Mamiya 7II: B Setting Failure and Battery Drain
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
This Mamiya 7II arrived with two issues: 1.) B shutter setting did not work and 2.) Battery drain. Turns out they were related problems.
The camera, owned by a school, had a sticker on the top warning to “Turn me off”. What was happening is that the light meter was staying energized, drawing around 8mA of current and this would kill the battery after a short time. My first thought was that the cable release socket was damaged but that was not the issue. On disassembly of the camera, I found some wiring that was not in good shape. In fact, one of the wires looks like it had been cut (photo four)! After fixing things up, the camera is working well and B shutter speed has been restored.
Photo five shows the setup that I use to measure battery drain on the Mamiya 7 models: a battery eliminator screwed into the battery compartment with power being supplied by a bench power supply (upper left in photo) and current passing through a multimeter measuring mA (center right in photo). If you do any sort of camera repair, I would recommend a setup to measure current as that can tell a lot about the workings of the circuit.
The video shows the test setup being used to measure current: when the shutter release button is pressed, the light meter will energize and pull around 8 mA of current. After a few seconds, the light meter will turn off and you should read close to zero micro amps. Some cameras have specs that allow a few micro amps to flow even when turned off.
