Originally posted by reh321 I have now had my K-30 for 37 months, roughly 3100 on the shutter count. I took ten or so pictures last Saturday; today, after roughly five days rest I took a picture of our cat resting on the piano - first image was black, second {allegedly same settings} was OK. "Folklore" suggests that these cameras don't like time off. The five day rest mine had took one shot to recover from; the longer one yours had was more of an issue. I'll see whether mine needs less rest, or more "warmup"/"recovery" over time.
My theory , ...... normally (mostly) solenoids consist of a metal armature & a coil and return spring such that when the coil is energized it becomes an electromagnet and pulls the armature to the coil. When the coil is de-energized the spring returns it to it's resting position. ( there are other configurations but lets keep it simple). This is fairly straight forward and easy to understand. With the K30 solenoid in question it seems that the resting position of the armature is held in position by a permanent magnet and the energized coil repels the armature against the magnetic attraction of the permanent magnet (ie.opposite magnetic polarity), now if a piece of metal (Iron) is in contact with a permanent magnet some magnetism will be transferred to to the Iron. In this case the armature, this magnetism builds with time and will be of the same magnetic polarity (ie. same attraction). The act of energizing (operating) the coil to create a reverse magnetic field also demagnetizes the armature and maintains a balance. This is why.....
- its always the first frames that are dark - as the armature has been at rest and the magnetism has been building, then you fire off some shots and the demagnetizing effect on the coil operation comes into play and the solenoid starts working again - until the camera is at rest for some time and the magnetism builds up in the armature again.
- this may also explain why some people report differing results with batteries of different strengths - due to stronger energizing / demagnetizing pulse.
- the fixing procedure of filing the ends of the armature or using a spacer is all to do with reducing the transfer of magnetism from the permanent magnet to the armature.
Demagnetizing the assembly using an external demagnetizing wand was something I was beginning to look into ( if only I could have found my old CRT TV screen degausser
) when I remembered I had taken out an extended 5 year warranty and was able to get my K30 fixed under warranty (replacement solenoid).
So I would suggest the original solenoids had a magnet that was a little to strong or the spacing of the armature in the resting position a little off, or the energizing pulse a little week, or maybe even the composition of the armature material allowing it to absorb more magnetism, or perhaps a combination of factors. Certainly a difficult failure mode to predict !