Canon T90: release magnet, EEE/HELP/bc, mirror shock absorbers and cover, front flex connector acting crazy/alternative?, victory, shutter magnets

[Andreas Thaler]

Having suffered setbacks with my recent T90 projects, my pride was bruised

So I made another attempt and pulled the next T90 out of the repair box.

Today I had to succeed!

Both mirror shock absorbers are missing along with their mountings, the cover is no longer where it should be.

Battery electrolyte in the battery compartment …

… and on the tripod thread.

The ground cable has come loose from its soldering point due to the electrolyte.

Since it was also contaminated inside, I replaced it,

The T90 is alive, but it doesn't fire, and the arrow on the LCD is flashing.

Clearly, the release magnet Mg2 is dirty and needs to be cleaned.

I'm using a new method to get better access to the hybrid magnet screw.

After removing the two retaining screws on the DC/DC board, the screwdriver can be positioned at a right angle.

This allows the torque to be transmitted to the magnet’s screw more effectively than previously at an oblique angle.

Done


I clean the magnet with benzine and reinstall it.

The shutter now releases …

… but immediately afterwards my old friend appears.

The C & C Troubleshooting guide for the T90 has a solution for exactly this error scenario:

LCD displays EEE, finder Help after mirror cycles.
Shutter operates for one cycle before EEE.
Power, control dial, lightmeter, release normal.

Both shutter magnets are electrically triggered directly via the shutter connector. The position of the shutter switches (SW18, 19) is then determined with a multimeter.

The measurements confirm what is seen: The first shutter curtain has triggered, but the second has not.

Here you can see the switches after removing the shutter. SW18 is open (first shutter curtain) …

… SW19 is closed (second shutter curtain).

This blocks the camera, which it communicates with EEE/HELP.

 

[Andreas Thaler]

The plastic adjusting screws for the shutter curtains are intact.

I clean the two shutter magnets with benzine.

The sticky damper is removed from the shutter.

I replace the cover and the two mirror shock absorbers from a T90 for spare parts.

Spare T90: The cover has already been removed.

I'm still dismounting the dampers.

The spare parts.

Assembled

I check the mirror mechanism and the aperture control.

Everything's OK.

A clean battery compartment comes from the spare parts stock.

Cleaning foam, the most efficient method to clean housing parts.

A picture from hell!

But this error message is fine; it appears when the aperture slider is operated and the lens is in A(utomatic) mode.

After assembly, the T90 works. Only the LCD backlight won't turn on and the viewfinder LEDs won't turn off.

Then follows an hours-long battle with the front flex connector, which connects three circuit boards by pressure.

The connector goes crazy and makes a motor run, EEE appears, then bc, then the T90 is dead, then back on again. When I put the front panel on, it starts all over again, and so on.

Only when I tightened the two retaining screws on the connector's pressure plate to the correct ratio did the haunting stop.

Now also the LCD backlight works, and the LEDs can be turned off.

Madness - but victory!

 

[Andreas Thaler]

On the camera tester: 1/4000 second

1/60 s

Automatic exposure in program mode.


Everything is fine, the shutter is just a bit on the slow side.

 

[Andreas Thaler]

Conclusion

• You must not give up and must hunt down the dreaded EEE/HELP and bc.
• Technical instructions (see also my other T90 project reports) help with this or make the hunt possible in the first place.
• The front flex connector truly comes from hell. It doesn't tolerate any deviation when tightening it’s pressure plate. But it has to be overcome when you disassemble the T90 for service and repair.

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This concludes my coverage of the T90.

I hope I've given you the courage to take on this magnificent diva.

After a longer break, I'll be focusing on the Canon A-1, the T90's predecessor. It's just as impressive, and there's excellent technical documentation available for it.

Good luck with your T90 repair projects!


+++

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

 

[Andreas Thaler]

Access to the mirror box mechanism and the shutter with the front flex connector closed

The front flex connector proved to be a key point when removing the mirror box and shutter.

When reassembling the T90, contact problems can arise here, undoing all the previous repair work.

Therefore, I looked for a way to remove the mirror box and shutter with the front flex connector closed.

---

All pictures of a T90 for spare parts:

Front flex connector closed with pressure plate.

Beneath the pressure plate, three circuit board components are sandwiched together.

A large portion of the T90's data communication passes through this connection.

Between the gold-plated contact rows are elastic connector strips that, after decades of attachment to the contacts, have become slightly stuck.

I've always removed them when opening the connector. I think it's a good idea to only remove them on one side to minimize disruption to the entire assembly.

I was able to remove the mirror box to this position with the front flex connector closed.

The mirror box is still connected to the housing via two circuit boards.

This also makes the shutter underneath accessible which can be removed for service.

The dismantling effort is reduced.

There is also no need to desolder the cables on the front flex connector.

The AE unit on the side of the mirror box and the auto-diaphragm unit below it can be completely removed for service work.

See also

Post in thread 'Canon T90: Service and repair using practical examples'
https://www.photrio.com/forum/threa...-using-practical-examples.213586/post-2898959

Post in thread 'Canon T90: Service and repair using practical examples'
https://www.photrio.com/forum/threa...-using-practical-examples.213586/post-2898950

The retaining screws of the shutter are also accessible (the third screw at the rewind side of the shutter is directly accessible).

With patience and sensitivity, the shutter can be removed as usual.

It just catches slightly on the plastic plate beneath the front flex connector, which would otherwise be unscrewed.

Installation should also be possible this way.

Here, you have to pay attention to the flexible circuit board strip that connects the shutter to the main board.

I had rotated the shutter twice to get to a position where I could open it. In doing so, the circuit board tore and a circuit track was severed.

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Conclusion

Is this method a realistic alternative to opening the front flex connector when disassembling the T90?

Does it eliminate the risk of potential contact problems?

• If it's about working on the mirror box, cleaning the shutter magnets, or checking the condition of the adjustment screws on the two shutter curtains (the screws are made of plastic and can break. The T90's shutter can be adjusted using these screws even when the shutter is installed. You just need to know their condition.), then yes.
• If the shutter needs to be disassembled to remove the sticky damper, then I'm undecided. Since the shutter is attached to a strip of circuit board, its movement is limited. Working on it isn't impossible, but it does require some preparation to ensure it's securely fixed. In any case, damage to the circuit board must be avoided.
• The shutter should also be able to be reinserted. Despite the friction point with a cover plate.
• This method puts stress on the board connections. Anyway I couldn't find any damage except for the area around the shutter.
• Whether it works will only be shown by a brave attempt with a T90, which is to be repaired in this way

+++

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

 

[moggi1964]

Thank you.

 

[Andreas Thaler]

Thank you.

 

[Andreas Thaler]

Removing the shutter board to replace/service the magnets

The circuit board on the shutter can be easily removed to replace the magnets or for servicing, e.g., for a more thorough cleaning than is possible with the shutter installed.

Here, I've cut the shutter from the spare T90 from its connector on the main circuit board with a scissor for a quick demonstration.

This brutal approach makes photography more convenient, as I don't have to adjust the housing with the bulky mainboard to which the shutter is connected

Besides, the main board only serves for spare parts; replacing it completely would be too much work for me and, according to the manual, requires extensive adjustment work.

---

The shutter from another spare T90 with complete board connection.

Cut here.

1 screw (green, already removed here), 4 soldered joints (white)

The board can be liftet after removing the screw/desoldering. It is attached to small hooks on the front left and right.

The four copper enamel wires of the magnets are still soldered to the board.

Desoldered.

The brass plate underneath can be lifted off.

Overview

When desoldering, the insulating varnish on the wires peels off by a few millimeters.

This must be taken into account when soldering to avoid a short circuit after assembly and bringing into service.

The two magnets with their armatures in full glory ready for replacement/service.


+++

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

 

[Andreas Thaler]

[addendum shutter]

View attachment 399890

Here, you have to pay attention to the flexible circuit board strip that connects the shutter to the main board.

I had rotated the shutter twice to get to a position where I could open it. In doing so, the circuit board tore and a circuit track was severed.

To avoid stress on the shutter's circuit board, it can be desoldered - as with regular disassembly.

Then the shutter is free after removal.

The shutter connector with three (five in newer version) soldered joints is located on top of the prism.

 

[Yashica]

Wow, really complicated stuff. I'd just have replaced the T90 with another T90 then, buying it online.

 

[Andreas Thaler]

Wow, really complicated stuff. I'd just have replaced the T90 with another T90 then, buying it online.

 

[Andreas Thaler]

In my experience, almost every T90 needs some work.

Almost always, it's the shutter, which is affected by the sticky damper inside.

 

[Yashica]

Really cool, Andreas. So you're an T90 expert. Are you also being familar with other 35mm SLRs? Or just the T90?

 

[Andreas Thaler]

Really cool, Andreas. So you're an T90 expert. Are you also being familar with other 35mm SLRs? Or just the T90?

I have been able to gain some repair experience in various 35mm systems:

Photo equipment from the 1980s: Repair projects and recommendations

I would like to bring together a selection of my previous contributions here in the hope that they will help readers with their work or inspire them to get involved in repairs. It is always worth trying to repair something, because if you do nothing, a camera or lens will definitely remain...

www.photrio.com

 

[Yashica]

I have been able to gain some repair experience in various 35mm systems:

Photo equipment from the 1980s: Repair projects and recommendations

I would like to bring together a selection of my previous contributions here in the hope that they will help readers with their work or inspire them to get involved in repairs. It is always worth trying to repair something, because if you do nothing, a camera or lens will definitely remain...

www.photrio.com

Very cool, respect! I am familar with soldering PCBs, also SMDs since the later 80s, but haven't done this for years. But it's like bicycle riding, you'd never forget it. But i am not a camera expert, repair guy. I don't have the time, the patience & equipment for this, Kudos. I created only HiFi/Class-A Amplifiers, decades ago. Honestly, i've sold my T90 decades ago. It's really interesting to see, how much electronics/mechanics was put inside the T90, full under the roof. I heard often into forums about issues with the magnets on the T90. My copy was still fine, when i sold it.

And the nowadays asking price...well, you could get even a fine FF DSLR from CaNikon for it's asking price. But every camera, -gear does have it's own followers, aka Fans & Cult. The T90 was very advanced into 1986 - but also a huge chunk of plastic, like many Canon 35mm SLRs have been...i couldn't justify to keep mine, with just ~3 FD lenses, whileas owning serveral other SLR systems at the same time.

 

[Andreas Thaler]

Very cool, respect! I am familar with soldering PCBs, also SMDs since the later 80s, but haven't done this for years. But it's like bicycle riding, you'd never forget it. But i am not a camera expert, repair guy. I don't have the time, the patience & equipment for this, Kudos.

When it comes to repairs, I can put all my problematic traits to good use: stubbornness, egomania, obsession, pedantry, and inflexibility.

All of this contributes to my success rate. In the workshop, alone

Plus my joy in writing, which was also largely my job.

I created only HiFi/Class-A Amplifiers, decades ago.

Then you know about frequency technology, which is a completely different level and makes the transistor more complicated than in cameras

Honestly, i've sold my T90 decades ago. It's really interesting to see, how much electronics/mechanics was put inside the T90, full under the roof. I heard often into forums about issues with the magnets on the T90. My copy was still fine, when i sold it.

The magnets are sensitive to contamination, I can confirm that.

The shutter contains a damper for the curtains, which degrades on practically all T90s and clogs the slats. You can partially clean it from the outside with a shortcut, but you can only do it thoroughly by disassembling the shutter.

The main LCD can fail probably due to a defective IC; I recently had a broken double diode.

The famous command wheel often skips, but all of this can be fixed; there are excellent troubleshooting guides for it; see my posts on the T90.

The T90 was very advanced into 1986 - but also a huge chunk of plastic, like many Canon 35mm SLRs have been...

Appearances can be deceiving. The exterior is made of high-quality, non-degradable plastic. Inside, the relevant mechanical parts, the mirror box, and the area around the film gate are made of solid resp. die-cast metal.

All of this makes the T90 resistant to use and rough handling.

The design of the mirror box demonstrates its quality. This is mechanics for heavy-duty use:

i couldn't justify to keep mine, with just ~3 FD lenses, whileas owning serveral other SLR systems at the same time.

No comment

 

[Andreas Thaler]

The shutter should also be able to be reinserted. Despite the friction point with a cover plate.

This just worked in a test on the spare T90.

That gives the green light for an alternative removal of the mirror box and shutter for the next T90 repair project

The disassembly steps are slightly different than before, or some are being added. I'll document this in the report.

If it works in practice, the problems with the front flex connector are solved, at least for this type of repair.

 

[Andreas Thaler]

But that doesn't mean the alternative method is risk-free.

Here, I overbent the circuit board, and it cracked. While this can be repaired, it's not an easy job.

Therefore I'll proceed with extreme caution, and if it doesn't look good, I'll stop and continue by trying not to completely remove the elastic connector strips. Perhaps that will help tame the front flex connector.

With the T90, it's never boring

 

[Yashica]

When it comes to repairs, I can put all my problematic traits to good use: stubbornness, egomania, obsession, pedantry, and inflexibility.

All of this contributes to my success rate. In the workshop, alone

Plus my joy in writing, which was also largely my job.

Haha, good one Andreas! Well, at least you've found something, which makes you happy...as hobby, passion.

Then you know about frequency technology, which is a completely different level and makes the transistor more complicated than in cameras

Honestly, i was not using any scope, just a bit of Eagle layout, PCBs....i like quality sound, HiFi, but unlike the 90s, i can't afford it nowadays...just listening with a good headphone amp via my HD 650 my FLAC files via PC, most of the time...it's good enough for my taste.

The magnets are sensitive to contamination, I can confirm that.

The shutter contains a damper for the curtains, which degrades on practically all T90s and clogs the slats. You can partially clean it from the outside with a shortcut, but you can only do it thoroughly by disassembling the shutter.

The main LCD can fail probably due to a defective IC; I recently had a broken double diode.

Interesting find, especially the flexible circut board, into contrast to the relative "dull" thick soldering points.

The famous command wheel often skips, but all of this can be fixed; there are excellent troubleshooting guides for it; see my posts on the T90.



Appearances can be deceiving. The exterior is made of high-quality, non-degradable plastic. Inside, the relevant mechanical parts, the mirror box, and the area around the film gate are made of solid resp. die-cast metal.

All of this makes the T90 resistant to use and rough handling.

The design of the mirror box demonstrates its quality. This is mechanics for heavy-duty use:

View attachment 399979



No comment

Yes, the mirror box does really look rugged, compared to other 35mm SLRs...i do have ordinary, not huge hands (size 8.5) so i prefer a smaller body, say the XD series for instance fits me well. Suprised to see all that metal gears, looks like solid engineering from Canon, back into 86. It looks, it could withstand some heavy use.