Originally posted by Cee Cee Just my take on what's happening here..
The coil assembly has a fixed magnet which keeps the armature engaged, energizing the coil creates an opposing magnetic force which allows the armature to be withdrawn. Over time the armature retains some residual magnetism, it reaches a tipping point where the magnetic field produced by the coil is no longer strong enough to overcome the the combined force of the fixed magnet and the magnetized armature and allow the armature to be released.
Maybe there is a different use of names for that part which is released when the solenoid actuates:
It is the
plunger which is released/withdrawn (the name
horseshoe because of its shape was used by myself long time ago)
The
plunger sits on the
armature which itself does not retain any measurable magnetism, it is to far away from the magnet.
The amarture is held by a spring which acts when the plunger is released.
This is important because we need a precise language here. As soon as I realised that the name plunger is the best I started to use this one.
I thing this is sensible and helpful to everybody.
It is only the plunger which magnetises due to the fact that it sits right next to the permanent magnet when the camera is not in use, i.e. 99% of its live.
Originally posted by Cee Cee The action of activating the coil produces a reverse magnetic field to cancel the fixed field, this also has a demagnetizing effect on the armature, so firing shots in quick succession demagnetizes the armature and puts it the other side of the tipping point and the camera starts working normally again.
At the beginning, yes, but sooner than later the camera does not work anymore, all photos are dark (exept full closed aperture)
Originally posted by Cee Cee Left alone, the armature will again be re magnetized and will fail again.
The plunger, not the armature (depending of course how you intened to use the name/word)
Originally posted by Cee Cee The issue I believe is that the manufacturer of the magnetic solenoid changed the magnetic structure and upset the balance
No, the manufacturer did not change any structure. The manufacturer moved production from Japan to China. The manufacturer was no longer the manufacturer and most important, didn't even tell Ricoh that production had changed.
The solenoid was from now on manufactured in China with complete new materials but same form and supposed same function.
New materials are:
- magnet
- alloys
- PET body instead of PTFE
It is not a "magnetic solenoid" but a solenoid, in this case with two different type of magnets, a permanent magnet and a field-coil electro-magnet.
Accurately it is a
'single direction push' "plunger solenoid".
Originally posted by Cee Cee Filing the armature can work because it reduces the coupling to the fixed magnet and slows the build up of residual magnetism.
It can work but it damages the surface of the alloy and thus invites corrosion.
Also filing has led to
- same problem occuring again
- opposite problem: overexposure, the plunger remains open sometimes/often/all the time
Originally posted by Cee Cee I'm not sure that degaussing the armature will work long term, at best it could only return to it's natural state which will make the camera work but the problem will eventually re occur, as the core issue of the magnetic structure of the coil assembly hasn't been addressed.
Degaussing is useless, the plunger demagnetises after a relative short time but magnetises very quickly due to its alloy-mix and due to few other important factors:
- stronger magnet/holding force
- weakening of the PET which acts as a bearing for the plunger which "shoots" out with quite some force and thus due to:
- more tolerance between plunger and PET body..... which allows the plunger to be stuck because it can tilt to left and right
By now I had many green solenoids (new and used, filed and treated with other methods) in my hands, inspected them closely mechanically, electrically and "close up" with my precise old fashioned microscope (which does not allow me to take photos, I regret).
I have worked for decades with something quite similar because I repaired and installed "moving coil phonocartidges" (and to a lesser degree "moving magnet" and "moving iron" cartridges) I had to stop with this work due to "aging" eyesight but know enough about it because the pentax solenoid is kind of a rough diamond compared with those very fragile and super presice devices. Or we could say a Pentax solenoid is a tractor when a v.d.Hul or Benz or EMT cartridge is a sportscar.
I also had the chance to compare many Pentax used early SLR and late white Japan made DSLR solenoids
as well as several "replacement China-Solenoids".
Originally posted by Cee Cee If you wish to experiment then try the other solutions and see, but if you just want to fix the camera then I think changing the coil would be the best solution.
Indeed, and particular on the K-70 I would not take the risk of
cobbler-solutions when a nice prober one is obvious and not really expensive.
If I take on this work to disassemble my Pentax (which already is quite some work) then to sand/file/grind or worse, to lube is kind of throwing pearls in front of swine.
Those who do it have often just the shortsighted intention to sell their bodies as "100% working" which is ... after all... cheating the buyer, i.e. similar as selling a car which has a damaged cylinderhead-gasket and just cleaning of the foam and changing motor-oil.