Mamiya 7II Battery Cover: Metal vs Plastic Top Versions
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
This post is about a bit of minutiae regarding the Mamiya 7II that I have not seen addressed before.
From the beginning of production in April 1999 until May 2000, the battery cover was all metal. By May, it was changed to a design with a plastic top. This was because Mamiya was concerned about battery drain from the metal top to the metal strap lug.
The battery had a negative ground through the system so the body casting, including the strap lugs (which were of unpainted metal), had a negative potential. The bare metal battery cap had a positive potential and if you held the camera just the right way, your hand could provide a path between the battery cap and the strap lug and probably enough of a low resistance to cause current to flow and battery drain. I am not so sure this was a big issue in practical terms but Mamiya considered it enough of a potential problem to redesign the battery cap with a plastic top.
Photo two shows the early metal cap and photo three shows the plastic cap (after May 2000). Photo four shows the interior of the caps, all metal on the left. The last photo shows the old (pre May 2000) body with the metal cap and the strap lug close by.
This was probably not considered an issue with the original Mamiya 7 as although it had a metal battery cap, it was painted black and the strap lugs were painted metal and there was not a strap lug on the side of the camera that had the battery cap.
