Canon T90: Shutter removal procedure

Andreas Thaler

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One problem for which I at least do not know of a solution is inactive shutter magnets in the Canon T90, which has two of them.

The problem manifests itself in the camera releasing the mirror but the shutter remains closed. "EEE" is displayed on the camera display and "HELP" in the viewfinder. After removing and reinserting the battery holder, the same sequence can be started.

There are two possible causes for this:
  1. defective magnets (three-part) or
  2. dirt on the contact surfaces of the magnets.
In any case, the shutter has to be removed to fix it. And I consider that to be a suicide mission with the T90, with its incredibly tight internal construction.

Here are the directions in SPT Journal March/April 1990, written by the brilliant and intrepid Larry Lyells to whom we owe so many great service instructions:









I did something similar with the Nikon F4 to remove the mirror box, but in addition to the article in the SPT Journal with illustrated step-by-step instructions. That was a day job and much less complicated.

I think it's hopeless to try to tackle this.

Does anyone have a more optimistic view?


SPT Journal: March-April 1990

Society of Photo-Technologists Journal
learncamerarepair.com
 
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loccdor

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Yes I have a more optimistic view as I had this problem with my T90 after a decade of storage.

One solution that has circulated online is letting the camera's shutter stay open in bulb mode overnight. This is what worked for me.

It didn't work immediately, I found I needed to fire the shutter a few hundred times after on many speeds. But now the camera is working again.

I don't recall the reason this works, I faintly remember it having something to do with re-magnization achieved by separating the parts for a time.
 

loccdor

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My apologies for not providing a more useful comment: it seems this problem happens both in mild and extreme degrees.
 
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Andreas Thaler

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I would like to try to remove the shutter for a closer inspection and then reinstall it, but I can already see the madness ahead of me. It's a jungle of circuit boards, and you don't need a soldering iron, just a machete!
 
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Andreas Thaler

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And if it does work - here the shutter of a T90 from a section - the shutter itself still has to be disassembled …



The arrows point to the two magnets.
 

moggi1964

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I magnetised a screwdriver and slid it in to where the magnets are. That worked, I only had to remove the front left panel and I haven't had the issue since; 9 months.
 
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Andreas Thaler

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moggi1964 said:
I magnetised a screwdriver and slid it in to where the magnets are. That worked, I only had to remove the front left panel and I haven't had the issue since; 9 months.
Click to expand...

I'm sure you mean the mirror magnet? But I'm referring to the two shutter magnets, which are not directly accessible.
 

Laurent

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Andreas Thaler said:
There is probably a transition in the shutter from temporary failure to total failure.
Click to expand...

My EOS-3 developped similar symptoms to a T90, and I confirm it first was temporary (sticky shutter that did not trigger properly above 1/2000) and became more frequent if I did not use the camera enough, or less frequent if I fired repeatedly.

A quick fix I found was to activate multi exposure, fire several times in a row.

Long term fix was to sell the camera... I loved it but it was too much and drew too much attention from the subject to the camera and its settings
 
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Andreas Thaler

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Nevertheless, it must be possible to get to the shutter. Canon's service people managed to do it and had the same work ahead of them.

Perhaps they even replaced parts of the electronics and didn't bother with the procedure described by Larry Lyells?
 

Laurent

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Andreas Thaler said:
Nevertheless, it must be possible to get to the shutter. Canon's service people managed to do it and had the same work ahead of them.

Perhaps they even replaced parts of the electronics and didn't bother with the procedure described by Larry Lyells?
Click to expand...

on my longer terms plans is dismantling one of the T90s I have (5 to date, 2 with heavily damaged exterior shell) to get to this place and see if it's realistic.

Main issue for me is working in the long term with my ADHD brain constantly suggesting so many other projects...

An interesting observation about the magnets is that the T90 that had a mirror issue got it solved by removing the magnet and putting it back. Not sure the fact that I swapped the magnets between two cameras makes a difference since at the end both cameras "work" (the mirror is now working fine).
 
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