Solenoids, or simply „magnets“, can be found in every electromechanical SLR.
They ensure that the curtains are triggered at a set interval, a mirror is released or that the aperture is closed to the intended value.
As electromechanical switches, they are a link between electronics and mechanics. Without them, an electromechanical camera cannot function. Therefore, any malfunction in the magnets leads to a serious problem or even failure of the camera.
The technology behind it is as fascinating as it is effective
In its simplest form, a magnet holds an armature made of steel with its force.
A coil made of copper wire that surrounds the magnet cancels out the force of the magnet when current flows through it. This releases the armature. The switch that was previously closed is now open.
The solenoid in a Canon T90 that controls the movement of the mirror. A magnet wrapped in enameled copper wire holds a metal armature (not visible here).
If no current flows through the coil, the armature is attracted again and the switch is closed.
The aperture control solenoid on the mirror box of a Minolta 7000 AF. The armature is held by the magnet, so the switch is closed ...
… after current has flowed through the coil (here coverd with black tape) the magnet releases the armature and the switch is opened.
This is made possible by the fact that the current that flows through the coil creates a magnetic field that cancels out the field of the magnet.
This means that shutters can be opened, mirrors rised and apertures closed to the intended value using current flows that are precisely timed by the SLR's electronics.
Together with mechanical and electronic systems, this results in precise control of the SLR.
If solenoids no longer work properly or no longer work at all
it is often because the contact surfaces between the magnet and the armature are contaminated, eg. by oil.
To access the mirror solenoid on the Canon T90, the camera must be disassembled to a small extent.
The magnet and armature can then be separated …
… and their contact surfaces cleaned from contamination.
Then the magnet either does not hold the armature firmly enough or the armature sticks to the magnet and cannot be removed. This means that shutter curtains, mirrors or electronically controlled apertures no longer work as they should.
But a decrease in the magnetic force can also cause malfunctions.
See
by @forest bagger
Post in thread 'The Minolta 7000 AF repair marathon'
https://www.photrio.com/forum/threads/the-minolta-7000-af-repair-marathon.211737/post-2870002
Interruptions or short circuits in the fine coil winding made of enamelled copper wire can also put solenoids out of action.
However, in order to reach the two shutter magnets on the Canon T90, the camera has to be disassembled deeply. An effort that is not always worth it.
Cleaning or replacing defective solenoids
is often made difficult by the fact that they are installed deep inside the camera and require complex disassembly (and reassembly).
Sometimes, however, they are easy to reach, such as with some Canon A cameras, where only the base plate has to be removed to gain access.
So even with high-tech SLRs such as the Canon T90 or Minolta 7000 AF, these are not electronic problems, but simple mechanical ones that could easily be solved if these SLRs were not built so tightly.
For us DIY repairers
this means that we need less knowledge than electronics engineers to carry out a repair, but rather skills and practice in disassembling and assembling electronic SLRs.
Tutorials can help and invite you to tackle such repairs
www.photrio.com
www.photrio.com
+++
All information provided without guarantee and use at your own risk.
They ensure that the curtains are triggered at a set interval, a mirror is released or that the aperture is closed to the intended value.
As electromechanical switches, they are a link between electronics and mechanics. Without them, an electromechanical camera cannot function. Therefore, any malfunction in the magnets leads to a serious problem or even failure of the camera.
The technology behind it is as fascinating as it is effective
In its simplest form, a magnet holds an armature made of steel with its force.
A coil made of copper wire that surrounds the magnet cancels out the force of the magnet when current flows through it. This releases the armature. The switch that was previously closed is now open.
The solenoid in a Canon T90 that controls the movement of the mirror. A magnet wrapped in enameled copper wire holds a metal armature (not visible here).
If no current flows through the coil, the armature is attracted again and the switch is closed.
The aperture control solenoid on the mirror box of a Minolta 7000 AF. The armature is held by the magnet, so the switch is closed ...
… after current has flowed through the coil (here coverd with black tape) the magnet releases the armature and the switch is opened.
This is made possible by the fact that the current that flows through the coil creates a magnetic field that cancels out the field of the magnet.
This means that shutters can be opened, mirrors rised and apertures closed to the intended value using current flows that are precisely timed by the SLR's electronics.
Together with mechanical and electronic systems, this results in precise control of the SLR.
If solenoids no longer work properly or no longer work at all
it is often because the contact surfaces between the magnet and the armature are contaminated, eg. by oil.
To access the mirror solenoid on the Canon T90, the camera must be disassembled to a small extent.
The magnet and armature can then be separated …
… and their contact surfaces cleaned from contamination.
Then the magnet either does not hold the armature firmly enough or the armature sticks to the magnet and cannot be removed. This means that shutter curtains, mirrors or electronically controlled apertures no longer work as they should.
But a decrease in the magnetic force can also cause malfunctions.
See
by @forest bagger
Post in thread 'The Minolta 7000 AF repair marathon'
https://www.photrio.com/forum/threads/the-minolta-7000-af-repair-marathon.211737/post-2870002
Interruptions or short circuits in the fine coil winding made of enamelled copper wire can also put solenoids out of action.
However, in order to reach the two shutter magnets on the Canon T90, the camera has to be disassembled deeply. An effort that is not always worth it.
Cleaning or replacing defective solenoids
is often made difficult by the fact that they are installed deep inside the camera and require complex disassembly (and reassembly).
Sometimes, however, they are easy to reach, such as with some Canon A cameras, where only the base plate has to be removed to gain access.
So even with high-tech SLRs such as the Canon T90 or Minolta 7000 AF, these are not electronic problems, but simple mechanical ones that could easily be solved if these SLRs were not built so tightly.
For us DIY repairers
this means that we need less knowledge than electronics engineers to carry out a repair, but rather skills and practice in disassembling and assembling electronic SLRs.
Tutorials can help and invite you to tackle such repairs
Canon T90: Cleaning the mirror magnet
I have a T90 here whose mirror magnet no longer works. The usual symptom of a quiet clicking sound and a flashing arrow in the display occurs. The recommended cure of removing the front cover and activating the - easily accessible - magnet with a magnetized screwdriver tip works with patience...
www.photrio.com
Minolta (Maxxum/Alpha) 7000 AF: Tutorial for removing the mirror box and shutter unit, notes on assembly
In order to access the shutter for repairs or replacement, the mirror box on the Minolta 7000 AF must be removed. The same applies to fixing problems with the aperture control or the mechanics of the mirror box. This tutorial shows the necessary steps. The basis for this is the Minolta Service...
www.photrio.com
+++
All information provided without guarantee and use at your own risk.
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