1986 model camera, parts will be hard to find and repairs expensive. If you intend to keep shooting film you still have one working.
Are you interested in digital? An equivalent digital model from the EF line would probably be less money. Especially since the EFs are moving over for the RFs.

There are thousands of good EF bodies and lenses available used in VG to EX condition. Maybe even from someone here on the Hog. I for one am considering selling 1 or 2 of my EFs, probably my 80D or 90D, both are crop sensor but excellent sensors in them. In addition I have an even older 6D full frame, simple but takes excellent images. It is still rated among the good low light cameras - trying to do a full moon shot of a tree line with the trees all black it actually tried to do the scene in full color, dim and muddy colors, but they were there. I also have a 5Div full frame (=35mm size sensor) and 7DII crop sensor bird/wildlife/action camera.

Hmm, I am almost deciding to offer you one of those if you want it. I would have to look up the values of the bodies and some of the lenses I have. I started using RF bodies with the kit lens and an adaptor for all my EF lenses but then I bought RF lenses in my favorite sizes so I have 5 or 6 EF lenses in additon to the kit lenses for each body that I would consider parting with.

A simple google: google canon t90 eee error

takes you to numerous website discussions and multiple 'how to' videos to attempt a repair.

As noted already, theses cameras are likely easier (cheaper) to replace than to repair. Other ideas include changing to another FD-capable film body, although few have as much automated capabilities as the T90. But, for manual focus, the F-1 models are built like tanks and never seem to fail.

Personally, I gave up on manual focus film shooting, selling my MF bodies and keeping the FD lenses for use on a digital mirrorless Sony body, via an FD adapter. These MF lenses are way more fun to shoot on digital mirrorless. With the enabling mirrorless technologies, the lenses are much easier to use, delivering superior results to anything I ever achieved in film via MF.

Thank you for your tips. I do have other film cameras including 2 F1s purchased new many years ago. Because I purchased and use the T90 for many years, it has a special place in my heart. As it turnsout, it is very easy to fix. This camera is made to be used and not stored in a drawer (the last time I use it was about 6 or 7 years ago) right by the shutter preview button, under the skin, there is a magnet that it becomes demagnetize with time, I found the video on how to repair the camera in YouTube and since I don't have jewelers screwdriver, I thought for a wile and decided to use powerful magnets from ourside the skin to remagnetize the "thing" inside the camera that suppost to be magnetized. It worked! Now I just have to shoot a few photos every day and don't store it again.

Thanks friend

Ignacio

I looked up "Canon T90 EEE error" on youtube and several things came up. I only looked at one about removing the front plate,. I won't go into it here because it would be too convoluted. The video I looked at was just a little over 8 minutes long was very complete and helpful. One thing I can share is that the guy says The T 90 needs to used on a fairly regular basis, or at least fired off, to keep it magnetized. "The tank" remains my favorite film camera. I need to get mine going again and run some film through it. Good luck with yours.