RB67 90mm f/3.8 Early Version: Delayed Shutter Opening
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
Servicing a Mamiya 90mm f/3.8 lens for RB67. This is an early version (July 1973) with the sync terminal permanently attached to the housing as seen in photo three. Later versions had a removable sync terminal that could be replaced when worn or damaged. This particular example came into the shop with a very typical issue: When fired, there was a delay in the shutter opening. This is caused by dried lubrication on the main cocking/release ring inside the shutter. Solution is disassembly of the shutter, removing the relevant parts, cleaning and lubrication.
In the case of this shutter, the flash sync circuit showed a very high resistance on testing as seen in photo four. After cleaning and burnishing the sync contacts shown in photo five (copper colored springy parts in the center of the photo), the flash sync circuit returned to a resistance within factory specs seen in photo six.
