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04-23-2020, 01:02 PM   #46
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A lot of hot air about something, that already has been solved.

04-26-2020, 07:12 PM   #47
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QuoteOriginally posted by photogem Quote
A lot of hot air about something, that already has been solved.
well with CV19 being what it is I have some time on my hands to consider these issues and expel any unwanted gases !

come on, don't you want to fully understand the science here, after all this could possibly lead to novel solutions which don't involve having to track down an old camera from which to remove the solenoid and then replacing the solenoid in their own camera, which involves de-soldering & soldering the coil by people with no soldering skills, which in my experience doesn't always end well.
Do you find it interesting that the "filing the edges of the plunger technique" (to reduce the contact area) has had varied and inconsistent results, perhaps the inconsistency is more to do with which polarity they refitted the plunger! rather than the filing technique.
I must admit the finer points of magnetic theory are perhaps above my pay grade, But reversing the poles on the horse shoe plunger should counteract any residual magnetism, and perhaps provide a simple solution, if not then residual mag (as the primary issue) could be eliminated from the discussion and other theories explored.
04-28-2020, 02:00 AM   #48
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Thank you for your reply Cee Cee.

I believe the problem with the Chinese solenoid is that the plunger material is of relatively higher coercivity material than the Japanese one (ie it retains its magnetism after the field strength is removed). Reversing the plunger wouldn't work long term as the plunger would just get re-magnetised.

Low coercivity material such as soft iron (low carbon) is very easily found, cheap, and machining a few plungers simple- and far easier than dismantling otherwise good cameras. What a great pity Pentax didn't catch on earlier, for almost no increase in production cost the issue would have been obviated.

Malcolm (Chartered Electrical Engineer with Nuclear Electric)

PS But others may know better of course!
04-28-2020, 06:17 AM   #49
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QuoteOriginally posted by malc77 Quote
I believe the problem with the Chinese solenoid is that the plunger material is of relatively higher coercivity material than the Japanese one (ie it retains its magnetism after the field strength is removed). Reversing the plunger wouldn't work long term as the plunger would just get re-magnetised.
it will be interesting to see how you get on, good luck. If it took 5 years for the build up of magnetism to cause the camera to malfunction (in my case) then by reversing the plunger it could take a further 5 years to build up to that point again - by my simple logic. But this is, of course if residual magnetism of the plunger is indeed the only problem.

04-28-2020, 02:48 PM   #50
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QuoteOriginally posted by Cee Cee Quote
.....come on, don't you want to fully understand the science here, after all this could possibly lead to novel solutions which don't involve having to track down an old camera from which to remove the solenoid and then replacing the solenoid in their own camera, which involves de-soldering & soldering the coil by people with no soldering skills, which in my experience doesn't always end well.
QuoteOriginally posted by Cee Cee Quote
Do you find it interesting that the "filing the edges of the plunger technique" (to reduce the contact area) has had varied and inconsistent results, perhaps the inconsistency is more to do with which polarity they refitted the plunger!
As I have written HERE there is no chance that turning the plunger would have any other effect than losing its magnetism but not because of it being turned around but because it was away from the magnet and lost remanence.


QuoteOriginally posted by Cee Cee Quote
I must admit the finer points of magnetic theory are perhaps above my pay grade, but reversing the poles on the horse shoe plunger should counteract any residual magnetism, and perhaps provide a simple solution, if not

a) then residual mag (as the primary issue) could be eliminated from the discussion and

b) other theories explored.
a) is a very good idea because there is no reversing of poles on the plunger possible

b) is not really necessary, we don't need endless theories but only facts and facts are "on the table"

And we have a reference:
The white PTFE Japan-Solenoid.
It never failed.

As I have shown in my report about the history of solenoids built and used by Pentax and particular that one used in the Pentax K-70:
Ricoh tried to do the best and it for sure became better but not perfect.
(My own K-70 had failed and I had a second for repair)
And this report will answer your other questions about sanding etc.
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