Servicing binding fresnel focus adjustments

[Marc Roessler]

Hey guys,

I own an older, small Quartzcolor/Ianiro/Rank Strand tungsten fresnel unit (Type "Mizar", 300 to 500 Watts).
It has a little problem: the focus adjustment is jerky and tends to bind, especially once it gets hot.
The focus gears seem rather crude, you can see them here in the second image (not my unit, but same model):
https://www.tuttofoto.com/ianiro-minispot-mizar-500-8982645+d-37171--it.html

Any suggestions how I can restore this to full working condition? I'd especially be interested in suggestions around which (high temperature) grease to use - preferrably something commonly used in the automotive sector. (Obviously, neither petroleum jelly nor WD40 are an option...)

Best, Marc

Edited January 1 by Marc Roessler

[Mark Dunn]

This looks like a twisted screw (like a corkscrew) going through a shaped slot? If you can dismantle and clean and polish the screw and slot, and the rack on which the bulb travels on its two rods, this will help. I don't know about grease, but there's no sign of it on that photograph.

[Marc Roessler]

Some Updates.

The "corkscrew" looks fine, the grease is still smooth and does not stick. The actual problem turned out to be the slide tilting sidewards and then binding to the guide rails (top and bottom in the attached picture). In the picture, you can see the slide already is at a slight angle, not perpendicular to the guide rails. This is it enough for it to bind. I took out the (already quite clean) guide bards and slightly polished them using a cloth (there wasn't any grease grease on them). This improved things, but a slighty "bindy" feeling is still there.

I'd say this unless the slide is worn in a strange but subtle way (no easy way to check...), this seems to be somewhat of a design issue. If you have Mizars with similar/without problems, let me know, would be interesting to know.

[Marc Roessler]

However, ironically, I ran into a "sticky focus" issue on another unit: on a Quartzcolor/Rank Strand Castor 2kW fresnel.

There, the focus is hard to turn, it seems the grease got too gummy. The grease is a silvery/grey paste that can only be cleaned using break cleaner, not using rubbing alcohol. The grease is on the guide rails and on the pulley. Same question here: does this grease belong in this place in this unit? What grease to use to renew this?

Edited Friday at 03:13 PM by Marc Roessler