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Cooltouch
Tinkerer
Username: Cooltouch
Post Number: 220
Registered: 01-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, September 27, 2012 - 09:08 pm: | 
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I just did a search of the archive, and found at least one answer to questions I have about a Canon T90 I just acquired. The camera is in nice cosmetic condition, including the LCD, and it is not exhibiting the dreaded "EEE" error message, but it is exhibiting a blinking transport triangle on the main LCD, which according to a response I found in my search, indicates the mirror magnet is the culprit. However, it occurs to me that, since the mirror has to trip before the shutter does, I very well could be looking at an "EEE" error as well when/if I can resolve the mirror issue.
My questions are as follows:
How do I remove the T90's mirror box? Or to be more precise, how do I get to the T90's mirror box so I can remove it? I've removed A-series Canon mirror boxes, but this is way different. I see one phillips screw above the lens mount and two below it that appear to be the only screws holding the front facia in place. Are there more hidden ones somewhere?
Next, let's assume that I've removed the mirror box now. Okay, now what? How does one deal with a mirror magnet to get it to behave properly? Am I supposed to demagnetize half of this arrangement somehow? Suggestions on how to do this?
Next, if I can assume the worst and let's say that I've successfully delt with the mirror magnet issue, only to see the "EEE" error code crop up, again, any suggestions on how to get where I need to get to demagnetize the shutter magnets would be most welcome.
Heh, I'm not asking for much, am I? Geez, I hope not. This really is a clean T90 and, while I have the option of returning it, I'd really like to make it mine. |
Cooltouch
Tinkerer
Username: Cooltouch
Post Number: 226
Registered: 01-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, September 29, 2012 - 05:19 am: |
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Okay, I've made a small amount of progress with this camera. First of all, I figured out how to remove the front fascia. You remove the three screws in the front that I mentioned in the above message, then there are two more on the side where the back release switch is located that hold the switch and a panel onto the camera. After removing those two screws, the panel separates into its subcomponents, so be ready for that, and then the fascia just falls forward. Unlike some earlier electronic cameras I've worked on, like the A-1 and AE-1Program, the electronic components are laid out in a very logical and almost simple manner. Still, it doesn't mean I know where to start with the electronics, though. But at least I can get to the mirror box without too much difficulty, I'm hoping.
I've been doing some searching and reading up on the stuck shutter issue. Most of the information I've been finding has to do with the shutter and freeing it up and not the mirror box. A couple of people have recommended just banging the bottom plate on a hard surface to unstick the magnets. Others have suggested that there can be a build-up of residue that needs to be cleaned off. One guy wrote:
"The sticky shutter problem relates to a rubber washer which is involved in the operation of the shutter. With age and atmospheric conditions, it tends to perish and become sticky, so that it impedes the operation of the shutter. Frequent use can delay the stickiness from 'glueing up' the shutter, but once started, the only long-term remedy is to have the shutter repaired, when the rubber washer is replaced, and so another 10 years or more can be enjoyed with the camera working correctly. A good short term solution is to lightly clean the shutter diaphragm with a cotton ball and lighter fluid."
All of these responses indicate to me that the issue is not one of the magnet transferring its magnetic properties to the piece it comes into contact with. Although, one fellow did recommend to set the shutter to B, then to trip the shutter and then remove the battery pack. So the magnets don't contact each other, he said. I have my doubts that his solution will actually work.
Another guy wrote of a method that he used that involved holding down the shutter button and pressing in and releasing the stop-down lever repeatedly.
For me though, the first hurtle will be the mirror box magnet. Does anybody here know if the flex circuits and pentaprism need to be removed before the mirror box can be lifted free? |
Brcamera
Tinkerer
Username: Brcamera
Post Number: 211
Registered: 08-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, September 29, 2012 - 10:20 am: |
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The mirror box is removed with the main flex attached. This means quite a bit of desoldering between the main flex and the rest of the camera. Before going that far, I would check the release magnet in place. If you desolder the release magnet wires (black and orange) from the top of the flex, you can apply 3 volts to them and the mirror should release if the magnet is good. |
Cooltouch
Tinkerer
Username: Cooltouch
Post Number: 227
Registered: 01-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, September 29, 2012 - 11:55 am: |
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Does it matter which orientation I apply the 3 volts? I.e., + to orange, - to black, or vise versa?
BTW, the mirror is not stuck in the up position. Will applying 3 volts cause it to actuate, or just lower itself if stuck in the up position? |
Brcamera
Tinkerer
Username: Brcamera
Post Number: 212
Registered: 08-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, September 29, 2012 - 02:32 pm: |
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Orange is positive, black is neg. If the mirror box is charged (cocked) then the mirror will release. |
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