I am on vacation with a PX-28 of unknown vintage in a Mamiya 645 1000S. When I checked the camera last night the shutter fired and the PD-S finder worked. Now the shutter will still fire but the PD-S finder will not show any lit diodes. I have set the shutter speed to the same number on both dials. It's sunny so metering is not a big problem but I have a separate meter with me anyway. Should I be concerned that the PD-S finder doesn't seem to be working or is this just a sign the battery is barely alive? If the shutter stops firing or if I can't find a new PX-28 locally then I have a Canon FTbN with four lenses to fall back on.