mamiya M645 cds prizm finder problem

I hope someone has seen this before. I just got a cds finder with a problem. The meter is way off, and the needle is centered when off and or the battery is removed. The instrictions say the needle should be at the bottom when off, which explains why it is reading wrong. After dissassembly and inspection, the meter shows no tampering. The centering adjustment is already at the limit of travel and before removing the penta prizm so I can get to the top adjuster, if there is one, I thought I better ask. Anyone seen this before? Thanks.