.

A faulty double diode and a forgotten cable connection

 

[Andreas Thaler]

Tomorrow we continue

We'll test all functions and then decide whether to remove the sticky damper from the shutter. The rear (first) shutter curtain still looks good, with no sticky residue visible.

Stay tuned, there's still some work to be done!


+++

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

 

[Andreas Thaler]

Testing functions

Most of the T90's camera functions can be tested without the top cover.

Experience shows that all functions work fine then, as they are controlled by the same ICs. However, only the final, complete test with the camera mounted provides certainty.

Without the top cover, it is not possible to test the camera's functionality with a flash unit, highlight/shadow correction, and exposure preview (the latter could be operated electronically without buttons, but I will leave that out here for the reasons mentioned).

The modes can be selected as usual using the push buttons and command wheel.

All settings are displayed on the LCD.

The command wheel is experiencing some interruptions; we'll clean its contacts.

Self-timer and associated LED work.

Aperture function plausible.

ASA/ISO can be set.

The controls under the palm wing work.

The LEDs as well as the bar-type LCD for spot exposure and the frame counter are working, as is the backlight for both LCDs on the T90.

The bloom in the image is caused by the dirty eyepiece, which we will remove and clean.


Performance on the camera tester

Average values from 15 consecutive exposures at 1/4000 of a second.

The curtain travel times are synchronized at 3.20 milliseconds. The target value is 2.7 ms.

This means that the image is evenly exposed and the shutter speeds are shifted toward slower.

But the 1/4000 s is set correctly.

We'll take another look at all the shutter speeds after assembling the T90.

Values from the camera tester's three measuring sensors.

EV (exposure value) deviations of the upper and lower sensors from the middle sensor, which displays the exposure time in milliseconds.

The more familiar fraction can be determined using a simple equation:

1/x = 0.23 ms
x = 1/0.23 ms
x ~ 4348
=> 1/4348 s

Acceleration and throughput times of the two shutter curtains at the three measuring sensors.

Testing the automatic exposure in PROGRAM mode.

The deviation from the target is only +0.3 EV, which is also indicated by the slightly increasing shutter speed/exposure curve.


Conclusion

The shutter and exposure system of the T90 are working well. There are no noticeable deviations in shutter function due to the sticky shutter (hence the continuous shooting).

Therefore, I will not remove the sticky damper on this T90 today, nor will I reset the curtain travel times. I will only do that if I see sticky traces on the shutter curtains or if test shots show any abnormalities.

---

For removing, cleaning and adjusting the vertical focal plane shutter of the T90 see

Canon T90: The infamous HELP/EEE error fixed through guided and systematic troubleshooting

We've discussed the Canon T90, arguably the most complex 35mm camera with MF, several times here. It's encouraging that most of the common problems can be solved DIY, see: https://www.photrio.com/forum/threads/canon-t90-recommendations-and-notes.202884/ However, one problem that means the...

www.photrio.com

---

 

[Andreas Thaler]

We continue by removing and cleaning the eyepiece and command wheel.

We also examine the main switch, which is very dirty.

 

[Andreas Thaler]

Assessment main switch assembly

For thorough cleaning, it would be good to remove the main switch.

I have removed the assembly from a T90 for spare parts to explore its structure.

While all other parts are easy to remove, the plastic main switch is pressed into its contact.

I could only pry it out, which probably wouldn't work without damaging it, and after that, there would likely be problems with the stability of the switch.

One option would be to replace the whole assembly, but that's not necessary here.

I'll clean the outside of the switch.

The important thing is that it makes contact, and that's what it does.

 

[Andreas Thaler]

Cleaning the eyepiece

Dirt of the Decades.

2 screws.

In order to be able to place the screwdriver vertically onto the screw, it is placed behind the circuit board strip.

The flexible circuit boards are very robust, you just have to be careful not to bend them sharply.

The unit with the sensor and its centering device can now be lifted off.

Eyepiece off.

Pay attention to the slats of the eyepiece shutter, unfolded here.

On the prism part, there's dust and some fungus. I see the latter there often.

Dirt in the front, little in the back.

Wet cleaning with lens cleaning fluid.

Clean again.

A few faint scratches on the glass of the eyepiece remain. Although I don't even know if I made them.

However since I have more than enough original spare parts, I'm sometimes careless, which shouldn't be the case

I simply wiped off the fungus with Zeiss lens cleaning fluid. The glass shows no signs of etching.

I cleaned the plastic eyepiece frame with isopropyl alcohol, distilled water, cleaning swabs, and a microfiber cloth.

 

[Andreas Thaler]

Assembled


Removing and cleaning the command wheel

3 screws.

The wires of the trigger unit are located in their own guide and are fixed with adhesive.

In order to be able to completely remove the trigger unit with the command wheel, I desolder the six wires.

The unit and cables can then be pulled out of the handle.

Watch out for this spiral spring.

The advantage of complete disassembly is that the connections of the fine cables are not subjected to tension and come off.

It also works with soldered cables, but then you have to be careful not to put any strain on the soldering points when the trigger unit is hanging freely from them.

Some dirt accumulated here.

Apply electronic cleaner to all contacts and move them, turn the command wheel several times back and forth.

 

[Andreas Thaler]

I cleaned everything with isopropyl alcohol, distilled water, cleaning swabs, and a microfiber cloth.

We'll install the trigger unit later, but first we'll take a look at the spot underneath


Where the strap eyelet is torn out

Here I've already removed the unit.

On the left is the spot where the plastic eyelet was.

Nothing here can be repaired anymore.

Replacement from a T90 for spare parts is already available.

The gold plated contacts on the motor board.

Cleaning contacts, wipers and the three black metal contacts in the elongated rubber holder with electronic cleaner.

The palm wing as well its surrounding is also cleaned.

The replacement is assembled.

Installing the coil spring in the palm wing is, as always, a test of patience

 

[Andreas Thaler]

Replacement of the brass strap eyelet

An original spare part can be found again in an abandoned T90.

For assembly, the upper circuit board must be desoldered.

The plastic thread no longer holds the screw. This was probably due to the force exerted (leverage effect) on the eyelet.

I glue it in with Loctite.

The circuit board is back in place, all fixations and cables are screwed in and soldered.


Cleaning inside and out including contacts

Isopropanol, distilled water and electronic cleaner.


Replacing, disassembling and cleaning the battery compartment

On the right, fresher replacement from stock.

The T90's battery compartment is always dirty. It's difficult to clean the inner and the battery contacts from the outside.

Therefore, I disassemble the battery compartment for a thorough cleaning.

 

[Andreas Thaler]

SW3. Reset switch in battery case,
yellow wire, Fig. 25. Closes when
you remove the batteries, switching
pin 3 of IC3 low to disable all
operation and reset the circuit.
Opens when you install the battery
holder to enable operation.

Canon T90 Repair Guide

From the Society of Photo-Technologists Journal

learncamerarepair.com

I clean the contacts and the inside of the battery compartment.

Fully assembled.

Test with batteries.

The output voltage can be measured on the red and black battery cables; the battery contacts are OK.


Mounting the battery compartment to the camera

Cables to solder.

This small spring is certainly often overlooked and lost unnoticed.

It lives here.

This is its mating contact.

I haven't been able to figure out what its function is yet. It could be a connection to ground, but I haven't been able to measure it.

 

[Andreas Thaler]

First test with batteries.

Everything works.

Putting on the top cover.

Another Canon T90 has been woken up from its permanent sleep and is ready to work again.

And a carrying strap can also be reinstalled.


The final check on the camera tester shows that shutter speeds from 1/4000 second down are slightly slower than the default as expected. But that doesn't matter as long as the shutter exposes evenly. And it does.

Mission accomplished

 

[Andreas Thaler]

I hope this tutorial served its purpose.

Despite its reputation for being complicated, the Canon T90 is quite easy to service.

You can find more service and repair suggestions here:

Canon T90: EEE error resolved - hint for disassembling/assembling; sticky second shutter curtain; setting the 1/4000 second

In my last two T90 projects, the EEE error appeared after disassembling/assembling the camera. I was now able to determine the cause and fix it. I found the solution, once again, in Larry Lyells' SPT Journal on the Canon T90 🙂 The arrow points to the pressure plate of the front connector...

www.photrio.com

Canon T90: systematic troubleshooting, DC/DC converter replaced, one LED digit missing, sticky shutter, EEE again, summary

Checking a Canon T90 according to the troubleshooting instructions by Larry Lyells in the SPT Journal. https://learncamerarepair.com/product.php?product=1778 No sign of life. Battery compartment removed, measuring the input voltage on the DC/DC converter. Front and top cover...

www.photrio.com

Canon T90: Address unresolved problems; broken plastic parts in Copal S shutter, epoxy, EEE/HELP/bc errors, troubleshooting partially successful

The Canon T90 is particularly fascinating because back in 1986, every available technology was used to create the most complex 35mm SLR without autofocus. Electronically and mechanically, packaged in a stylish and robust housing. Even today, the T90 is satisfactory, but knowing and mastering...

www.photrio.com

Canon T90: The infamous HELP/EEE error fixed through guided and systematic troubleshooting

We've discussed the Canon T90, arguably the most complex 35mm camera with MF, several times here. It's encouraging that most of the common problems can be solved DIY, see: https://www.photrio.com/forum/threads/canon-t90-recommendations-and-notes.202884/ However, one problem that means the...

www.photrio.com

Canon T90: Cleaning the mirror magnet

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...

www.photrio.com

Canon T90: Advanced cleaning of stuck shutter blades

Sticky shutter at EOS Nano Burger gives in „Manage Your EOS Camera’s Sticky Shutter“ https://www.instructables.com/Manage-Your-EOS-Cameras-Sticky-Shutter/ a guide on how to clean stuck shutter blades in a Canon EOS. The reason for the sticking is a small damper under the vertically running...

www.photrio.com

Have fun and success in your work!


+++

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

 

[khh]

Thanks for the guide. I have a Canon T90 that's in pretty good working order, but the command wheel isn't working so well. I'm thinking I should follow this guide and give it a little general CLA while I'm at it.

 

[Andreas Thaler]

Thanks for the guide. I have a Canon T90 that's in pretty good working order, but the command wheel isn't working so well. I'm thinking I should follow this guide and give it a little general CLA while I'm at it.

You can also try to make the contacts conductive again by vigorously rotating the wheel. This should at least improve performance.

 

[Andreas Thaler]

Finally, I would like to encourage anyone interested in repairing and servicing their T90 to attempt to do it themselves. Especially since the T90 is usually not accepted by repair shops, at least that is my experience in Germany and Austria.

The camera is quite easy to disassemble and clearly laid out.

The excellent technical documentation mentioned in the thread - the SPT Journal, the C & C Troubleshooting Guide, and the Canon T90 Service Manual - are available for this purpose and guided troubleshooting.

With a basic knowledge of electronics and camera repair, you can successfully implement this information. Even if it doesn't work out, you'll gain experience, insight, and spare parts.

I still have a few T90s in my box for repairs and will provide updates if I have any news.