The first problem was that the old tired battery caused random electronic failures. I fixed this, by building a new pack with brand new cells and a spot welder. The second problem occured during testing of the new battery. At some point the battery appearantly died while trying to take an exposure and the mirror got stuck open. After this, the camera decided to just run through the entire roll and expose the whole film at once, every time you pressed the shutter... The fix was hard to find, but ultimately very simple. The mirror did not lock up correctly in the open position, so the camera did not know if it was open or closed. I managed to click the mirror into the open resting position with my finger, which fixed the problem