Mamiya 7 65mm Lens: Shutter Magnet Not Holding
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
The Mamiya 6/7 lenses are fairly robust but lately I have been seeing a lot of them for service. Maybe age is catching up with them.
This 65mm lens came into the shop with a symptom of the shutter not releasing. What was actually happening was that the shutter was not staying cocked and the mechanism would just release as soon as the winding stroke was done. After some disassembly and close inspection, I found that the shutter magnet was not holding the armature in place.
The magnets in cameras are mostly combination magnets- a mix of a permanent magnet and an electromagnet. The permanent magnet holds the armature in place until a jolt of current caused by, in this case, the shutter release button being pressed, discharges through the electromagnet and disrupts the permanent magnets field and releases the armature.
Photo three shows the magnet (with the protective cover removed) in the closed state. Photo four shows the magnet open. If you look carefully at the contact surface of the armature, you can see a very slight discoloration and it is this residue that was making the magnet not hold in the closed position. The video shows what was happening when the shutter was cocked - the magnet should have stayed closed but was opening immediately due to the contamination on the armature. Cleaning of the magnet and reassembly of the shutter and all is well.
