Canon T90: HELP and EEE error codes, systematic troubleshooting, disassembling/cleaning the shutter, studying the charge motor and transmission

[Andreas Thaler]

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:

Canon T90: recommendations and notes

Based on my previous (repair) experiences with the Canon T90 with regard to preservation/problems/repair options, I would like to give a summary of the following recommendations/hints: Sticky shutter - gummed-up shutter blades: Can be permanently repaired, damper in the shutter area that has...

www.photrio.com

However, one problem that means the camera will fail completely has yet to be solved:

The blocked shutter with the HELP and EEE error messages in the viewfinder and on the camera's LCD.

We've discussed this at length in this thread without finding a definitive answer:

Canon T90 shows the error messages HELP and EEE: Tracking down the last major problem

One of the most common problems with the T90 is still unsolved: the shutter blocking, accompanied by the messages „HELP“ in the viewfinder and „EEE“ on the display. Until now, I assumed that the cause of this problem was dirty magnets for controlling the shutter. The T90 has two of these...

www.photrio.com

The current state of the discussion is assumimg that the two shutter magnets are dirty and are not firing. Broken plastic shafts in the shutter control could also play a role.


I'd like to restart the topic here from scratch

because, by a stroke of luck, the C & C Electronic Troubleshooting Guide for the T90 is now available, in addition to an excellent article in the SPT Journal and the Canon Repair Manual.

These error messages are dealt with in detail there providing new insights and perspectives for repair.

I'm considering this topic my main repair project for 2025; I have two T90 with this problem to work on in stock.


Highlights to come

• Removing the mirror box to get to the shutter. A particular challenge with the T90 due to the dense installation with flexible circuit boards.
• I also want to explore the T90's setting options; it even has its own built-in test mode.
• The success of these adjustments will be determined again using the Reveni Labs Camera Tester.
• Insights into the interior and technology.
• Advanced tips and hints for DIY work on the T90.

An exciting and long-term project is coming up; we'll start after Easter.

Stay tuned!

 

[Gregory_Nolan]

Great! Looking forward to your repair report.

 

[Andreas Thaler]

Great! Looking forward to your repair report.

Hopefully I won't completely lose my mind dealing with this topic!

 

[Peláez]

It will be interesting to see if he manages to fix the “EEE, HELP” error on the Canon t90 camera, although I fear that those of us who lack the necessary knowledge to undertake such tasks will have to be content with using the camera as a paperweight.

 

[Andreas Thaler]

It will be interesting to see if he manages to fix the “EEE, HELP” error on the Canon t90 camera, although I fear that those of us who lack the necessary knowledge to undertake such tasks will have to be content with using the camera as a paperweight.

I'm starting this project precisely to prevent the T90 from becoming a mere paperweight

As always, I'll aim to structure my corresponding repair report to be as understandable as possible and helpful for DIY projects.

The T90 isn't a magic box either; with the technical documentation mentioned, there's a realistic chance of making progress.

 

[Andreas Thaler]

Our candidate for a repair attempt

• The LCD display is normal.
• The mirror is triggered,
• both shutter curtains don't open,
• EEE appears on the LCD, and HELP appears on the LEDs in the viewfinder.
• After removing/reinserting the battery holder and trying again, the same sequence occurs.

 

[Andreas Thaler]

When troubleshooting, I first refer to the SPT Journal and then to the C & C Associates Troubleshooting Guide.

I follow strictly the instructions and don't go on my own.

Canon T90 Repair Guide

From the Society of Photo-Technologists Journal

learncamerarepair.com

C & C Associates Troubleshooting Guide for the Canon T90

Stay tuned!

 

[Andreas Thaler]

Observations/preparations before starting troubleshooting

• The camera is in very good external condition, there is no visible damage, and it is clean inside and out.
• The main switch has a loose connection, the LCD display is unstable.
• I inserted 4 fresh AA batteries. The open circuit voltage, measured at the battery holder, is 6.54 volts (6 volts is the supply voltage for the T90).
• I cleaned all contacts in the battery holder and battery compartment with electronics cleaner.

 

[Andreas Thaler]

Troubleshooting following the instructions in the SPT Journal

There's a separate section in the SPT Journal for addressing the EEE/HELP error.

Here's a hint for troubleshooting without opening the T90:

I try this several times without a lens attached, but the camera still doesn't work. EEE/HELP continues to appear.

Therefore, we continue with the covers removed to check the solder connections of the shutter-flex connector on the upper circuit board.

I resoldered the indicated solder points on the board, even though they looked normal. However, there was no change in status.

I continue with a voltage measurement on the DC/DC converter, which is located at the bottom of the T90 and provides various voltage levels from the 6 volt battery voltage to power the individual circuit components.

To do this, I have to remove the battery compartment.

Since I have also disconnected the cable connections from the battery compartment to the camera, I connect the T90 to my laboratory power supply.

The circuit can be reset with the yellow cable by shorting to ground, which corresponds to pulling out and reinserting the battery holder, see first troubleshooting instruction above.

On the orange cable, I only measure a maximum of 15 volts after a reset, instead of 18 volts. The voltage drops rapidly afterward. The purple electrolytic capacitor on the DC/DC board is obviously discharging.

It's possible that the capacitor is no longer fully functional. To check and measure it, I have to remove the board.

I perform a few more resets with the yellow wire to ground, and suddenly the shutter fires. Then the T90 goes back into EEE/HELP mode, and after another reset, the camera works. I run the motor in high mode to keep it moving and resolve any contact issues with the magnets.


The solution to the problem came as a surprise

What caused it, and what worked?

I can't say.

• From experience, I know that an EEE/HELP error can sometimes be resolved by triggering the camera. Perhaps it's due to dirty magnets, which then work again.
• Another possibility is that the DC/DC converter isn't providing the required voltage of 18 volts to reliably trigger the shutter magnets; in this case, it's missing 4 volts.
• The electrolytic capacitor might be the culprit; it can no longer be charged to 18 volts. However, I don't have a circuit diagram to investigate this.

Next steps

• I'll continue to shoot the opened camera and observe.
• I might remove the DC/DC converter and measure the electrolytic capacitor. I should have a replacement in my stash. I also have a replacement for the entire converter.
• Then I'll check the loose connection on the main switch.

Stay tuned!


+++

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

 

[Andreas Thaler]

The error occurs again.

The electrolytic capacitor is discharged to ground by the multimeter measurement. Anyway it should start discharging at 18 Volt.

I'm curious to see what the electrolytic capacitor measurement reveals.

 

[Andreas Thaler]

Removing the DC/DC converter, measuring the electrolytic capacitor

The DC/DC converter is housed on a separate circuit board at the bottom of the T90. I removed the converter to be able to measure the electrolytic capacitor.

For testing, I desoldered the electrolytic capacitor from the circuit board.

The nominal capacitance, according to the label, should be 33 microfarads; the tester confirms this value. The ESR value is very good at 0.12 ohms. There's no electrolyte leakage visible at the terminals. There's nothing to indicate a defect.

Before reinstalling the DC/DC converter, I measured the voltage on the converter of another T90. Here, too, the maximum reading was only 15 volts, not 18 volts. This suggests that the converter, including the electrolytic capacitor, is OK.

The converter is back in place, the voltage is correct.


First curtain: Check of the release signal

I check the release signal with the oscilloscope. Everything's OK.

Now it can only be a defective transistor or the magnet for the first shutter curtain.

I've ruled out the transistor; if it were defective, the camera wouldn't have fired in the meantime. I think a loose connection is unlikely.


All that remains is to remove the shutter, test it and clean the magnets.

Before I do that, I'll run

one more test from the C & C Troubleshooting guide.

To do this, I applied the 6-volt supply voltage through a 1-kiloohm resistor to the contact on the shutter magnet and to the orange wire where I had previously measured the voltage.

When I turned on the lab power supply, the camera clicked. When I then reconnected the previous power supply set up, the T90 fired.

That's interesting. Did the previous test revive the magnet? I don't know and will keep an eye on it. If the problem occurs again, we'll take a look at the shutter. Removing it will be quite a job.

It remains exciting

Stay tuned!

 

[Andreas Thaler]

The error reappeared after a rest period of about an hour.

Now it can only be dirty shutter magnets that aren't separating. We'll know more tomorrow.

Good night from Vienna


+++

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

 

[Andreas Thaler]

One T90 abandoned, a second one continues

Today I did the second test according to the C & C guide:

After loosening the front flex connector, the circuit board on the shutter can be accessed.

The green and red arrows point to the connections of the magnet for the front shutter curtain (test points TP-19A and TP-19B). This is where I apply the 6 volt supply voltage.

Both shutter curtains are triggered.

For the second test, I reconnect the power supply to the two battery terminals. To test transistor TR-1, I build a small device with a 1 kiloohm resistor to activate the base (see white arrow in the picture above).

The status remains unchanged.

After reattaching the front plate connector, I test the shutter release. Now the mirror stays down and the curtains don't release. The LCDs shows EEE.

I can't find the cause, so I'm giving up on the T90.

But I still have a T90 with the EEE/HELP error.

It's missing the trigger unit, which I'm replacing with another T90.

The arrow points to the contacts disc and the wipers on the adjustment wheel. This is where misfires due to contamination often occur.

The contacts can't be cleaned from the outside. So I take the opportunity to spray electronics cleaner on the contacts and move the wheel a few times. This activates all the click positions again.

So we can continue hunting

 

[Andreas Thaler]

Next steps

I'll repeat all the tests from the SPT Journal, but I'll skip the ones from the C & C guide, as they would have caused a new problem.

If all tests are OK, I'll continue with the removal of the shutter, and I'll report back from then on. I still believe that dirty magnets are the cause of the EEE/HELP issue.

Stay tuned!


+++

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

 

[Andreas Thaler]

Test results according to SPT Journal (see description above)

• Resets do not resolve EEE/HELP.
• Shutter flex connector: soldering OK
• DC/DC converter: 15 volts on orange wire to ground, OK.
• Electrolytic capacitor, this time measured in circuit installed on the DC/DC converter circuit board, OK.
• First curtain shutter release connection: signal on the oscilloscope OK.

---

This will continue with the removal of the shutter, which I will then test according to the instructions in the SPT Journal. I suspect dirty contact surfaces on the magnets. We'll see.

I'll be back with highlights from the shutter removal.

Stay tuned!

 

[Andreas Thaler]

Highlights removal mirror box and shutter

With Larry Lyells' excellent instructions in the SPT Journal, I made good progress.

There are quite a few connections to be separated, most of them soldered, but relatively few parts to be removed. See the SPT Journal for details.

Flex connector loosened.

Desoldering connections.

Eyelens removed.

Area under the LCD. IC3 from Toshiba.

Shutter connections desoldered.

Mirror box separated with main flex.

Shutter removed.

Details shutter.

 

[Andreas Thaler]

The mirror box is heavy, all-metal, and its mechanics are designed for high performance.

A marvel of Japanese engineering.

Details mirror box.

Main flex on top of mirror box.

 

[Andreas Thaler]

Next steps

Tomorrow (CET) I'll check the shutter unit following Larry's instructions and clean the contact surfaces of the magnets.

If the assembly is successful, we'll see if that has resolved the EEE/HELP issue.

Stay tuned!


+++

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

 

[Andreas Thaler]

Incidentally, this electrolytic capacitor on the DC/DC converter board is also in excellent condition. It almost reaches its nominal capacitance of 33 microfarads, and the ESR resistance is extremely low.

Canon obviously used high-quality capacitors

 

[Andreas Thaler]

It's also possible that the shutter curtains are stuck to the sticky damper on the shutter base. The probe shows that the plastic is already greasy:

I'll see if that's the case tomorrow when I test the shutter.


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

 

[Andreas Thaler]

Removing the sticky damper in the shutter base

Before testing the shutter, I remove the sticky rear curtain damper from the bottom of the shutter. To do this, I open the shutter.

Only one screw needs to be loosened.

The two springs on the right remain in their position.

The damper, a known weak point on the T90.

The camera has obviously not been used for a very long time, as there are no sticky traces on the shutter curtain.

Anchoring on the front. The damper is inserted into both openings.

Remove the damper with the probe. The material is soft and extremely sticky. Clean the tools carefully with acetone.

Fine cleaning with acetone and cleaning swabs.

The small opening on the cover is also cleaned.

The cover is reattached.

Cleaning the opening on the front.

 

[Andreas Thaler]

I'm not installing a replacement for the damper. This corresponds to the status after applying the shortcut with external cleaning, see link above.

I want to leave the shutter in its original condition as much as possible so I can focus on the cause and resolution of the EEE/HELP error.

Since the camera has obviously not been used for a long time, this could have contributed to the magnets not separating.

 

[Andreas Thaler]

How the vertical Copal S focal plane shutter in the T90 works

Shutter cocked

The first shutter curtain is the rear curtain and is released mechanically using the lower release lever (green arrow). The corresponding switch is closed and is connected to ground (green square).

The second curtain is the front curtain and is released mechanically using the upper release lever (red arrow). The corresponding switch is closed and is connected to ground (red square).

Switches in close-up:

• green arrow: first curtain
• red arrow: second curtain

The first shutter curtain (rear), based in the bottom of the housing, closes the film window as being expanded.

The second shutter curtain (front) is compressed in the top of the housing.


Shutter released

The release lever of the first shutter curtain is pulled toward the center of the curtain. The switch opens, and the curtain compresses into the base of the shutter. The film gate is opened.

When the second release lever is pulled, its switch opens, and the curtain expands. The film gate is closed.

When the shutter is electronically triggered, the two permanent magnets open the switches.

Current flows through the coils, which generate a magnetic field and thus cancel out the magnetic field of the permanent magnets.


Testing the magnets

Connecting the laboratory power supply with two crocodile clips.

Setting 3 volt output voltage.

Apply voltage to the two contacts of the first shutter curtain.

The curtain opens.

Apply voltage to the two contacts of the second shutter curtain.

The curtain closes.


Result

The shutter works mechanically and electronically, and is not stuck by remains of the sticky damper.

What I can still do is clean the switch contacts and contact surfaces with electronic cleaner respectively benzine.

 

[Andreas Thaler]

Open the magnet to clean the contact surfaces.

Clean the switches with electronic cleaner.

 

[Andreas Thaler]

Now it's time to assemble the T90.

This requires some preparation and testing to connect the shutter, mirror box, and charge motor.

Stay tuned!


+++

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