Canon digital rebel 300D mirror problem

I am hoping someone can help with my problem with my 300D. When I shoot my first shot, the camera functions properly in all modes. On the second shot, it will try to raise the mirror but the mirror does not go up. It only moves a very small amount. Subsequent attempts may produce a normal exposure sequence or the partial mirror raise type. Eventually it may go to an err99.

When I go to sensor clean mode, the mirror will either raise normally or seem to get stuck. If it is stuck, I can give it a very gentle nudge and it will pop right up. When the mirror lifts, the shutter is always open. Once I get the mirror to lift in sensor clean mode, all subsequent attempts work properly.

I then installed the undutchables firmware and implemented mirror lockup with a 4.5 second duration. Then I went to Tv mode and set the shutter speed to 3 seconds so that I could watch everything that happens. Sometimes the mirror will stick but it always goes up with a gentle nudge. The shutter always works properly.

I then restored the firmware to the latest Canon version.

This doesn't seem to be the sub mirror pin problem because the sub mirror seems to work every time. It doesn't seem to be a bad shutter either. The little spring on the right side of the mirror ( as you are looking at the mirror) looks like it is in the right position.

I also tried removing the main and backup batteries and the CF card for 30 minutes to reset the system. This had no effect.

I tried two other lenses which work well on my other 300D to no available. I tried a different CF card. A fully charged battery. So far, nothing has had any affect.

Has anyone ever seen this problem? Do you know how to fix it?

Thank you.
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  1. Update.

    Nothing has really changed. One thing that I find curious is that the "stuck mirror" problem only occurs when the camera is in an exposure mode as compared to a sensor clean mode. So I am wondering what could be different? Could it be that the sequence of events is different in sensor clean? Just some more observations.

    I am thinking about the possibility of introducing some contact cleaner liquid such as CRC into the opening on the left where some mechanical parts live but I am a little scared to do it. The current value of a used, broken 300D does mitigate my fear some. Does anyone have any thoughts about the CRC idea?
  2. My first thought would that it would probably be more expensive to replace than to buy a new 300D body. Err99 usually results in motherboard replacement, if you have a mirror problem then they may have to replace the whole assembly.

    It's clearly not functional currently, if you are going to introduce cleaner then be careful due to electronic exposure.
  3. Update.

    Today, I sprayed some CRC QD electronic parts cleaner into the camera. I lifted the primary mirror and sprayed the CRC into the opening near the left hinge using the supplied nozzle tube. I then let it dry for a while and turned it on. To my amazement, it has worked perfectly ever since. I have now fired 150 shots without one single malfunction. I am really sold on the CRC stuff. I think it must have just been a little sticky or maybe there was a little dirt on the mechanicals that was irrigated and removed to a safer area by the CRC liquid. The CRC is a fast drying liquid that does not leave a residue and is safe for electronic and plastic parts.
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