Remove the back and lens.
Advance the camera and trip the shutter release holding the release down. Look through the back of the camera and make sure the two baffles are fully open, especially make sure the top baffle is up. Let go the shutter release and make sure the baffles snap back fully closed.
Put the lens on the camera. Set the shutter speed to 1 sec. and the f/stop to smallest (f/22). Point the camera out the window or toward a bright light and watch through the back as you trip the shutter multiple times. Make sure that when you see the shutter open the f/stop is fully closed and you detect NO movement in the f/stop blades.
Fire the lens on all shutter speeds. Look through the back and make sure you see the flash of light from each shutter activation.
Fire the lens on all shutter speeds and listen to the gear escapement on the slow speeds -- you're listening for a smooth buzz. Hesitation means cleaning is due.
If you want test the back you've got to commit a roll of film. Buy the cheapest roll of 120 film. Take off the lens. Load the film, put the back on and get a ball point pen. Trip the release and hold it down to prevent the baffles from closing. Reach in the camera with the pen and draw a line on the open frame top and bottom. Advance the camera and do it again through the entire roll. Now remove the roll and lay the film out on a table and look for even spacing in the pen lines. Overlapping spacing means time for back cleaning.
Good Luck,
Joe