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

Andreas Thaler

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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 all of its functions is still a challenge.


The good news

We've discussed Canon's star of the 80s several times here in the repair forum on PHOTRIO and are aware of its weaknesses:
  • EEE/HELP and
  • a flashing arrow on the LCD, which indicates a camera not triggering,
  • a sticky shutter,
  • an adjustment wheel that skips,
  • battery electrolyte deep in the battery compartment,
  • a depleted backup battery or
  • a defective LCD.
The good news is that we now have DIY solutions for all of these problems, which are discussed here.


The even better news

This thread is intended to address problems that occur less frequently and for which there are currently no DIY solutions.

These range from mechanical problems to the bc display on the LCD, which indicates a non-functional camera, to the complete failure of the T90 with no sign of life.

To address these issues, I've collected a few T90s with faults over the past few years.




From the spare parts box


Even some previously hopeless cases from the spare parts box are waiting for a new lease on life. Spare parts are plentiful.


Challenges and fascinating technical details

I'm excited about the challenges of this project and look forward to interesting sessions. The T90 also has fascinating technical details that I'll cover in my repair reports.

The T90 fetches high prices on the used market; even a defective one commands a considerable sum. This shows that the camera is still popular and there's interest in it.

Last but not least, we don't want to discard any more T90s because they've been left with (repairable) defects.

The basis for all repair attempts is again all experience gained so far, the SPT Journal (author: Larry Lyells) and the C & C Associated Troubleshooting Guide as well as the Service Manual for the Canon T90

As always, requests and questions about the project are welcome!

We‘ll start soon.

Stay tuned!
 
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Andreas Thaler

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Never throw away a spare part



If a repair doesn't work, the disappointment is immense.

But before you throw the innocent camera in the trash, put it in a box. On a quiet day, with enough distance, you can sort through valuable spare parts.

Suddenly, you need just that one screw or elastic connector to continue working on another repair project.




Release solenoids, screws and springs of the T90.




Elastic connectors and buttons.




A complete mirror box with the main board, ready for installation. Provided the electronics of the version are compatible.




A tiny ball bearing from the winding mechanism.


Spare parts and complete spare units are also indispensable for study purposes or to try out a repair technique.

So the parts live on.
 
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Andreas Thaler

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Broken worm gear in the shutter mechanism



Here's a Copal S shutter from a T90.

The arrows point to the two worm gears for tensioning the curtain springs. These mechanically adjust the curtain travel times.




This plastic worm gear is intact.







And this is broken. This means the shutter can no longer be adjusted.


See also the posting by @joe_laroids:

Post in thread 'Canon T90 shows the error messages HELP and EEE: Tracking down the last major problem'
https://www.photrio.com/forum/threa...wn-the-last-major-problem.208254/post-2861664
 
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Andreas Thaler

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Some more details



The main circuit board on the prism is somewhat bulky but robust. It is removed with the mirror box, which saves some disassembly work when accessing the mirror box mechanism and shutter.




This tiny red self-timer LED has so much power that its glow is bright and visible. (Left division on the steel ruler: millimeters. Right division: 32 nds.)




Main switch and buttons unit on the back of the T90.




Two metal plates in the grey rubber strip.






When you press the black buttons, the gold-plated contacts underneath close.

The contacts of the slide switch can become dirty, the plastic switch stiff. Electronics cleaner and a little silicone grease can fix this.






These buttons are also available on the top of the T90.
 
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Andreas Thaler

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Replacing the memory battery (if necessary)



The 3 volt lithium battery for holding camera settings when the main batteries are removed is located on the prism.




All of my more than ten T90s have batteries that are still active.




But if a replacement is necessary, it is easily doable.




To expose the battery, I used side cutters to cut the wires all around without desoldering them. Since I no longer need the entire circuit board, this is the destructive but faster way.




The battery is soldered to the circuit board with two soldering lugs.




Desoldering






The soldering lugs are probably spot welded.






For testing purposes, I soft-soldered two tinned copper wires to a larger, used 3 volt lithium battery. The solder points are holding.




The battery voltage is at the terminals, so the solder connection is OK.




The original battery is covered with a thin transparent seal, thus insulating it. I used insulating tape and soldered in the test battery.

Because the battery is too big, I can't fold the circuit board over it.


Now all that remains is to find a lithium battery that matches the dimensions of the original battery,
 
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Andreas Thaler

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Electronic state of the art in the mid-80s




The T90's computer-controlled circuitry is largely housed in ICs.

Here are some of them on the main board.




The silicon measuring cell above the eyepiece for light detection.

Below the eyepiece shutter.




The 7-segment LEDs for displaying exposure values in the viewfinder, among other information.

This power-consuming technology was clearly borrowed from the Canon A-1 from 1978.




All the more interesting is that the viewfinder already incorporates an energy-saving LCD as a successor technology.

Here, the bar display of the spot metering values and the frame counter.




Above is the prism for LCD illumination via ambient light or incandescent lamp.
 
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Andreas Thaler

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After organizing my spare parts inventory for the T90, I'll take a look at the repair candidates. Then it's time to get started.

Stay tuned!


+++

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

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Testing the function of two release magnets



My spare parts stash for the T90 also includes two shutter release magnets, each located on the rewind side of the mirror box.

If the magnet malfunctions, it will indicate a flashing arrow on the main LCD, and the camera won't trigger. This is usually due to dirt or defective coils, as in this case.




The multimeter's crocodile clips grip the two terminals of the connected coils for measurement.




The spec is 67 ohms.

The multimeter, used as an ohmmeter, shows overrange in all positions. This means the coil's resistance is higher than can be measured.




An inspection shows that one of the coils is open, with the wire from the winding broken. Therefore, the coil is high-impedance and the resistance is infinite.

Repair is not possible; this would require soldering the enameld copper wire under a microscope.




The second coil is fine at 64.6 ohms and meets the specification.
 
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Andreas Thaler

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And last, but not least



this is the tiny light bulb that illuminates the two LCDs.

Another old technology that's still in use here, but was later replaced by LEDs.

The bulb has a resistance of 30 ohms, here operated with 2 volts on the laboratory power supply, ~67 milliamperes flow at a power of ~133 milliwatts.


We'll start the project tomorrow, stay tuned!
 
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Andreas Thaler

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One final note:

The usual fix for a stuck release magnet (solenoid) on the T90 is to remove the front cover and touch the solenoid with a magnetized screwdriver while pressing the shutter release.

This can activate the solenoid, but not permanently, as it doesn't solve the problem.

I don't know how the solenoid is wired, but all the ones I've removed and cleaned from the T90 have worked perfectly since then.

So it can only be contamination by dirt.


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Andreas Thaler

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Before we begin, here is master Thomas Tomosy’s assessment of the DIY repairability of the Canon T90:

It is not recommended that you attempt to repair this camera. It is included here only to show what you’re up against when it comes to fully automatic electronic SLRs.
Click to expand...
Thomas Tomosy, Camera Maintenance & Repair, Book 1, Buffalo: Amherst, 1999, Kindle Edition


It's not my place to contradict the master, but I'll allow myself to put things into perspective.

Yes, attempting a repair on your own, without instructions, will probably fail. But with the technical documentation mentioned, especially from Master Larry Lyells in the SPT Journal, it's doable.

Whether it succeeds is another question.

We'll see what happens.
 
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Andreas Thaler

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Candidate #1: A mechanical problem, and once again the shutter that is causing concern

This T90, which came to me with a melted front cover, surprisingly works as expected, but there are problems to be solved.




On the test bench: Clearly used and some dirt.




The aperture lever is bent.

This probably happened when removing the lens.




The mirror needs a thorough cleaning.




Here is an intact aperture hook for reference on a spare parts mirror box.




Removing and replacing the hook would require disassembling the mirror box. I'm not going to do that.




The hook can be adjusted using the curved needle-nose pliers.




The aperture works.


Further checks



The adjustment wheel only reacts to a single click position.




A melted spot on the top cover.




The left mirror box screw is missing.




The mirror shock absorber needs renewal.




Everything on the lower circuit board is in original condition.




The two front mirror box screws are loose.




Everything looks good on the mainboard.




The 3 Volt memory battery still has sufficient voltage.
 
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Andreas Thaler

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Top cover desoldered to be able to work unhindered.


Repair of the adjustment wheel





Rubber grip detached.






The cables to the trigger unit are released from their glued fastening.




3 Screws




The trigger unit can be removed from the handle.

Be careful, though, as it is connected to the cables via six fragile solder joints.




The rotating contact disc of the adjustment wheel with wipers.




A spray of electronic cleaner ...




… and turning the adjustment wheel several times makes the contacts conductive again.






All click positions work again.




At this point, the back of the dial can be cleaned of dust.


This washer …



… is also found in this location on other T90s.

Since it fell off, I'm gluing it in place with Pliobond.


A foam wash for the top cover

 
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Andreas Thaler

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The switches should remain dry, as the contacts underneath are difficult to reach for drying.





Spare parts from stock








An original replacement screw is inserted.




Replacement for the push buttons for mode and exposure metering under the top cover.


Functional test



Since the battery holder is missing, I supply the T90 with 6 volts from the labratory power supply.




All electronic functions are working properly. The red self-timer LED is also active.




Test with lens.


As always the sticky shutter



No T90 is spared.






There are two options for removing the sticky damper residue from the shutter: cleaning it from the outside or removing it.

Since the second option offers no advantage but involves considerably more work and risk, I clean the shutter from the outside.

See also

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


On the camera tester



The two shutter curtains, C1 and C2, move at approximately the same speed, but the curtain travel times are too slow, and so are the shutter speeds.

2.7 milliseconds is the default for both.
 
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Andreas Thaler

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I adjust the shutter from the outside via its two worm gears and see that the screwdriver has worn out the screw head profile. The torque was minimal.

Only with effort and a larger screwdriver can the screw be moved.

Turning the screw caused the second-curtain shutter speed to become unstable. Apparently, one of the plastic worm gears on the shutter was broken.

This is a now known critical weakness of the T90. The plastic breaks.




It's a good thing I have a previously serviced spare shutter from another T90.

Tomorrow, I'll continue replacing the shutter and investigating the defective one.

Stay tuned!


+++

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

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Examination of the removed shutter

I have examined the shutter for the following:
  1. condition of the plastic worm screws for adjusting the curtains travel times,
  2. success of removing the sticky damper from the outside,
  3. effects of removing/cleaning with a pointed probe and acetone.

Condition of the plastic worm screws for adjusting the curtains travel times

I assumed that the worm screw was broken, preventing me from adjusting the tension of the secondary curtain. This is a known issue (see current threads about the T90 on PHOTRIO).




The two plastic worm screws. The top one is for the second shutter curtain, the bottom one for the first.






It is not the worm screw that is broken, but a tooth on the gear.

This meant that the screw could no longer be turned clockwise to increase tension. The curtain became unstable, moving at slightly different speeds as the camera tester revealed.




The cross-head screw profile was completely destroyed by the screwdriver. The torque was low, though.






The worm screws and gears are tightly installed. Replacing them would require disassembling the mechanism, then reassembling and adjusting it.

I don't think that's realistically feasible; anyway, replacements could be printed and installed, see the experience of @joe_laroids:

Post in thread 'Canon T90 shows the error messages HELP and EEE: Tracking down the last major problem'
https://www.photrio.com/forum/threa...wn-the-last-major-problem.208254/post-2861664


Conclusion 1/3
  • The screws have become fragile over the decades. This may be due to the plastic, which has changed its properties, but it may also be due to the fact that the gears are constantly under spring tension.
  • I therefore advise against adjusting the shutter, as this could render it unusable.
  • If adjustments are made, only do so while the shutter is removed, allowing visual inspection and assessment of its condition. However, this would increase the pressure during re-cocking, which could lead to breakage.
  • My experience with several T90s I've had on the camera tester is that the curtains travel times are well synchronized, ensuring consistent exposure throughout the image. The shutter speeds may have shifted toward slower, but that doesn't make much difference.
  • For the reasons mentioned, I don't think it's realistic to replace the plastic parts. But there are other opinions on this, see link above.
 
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Andreas Thaler

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Success of removing the sticky damper from the outside

and

Effects of removing/cleaning with a pointed probe and acetone.


A shortcut for removing the sticky first-curtain damper (located closer to the back of the camera) is a pointed probe and acetone. See also

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

Let’s take a closer look at the removed shutter for this where I used this method today:










Externally everything is clean except for a few sticky residues at the attachment point for the damper and inside the camera under the film window.


A different picture emerges when we disassemble the shutter:













The acetone appears to have dissolved most of the second-curtain damper. Or the damper was already in this state.


Conclusion 2/3 and 3/3
  • Experience shows that the shortcut is effective and makes a T90 with a sticky shutter reusable. However, cleaning from the outside with a pointed probe and acetone is done without sight and therefore not thorough.
  • I therefore recommend removing the shutter for a complete and controlled cleaning. 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
 
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Andreas Thaler

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Tomorrow I'll install the replacement shutter and try to adjust it.

If that works, I can finish the T90.

Every day is exciting and brings new insights

Stay tuned!


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Andreas Thaler

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A radical idea

If the shutter can be adjusted to the target curtains travel time of 2.7 milliseconds, the worm screw and gear could be permanently stabilized with epoxy.

The shutter would then be "frozen" forever and could no longer be adjusted, but that's better than the plastic parts breaking, rendering the shutter unstable.

Of course, this can also be done with a shutter that's already adjusted to an acceptable level. This avoids the risk of moving the plastic worm screw and gear, which could cause them to break.

More on that today.
 
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koraks

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Andreas Thaler said:
If the shutter can be adjusted to the target curtains travel time of 2.7 milliseconds, the worm screw and gear could be permanently stabilized with epoxy.
Click to expand...

Couldn't you glue the worm gear itself? There are really effective epoxy, cyanoacrylate and PU glues that would produce a durable bond even under such demanding conditions.
 
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Andreas Thaler

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koraks said:
Couldn't you glue the worm gear itself? There are really effective epoxy, cyanoacrylate and PU glues that would produce a durable bond even under such demanding conditions.
Click to expand...

The problem is how to remove and reinstall the screw.

The only option I can see is disassembling the mechanism, including the springs. I consider that a hopeless task.

In this case, the screw is intact, but the gear driven by the screw is broken. I don't see any way to repair it.

I'll figure out how to get to the screw later, though, since the shutter is already broken.
 
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Andreas Thaler

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Permanent stabilization of worm screws and gears for adjusting the curtains travel time: Experiment with epoxy

I'll adjust my replacement shutter, which I've already cleaned of the sticky damper, on the camera tester and then permanently bond the screw and the associated gear, both made of plastic, with epoxy.

This should prevent screws and gears from breaking apart and causing the curtain travel times to become misadjusted.

However, the shutter will then no longer be adjustable.

This is an experiment to test this possibility and gain experience.

Action is needed because the T90's Copal S shutters can become unstable on their own due to these breaking parts.






Since I encountered problems when manually triggering the shutter curtains on the camera tester, as I got into the light path to the sensor, I triggered it electronically this time.

To do this, I apply 3 volts to the solenoid terminals via two cables.

First to the first curtain, then to the second. The camera tester then determines the speed of the two curtains, which in this case should be 2.7 milliseconds for both.




This can be easily set up with an adjustable laboratory power supply, cables, crocodile clips and a breadboard.






I insert the shutter into the back of a T90, which I've completely disassembled. This allows me to test the shutter in the camera tester.

Here, I adjust the two curtains using their worm screws.




The shutter is cocked manually.




First test.

The shutter is still within the tolerance of +/- 0.2 milliseconds (ms) between the first and second curtains.

The target time is 2.7 ms.

This makes the shutter too slow; shutter speeds tend to be slower.




I was able to set the curtains close to the target time.




I apply epoxy to worm screws and gears.




Then I cock the shutter and fire to see if the areas under the epoxy move.

This is the case on the left; the spring moves during cocking.

It will be interesting to see what effect this has once the epoxy has dried. To do this, I'll test the curtains travel times again.

If this experiment is unsuccessful, the project will continue with a second replacement shutter. However, I have to remove it first from a spare T90, as I don't know its condition.
 
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Andreas Thaler

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I'd like to point out that this project is primarily about finding solutions, not about repairing a specific T90.

If the two work together, all the better
 
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Andreas Thaler

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The green adhesive on the left side is genuine Canon and presumably also serves to stabilize the worm gears.

But that's not to address a problem with the plastic breaking, but rather with adjustment due to vibration, I assume.

Or it's a seal, as the adhesive offers no resistance when turning the screws.
 
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