Canon T90: recommendations and notes

[Andreas Thaler]

Unless you need 4000 speed? there is very little you can’t do as well or better with the better build, more reliable, lighter, cheaper and more numerous other FD cameras.
No PC port either.

I see

 

[koraks]

People, @Helge in particular, this thread is specifically about the T90 and its maintenance and service requirements. Discussions on which camera is best goes elsewhere. Thanks.

 

[Andreas Thaler]

@koraks Sure, I am sorry.

If we could still find a solution to the T90's inactive shutter magnets, it could theoretically live on forever.

With the T90, current flow through the coil cancels the magnetization and the magnet separates from its armature. Due to long idle times, the magnetic field could no longer have set values.

Since the location in the T90 is very difficult to reach, perhaps a short-term higher current flow through the coils of both magnets could help.

A common solution is to set the camera down hard or treat it with a hammer. This is said to have loosened the magnets in one case or another.

Maybe it's dirt, but the T90s I opened were all clean inside. All that remains is oxidation/corrosion.

I'll take a look at the "current therapy" thing.

Two T90 with HELP/EEE are waiting here for a solution.

 

[Andreas Thaler]

I would like to recommend this Italian site about the Canon FD System including the T90. The most detailed information about the system and camera to date as far as I know, including from a technical point of view.

Already translated into English here via Google Translate:

Il sistema Canon FD

Con questo lavoro ho riportato alla luce lo splendido sistema fotografico che Canon condannò brutalmente all'estinzione nel 1987: Il...

sistemacanonfd-blogspot-com.translate.goog

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

Original versions in Italian language:

Il sistema Canon FD

Con questo lavoro ho riportato alla luce lo splendido sistema fotografico che Canon condannò brutalmente all'estinzione nel 1987: Il...

sistemacanonfd.blogspot.com

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

 

[Andreas Thaler]

Some articles so far I have priviously published on Photrio regarding the T90:

Thread 'Canon T90: Defective display replaced'
https://www.photrio.com/forum/threads/canon-t90-defective-display-replaced.197850/

Thread 'Canon T90: Power supply restored'
https://www.photrio.com/forum/threads/canon-t90-power-supply-restored.197807/

Thread 'Canon T90: Advanced cleaning of stuck shutter blades'
https://www.photrio.com/forum/threads/canon-t90-advanced-cleaning-of-stuck-shutter-blades.197777/


Some more should follow

+++

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

 

[Andreas Thaler]

I would like to show some details from a disassembled T90 in the following.

The components of the LCD on the top of the camera.

I stuck the red dot on it for “defective” as the IC was used for a soldering exercise.

Position of the incandescent lamp that is responsible for the LCD lighting. No LED is installed here.

Mount with lamp removed.

The lamp

Lighted up gradually from 1 V to 1.8 V (without series resistor) on the power supply.

 

[Andreas Thaler]

View of the mirror box from above.

BLUE: the LCD bar display for spot measurement.

YELLOW: the 7-segment LEDs for displaying numbers and letters in the viewfinder.

 

[Andreas Thaler]

Details of the solid mechanics of the mirror box.

A high-performance unit.

Here I'm currently trying to activate the mirror magnet with a magnetic throttle, but that didn't work.

 

[Andreas Thaler]

Every T90 owner's nightmare.

These indicators mean either stuck shutter blades (repairable) or inactive shutter magnets. There is currently no known countermeasure for this.

The locking magnets are located under flexible circuit boards. To get there you have to desolder and dismantle. The second nightmare.

 

[Andreas Thaler]

A known problem with the T90 concerns the adjustment wheel behind the trigger button, which sometimes skips click positions.

For example, with aperture priority in aperture priority mode.

It should be possible to change from 2.8 to 4 with one click, but sometimes it takes another or more spins.

That's unconfortable.

So I took a closer look at the wheel.

The assembly with wheel, trigger and spot measurement button is screwed to the handle.

After removing the glued-on leather covering, three screws can be reached.

The assembly can then be removed ...

... however, this will loosen the soldered delicate wiring in the handle.

The camera is now inoperable.

Re-soldering is possible (you would have to check the service manual to see which cable needs to be soldered where), but the cables are so tight that they would have to be lengthened in order to be able to reassemble the unit.

I refrained from doing that and decided to repurpose this T90 as a spare parts depot. Also because of the EEE error which I cannot fix.

Now that the assembly is gone, it can at least be studied.

The assembly

Top front: trigger button
Behind: adjustment wheel
Right: spot metering button

View from below

The arrow points to the contact plate that rotates with the wheel.

Above this are the wipers that switch with the contacts.

Contact errors can occur here due to contamination or corrosion.

Rear view


The contact plate is not sealed to the outside.

This allows dust and dirt to accumulate. Moisture can also penetrate and lead to corrosion.

This example of an otherwise dirty T90, which is clean on the inside, shows that the protection anyway is still good. Nethertheless the wheel was concerned by the skiping issue.

Electronics cleaner would help here.

I tried spraying it along the shutter release button and the spot metering button when the camera was not disassembled, but none of it reached the contact plate.

The only thing left to do is to get the contacts clean again by turning the wheel several times.

This worked successfully on another T90.

 

[Andreas Thaler]

Before the T90 went into the spare parts box, I removed its immaculate focusing screen D with grid.

It's not something you see often, or if it does, it's quite expensive

The screen can be pulled out of the mirror box by lifting a spring tab.

There was once a special tool for changing which came in the box with each new focusing screen.

—
See also

T90 Focusing Screens

 

[Andreas Thaler]

I discovered this tiny ball bearing in my T90 spare parts.

I don't know where it was installed.

It's unbelievable what has been achieved mechanically here

 

[Helge]

View attachment 353830

I discovered this tiny ball bearing in my T90 spare parts.

I don't know where it was installed.

It's unbelievable what has been achieved mechanically here

Regardless of what I wrote about the actual camera, that is very, very interesting.
Since you have seen the inside of more cameras than any of us probably have or will, what is your opinion of the general build quality of the T90 and/or Canon cameras of the era, as such?

 

[Andreas Thaler]

Regardless of what I wrote about the actual camera, that is very, very interesting.
Since you have seen the inside of more cameras than any of us probably have or will, what is your opinion of the general build quality of the T90 and/or Canon cameras of the era, as such?

I think the T90 is a solidly built camera.

The mechanics and chassis are solidly made, the plastic housing is durable, even if the front panel is thin and the battery compartment looks a bit cheap. But as a unit, the T90 rightly deserves the nickname “the Tank,” I would say.

I only know the T70 from my school days.

The angular design is 80s-like, the overall impression is solid. This also applies to the Minolta 7000 of the same era, which is often underestimated.

Plastics bring many advantages in camera construction.

They can be shaped as desired, can absorb shocks and impacts, are corrosion-free and your hand won't freeze on them in winter .

I therefore think plastics deserve more respect, and today they are standard anyway.

 

[Helge]

I think the T90 is a solidly built camera.

The mechanics and chassis are solidly made, the plastic housing is durable, even if the front panel is thin and the battery compartment looks a bit cheap. But as a unit, the T90 rightly deserves the nickname “the Tank,” I would say.

I only know the T70 from my school days.

The angular design is 80s-like, the overall impression is solid. This also applies to the Minolta 7000 of the same era, which is often underestimated.

Plastics bring many advantages in camera construction.

They can be shaped as desired, can absorb shocks and impacts, are corrosion-free and your hand won't freeze on them in winter .

I therefore think plastics deserve more respect, and today they are standard anyway.

The Minolta 7000 is woefully underestimated. The main problems is LCD bleed and crumpling of the plastic rubber. But somewhat surprisingly many cameras have survived unscathed. Might be different batches of components?
The rest of he camera usually works perfectly.
A good clean example focuses very fast with a fast lens, even in quite low light, takes AFAIK all Minolta α lenses to the mid nineties and has a standard hotshoe. I find it much better than many of the ensuing cameras like the 9000, 7000i etc. Only the 7 and 9 are really better cameras.
And as you said, it's a wonderful example of mid 80s design.

 

[Andreas Thaler]

I'm already off topic, but in this context a comment about the Nikon F4, also from the 80s:

This is probably the most valuable SLR from this era, with at least the housing cladding made of plastic/rubber.

Unfortunately, it has two weak points today: obvious gumming in the mirror mechanism, which is difficult to access, and the LCD bleeding. Much worse than the Minolta 9000.

Nevertheless, these cameras often hold up better than their users of the same age

OT OVER

 

[Andreas Thaler]

A known problem with the T90 concerns the adjustment wheel behind the trigger button, which sometimes skips click positions.

For example, with aperture priority in aperture priority mode.

It should be possible to change from 2.8 to 4 with one click, but sometimes it takes another or more spins.

That's unconfortable.

So I took a closer look at the wheel.


View attachment 353822

The assembly with wheel, trigger and spot measurement button is screwed to the handle.

After removing the glued-on leather covering, three screws can be reached.


View attachment 353823

The assembly can then be removed ...


View attachment 353824

... however, this will loosen the soldered delicate wiring in the handle.

The camera is now inoperable.

Re-soldering is possible (you would have to check the service manual to see which cable needs to be soldered where), but the cables are so tight that they would have to be lengthened in order to be able to reassemble the unit.

I refrained from doing that and decided to repurpose this T90 as a spare parts depot. Also because of the EEE error which I cannot fix.

Now that the assembly is gone, it can at least be studied.


View attachment 353826

The assembly

Top front: trigger button
Behind: adjustment wheel
Right: spot metering button


View attachment 353827

View from below

The arrow points to the contact plate that rotates with the wheel.

Above this are the wipers that switch with the contacts.

Contact errors can occur here due to contamination or corrosion.


View attachment 353828

Rear view


The contact plate is not sealed to the outside.

This allows dust and dirt to accumulate. Moisture can also penetrate and lead to corrosion.

This example of an otherwise dirty T90, which is clean on the inside, shows that the protection anyway is still good. Nethertheless the wheel was concerned by the skiping issue.

Electronics cleaner would help here.

I tried spraying it along the shutter release button and the spot metering button when the camera was not disassembled, but none of it reached the contact plate.

The only thing left to do is to get the contacts clean again by turning the wheel several times.

This worked successfully on another T90.

I have just found a note from Thomas Tomosy (Camera Maintenance & Repair, Book 1) on how to lift the trigger switch assembly without damaging the cable connections. Then the contacts on the adjustment wheel can be cleaned.

To do this, the battery compartment must be removed and the cable harness installed in the handle must be loosened.

If anyone is interested, I would be happy to show it on one of my abandoned T90s.

 

[Andreas Thaler]

Today I looked at the last unresolved problem with the T90, where EEE appears on the display and HELP appears in the viewfinder.

In the SPT Journal March/April 1990

Learn Camera Repair

learncamerarepair.com

there is an extensive article about the T90, written by Larry Lyells, probably the leading expert in the field of camera technology of this era

I went through the troubleshooting instructions, but couldn't find this particular error on my T90 described there.

Because before EEE and HELP appear, the first shutter curtain opens, but the second only opens halfway. This would mean that the locking magnets are working. Until now I assumed that with this error the two locking magnets did not separate.

It could be that the second shutter curtain is damaged, see arrow. The dent would be an explanation for the curtain not closing. But I'm not sure if it's a rivet on the slat like underneath. I'll check this on a working T90.

I took some measurements with the oscilloscope. The measured pulses and DC values were correct, so also the DC/DC converter, which brings the 6 volt battery voltage to 18 volts, should work. Maybe an SMD diode is not working properly, but the instructions for measuring were not clear to me.

I then stopped the measurements because I didn't think I was on the right track. Maybe it's a mechanical problem? I do‘nt know.

In any case, I was able to get to know some of the details of the T90 again


Conclusion

• EEE and HELP obviously don't always have to do with blocked magnets, it could also be a problem in the circuit.
• I don't think the instructions you often read about checking solder joints are very helpful. I haven't seen a bad solder joint in the T90 yet.
• The SPT Journal contains troubleshooting instructions, which essentially consist of voltage measurements on the components in order to determine whether the component is defective.
• Even if that is the case, the question remains whether an exchange on the tightly installed circuit board will be successful.
• I'll stay on the topic, maybe new approaches to solving the problem will emerge.

The ground terminal of the oscilloscope is connected to the chassis of the T90, which is made of metal.

A pulse that can be measured when the two shutter curtains are triggered corresponds to the setpoint for each shutter curtain.

Voltage measurement on the DC/DC converter, which is accessible after removing the battery compartment on the bottom of the camera.

An SMD diode in this area could possibly be defective.

 

[Andreas Thaler]

It could be that the second shutter curtain is damaged, see arrow. The dent would be an explanation for the curtain not closing. But I'm not sure if it's a rivet on the slat like underneath. I'll check this on a working T90.

The second shutter curtain is ok at this point, I compared it to a second T90 which works:

It's a shame, that would have been a simple explanation for the problem

 

[koraks]

An SMD diode in this area could possibly be defective.

I see a SOT23 part and a SOD part just above it (the little glass one). The SOT23 may be a diode; if it is, it's likely a double diode. Might be something like a TVS diode with basically two fast diodes in series. The other one might be a zener diode, but also a regular or Schottky one. Putting a meter on both of them in various ways should give some insights.

It's also possible the SOT23 is in fact a transistor; the combination of a 3-pole part and a diode in series with it reminds me of a low-side coil driver with a bucking diode on top of it. If this is the case, you should be able to measure a low resistance of the coil in parallel with the diode. If the SOT23 part is indeed a transistor, it's much more likely to have failed than if it's a diode. The latter are pretty robust, the former much less so.

 

[Andreas Thaler]

I see a SOT23 part and a SOD part just above it (the little glass one). The SOT23 may be a diode; if it is, it's likely a double diode. Might be something like a TVS diode with basically two fast diodes in series. The other one might be a zener diode, but also a regular or Schottky one. Putting a meter on both of them in various ways should give some insights.

It's also possible the SOT23 is in fact a transistor; the combination of a 3-pole part and a diode in series with it reminds me of a low-side coil driver with a bucking diode on top of it. If this is the case, you should be able to measure a low resistance of the coil in parallel with the diode. If the SOT23 part is indeed a transistor, it's much more likely to have failed than if it's a diode. The latter are pretty robust, the former much less so.

Ask the expert

Here is the corresponding layout from the SPT journal:

I'll have to focus on the matter further. The troubleshooting instructions were too extensive for me.

It's like flying blind because you don't have an overall understanding of the circuit. Therefore it is difficult to draw conclusions. And I can't solder the circuit there in sober condition

 

[koraks]

Ah, double diode. If you place a meter across the terminals of D3 you should measure something in the range of 300-800mV as the forward drop on those diodes. If you don't, something's not right.
D4 looks like it's associated with the DC/DC converter, but sadly, the schematic mostly captures spatial arrangements and not electrical circuitry. I would *guess* it has the cathode pointing towards the positive (+18V) output of the DC/DC and the anode to virtual ground and thus protect the circuitry from negative spikes. That's just a wild guess though. It may just as well be a series pass diode to protect downward circuitry from reverse polarity.

Anyway, start by measuring both D3 and D4 to see if anything's amiss there.

 

[Andreas Thaler]

Thanks, will do.

Here‘s the block diagram and partial schematic:

Are these copies a copyright violation? If so, please delete it.

 

[Andreas Thaler]

But now I'm wondering whether the problem with the second shutter curtain can actually be an electronic one.

If I understood correctly, the focal plane shutter in the T90 is also mechanical. This means that it is tensioned via a motor and triggered electronically via two magnets. What then follows is a mechanical process until the shutter is cocked again.

So if the second shutter curtain stops halfway, that means there is a malfunction in the mechanical process. If its magnet had not triggered, the shutter curtain would not have moved at all?

 

[Andreas Thaler]

Or the second shutter curtain is released too late by its magnet and therefore cannot move completely. That would then again be an electronic problem.