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Topic: Eumig Mark S 802: drive discs & bulb
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Richard Gordon
Junior
Posts: 19
From: London, England
Registered: Nov 2009
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posted December 10, 2009 05:24 PM
Hi John, thanks for your advice. All I've done, since my original post, is to use cotton earbuds soaked in propanol to clean the drive ball and the forward and reverse rubber discs. The projector is now running reliably (so far!). Regarding the sensitivity of the drive to the thickness of the discs, it's not clear to me whether it's the thickness or smoothness of the rubber that's the controlling factor. This projector has developed indented tracks along the 50c/s 18 and 24fps positions. If I switch the ball to the 60c/s positions, which don't have indents, the projector runs more reliably. This could support both the thickness and the smoothness theories. On the other hand, other threads on this forum have reported success with sanding with very fine emery paper; simply to provide a surface with a better grip. What's your view on my "superglue" suggestion? It would increase the thickness! Regards, Richard
[ December 11, 2009, 03:31 AM: Message edited by: Richard Gordon ]
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frank arnstein
Jedi Master Film Handler
Posts: 534
From: Gold Coast. Australia
Registered: Jan 2005
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posted January 28, 2010 07:03 AM
Hi Martin
Thanks for the response but I don't think you have grasped fully what I tried to explain about setting the eccentric motor pivot.
I was not talking about a centre line between the 2 discs at all, although that is also an important line to aim for when setting the forward & reverse to be equal.
I was talking about another important line.
By moving the eccentric mounting up & down, it also moves the ball back & forth on the disc that is being currently driven. As long as the speed fork remains in its slot, it will still do its job of sliding the ball along the surface of the disc, varying the output speed. The thing to realise, is that when you lift the mount up, the ball will also move away from, or toward, a vertical line on the driven disc at its widest diametre. This center line is where the ball will spin the disc most easily in either direction because there is no side forces to make the ball skid. The ball will roll cleanly instead of rolling and also skidding. A skidding ball won't drive properly due to friction slowing it down.
Do not confuse this line with a central point between the 2 discs.
I also did say to ensure it works well in both directions, have another read.
You said....
"It's probably also true to say that if the parts are all original and the paint sealing those screws on the rear pivot mount is unbroken the ball will still be in the original factory position...i.e. correctly placed."
I don't think this is neccessarily so, after much use and time.
When I encounter this problem, I adjust the pivot mount & break the factory paint seals. They drive Ok after correct resetting.
AND this
"Also, adjustment of that eccentric pivot mount has another (often overlooked) function.... making sure that the fan, which is located in the casting below the motor, does not foul on the casting. The clearances are very small; if the fan is not located exactly right on the motor shaft.
I don't believe the eccentric adjustment is to provide this fan clearance, as if you were to move the drive ball away from the sweet spot on the vertical central line, the drive from the ball to the disc would be upset & speed loss will result immediately.
Dogtor Frankarnstein ![[Smile]](smile.gif)
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At Projector Heaven the Focus is always on Detail.
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[o:/o]<|=- dogtor@projectorheaven.com.au
//``\\
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Martin Jones
Phenomenal Film Handler
Posts: 1269
From: Thetford , Norfolk,England
Registered: May 2008
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posted January 28, 2010 08:54 AM
There is only one correct alignment point, the point at which all the parts (ball,discs,motor shaft speed fork) are in the correct relative positions, and that point is established at the factory by means of the adjustments provided. And that point is achieved with new,"perfect" components. Wear on those components will cause the interaction between those parts to gradually become ineffective, but the alignment between those parts will always be the same as long as the alignment adjustments are not interfered with.
As the parts wear, the mechanism is substantially self adjusting; it is only required to ensure that it provides sufficient pressure between ball and discs to provide reliable drive. Your "sweet spot"/ "sweet line" remains exactly where it was set, unless the pivots (shaft or bushes or both) become worn.That is easy to check; if they have no play, the original "undisturbed" adjustment holds good. If they are replaced because of wear then the adjustment needs re-doing.
There are a number of factors that can affect that drive reliability, ignoring friction elsewhere in the machine....
1. The condition of the disc rubber, both in terms of surface shine and thickness. That has been dealt with many times.
2. The surface of the ball. As that is highly polished "as new" becoming "more polished" should have little effect.
3. The interaction between those two components, governed by whether the ball can physically move into contact with the disc and whether there is sufficient, but not too much, pressure at the point of contact between the parts to duplicate the original conditions.
As said earlier, the self-adjustment which compensates for dimensional wear of both ball and disc rubber is already built into the machine, provided by the spring that enables the motor to tilt further until the pressure is sufficient to provide the drive, but only if the stops are correctly set to allow it.
Interestingly, Frank, I can't recall a post where you have commented on the function of these components. If you have, perhaps you could point me to it?
What I do know is that I have recently been involved with the conversion of a S710 (same mechanism) for telecine purposes, and faced with the same drive problems where both the disc rubbers and the ball were in virtually "as new" condition and having tried all the usual suggestions (including your "eccentric mount" adjustment) I finally solved the problem by replacing the "motor tilting spring" with one from my stock of new tension coil springs, selected for the correct tension for the job.
And yes, I did miss your reference to "both directions".. remiss of me.
Martin
[ January 28, 2010, 10:25 AM: Message edited by: Martin Jones ]
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Retired TV Service Engineer
Ongoing interest in Telecine....
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Tony Stucchio
Jedi Master Film Handler
Posts: 625
From: New Jersey
Registered: Dec 2005
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posted July 26, 2010 07:50 PM
These models of Eumigs, with the rubber disc drives, were great machines in the '70s, but unlike belt driven systems, once they wear down they are essentially dead for viewing sound films. (You won't notice the speed issue on silents.) Phil Johnson was selling replacement discs for a while, but they were something like $250. You can get a full projector in great condition on eBay for less -- which is your best bet if you really love Eumigs. But trying to revive one is time consuming, frustrating, and darn near impossible. You will get it to run fine for maybe a few films (which is what happened to me), maybe a week, or maybe a year (as Gary said), but after that, fuggettaboutit!
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