Like other early EOS cameras, the EOS 600/630 often suffers from the "sticky shutter" issue, which manifests itself as a tar like substance fouling the shutter blades. This is caused by decomposition of a small rubber block in the bottom of the shutter unit. There are ways in which this problem can be managed, however. It's possible to remove the tar using cotton buds lightly moistened with cellulose thinner (xylene) provided you take care not to put too much pressure on the shutter blades. Don't use so much thinner that you end up spreading the tar into other parts of the camera, use the absolute minimum needed to dissolve and remove it. If this is done carefully and repeatedly, all trace of the tar will eventually be removed and proper function ensured, you may have to do it four or more times to remove all the gunge but it will do the trick eventually. Store the camera lying on it's back when not in use. I also suggest you keep it in an airtight container with some silica gel.
Electronic problems also sometimes occur with this camera, I had one in which would short out and ruin a battery every time the LCD illuminator button was pressed. After I took the top plate off and disabled the button using superglue, there were no more problems. Problems like this usually result from poor quality control and don't seem to occur to the same extent in the EOS 650 and 620 cameras
When in working order, the EOS 600/630 is a useful camera with it's die cast chassis, multiple exposure modes and built-in 5fps motor drive. Personally, I prefer it over the EOS 100 even though that camera has a higher specification in some respects.
If you find the prices of EF lenses a little high, a popular alternative is to use a manual focus lens with an adaptor. The short back focal distance of the EF mount makes it possible to adapt most manual focus lenses, including M42 screw mount, Nikon F, Contax/Yashica, Rollei, Olympus, Tamron adaptall and others. Minolta and Canon FD lenses can only be used with adaptors containing additional optical elements, which act as mild teleconverters and usually reduce the optical quality. Certain lenses have protruding rear elements which will foul the mirror of the EOS 600 in operation. This applies to the Enna 28mm f3.5, the Rollei 35mm f2.8, certain Leica wide angles, and the Zenitar 16mm with M42 mount.
Some lens adaptors can cause the camera to lock up, due to their activating a switch in the camera body just behind the lens mount, visible on the left hand side when viewed from the front. A minute's work on the adaptor with a multi-tool is all it takes to eliminate this problem, you just remove the part of the mounting flange which comes into contact with the switch.
I tried using a Pixco AF confirm M42 adapter on my EOS 600, but the camera just locked up. The same adapter works fine on the EOS 1000 Rebel.
When using the EOS 600/630 or the EOS 650 or 620 with a manual focus lens and adaptor, you can use stopped down metering in either the Av (aperture priority) or Manual modes. In either case, the first thing you have to do after selecting the mode is to set the aperture indicated on the LCD top panel to 1.0. In Av mode, the camera will then set the shutter speed for correct exposure as you adjust the aperture on the lens. In Manual mode, you can set the shutter speed you want, then press the button marked M to the side of the lens mount to get an exposure reading, which is displayed as CL, oo or OP. You can the adjust the set aperture on the lens until you get the correct exposure indication (oo). Or you can use a seperate lightmeter, in which case you set the desired shutter speed on the camera body and the required aperture on the lens.