Marco 101 maintenance - power wheel issue

[Uilleann]

This one's new for me, though I have to guess not too uncommon. I've got a relatively new Marco 101 that's developed a very loose power wheel. It won't stay put when reading a lens, and continually rotates forward all the way to the end of the + power band (where it finally stops with a disconcerting clunk". I'm not on this machine anymore, and it was just reported to me last night - so no idea if it was a gradual thing, or how long it's been like this.



For those who may have encountered this in the past, is this a relatively easy fix? Loose Allen screw somewhere perhaps? Power still reads correctly, and the wheel feels solid against the spindle, as best I can tell at least. We can't get ahold of our regular ophthalmic tech to see if he can get it fixed up for us. So hoping it might be something simple I can attempt in house myself. Would love any direction yinz might have.

TIA!

[Uilleann]

Just a bump for a second try. I can't imagine it's much harder than tightening an Allen screw somewhere perhaps, but unsure which one to poke at, and if it's under a cover or anything. Seems this would be rather pedestrian...or should be. No one on the boards anymore with basic maintenance experience with these ubiquitous tools?

[optical24/7]

I’m not used to Marco, (I’m a vertometer man). But you said it reads correctly, so it’s not the outer wheel set screw. You’ll need to pop the hood and see where the power drum shaft is going and follow that to wherever the problem is located.

[HarryChiling]

Sounds like it's the collimator, I'm not sure exactly if the Marco has a lead screw or rack and pinion, but if you remove the back cover then adjust you should see the drift. Often not a screws or anything like that, just needs to be regressed, use a thick lithium grease, use a darker grease since this is collimated light and you don't want any bright grease like a white lithium grease creating reflected light internally.

[HarryChiling]

If it's rack and pinion and you notice the rack is slipping low with very little friction with the gear. You could loosens the screws on the rack and readjust, move the drum to both extremes and adjust so their is some tension. When your done you may need to recalibrate the drum if you mess with the rack.

[HarryChiling]

You may have to remove the drum to get access to the collimater cover screws as well, if you do just mark the drum and dial to rough it in when dome and do your fine tuning afterwards with guagemaster or known lenses +/-6.00 should do the trick.

[Uilleann]

Cool! I *knew* there were experts and old hands still out there that might be able to shed some light! Thanks very much all! Will give it a roll...

[Uncle Fester]

Don't recall seeing the word in my past but the memory isn't what it used to be either
New scrabble word!

What does the collimator do?

collimator, device for changing the diverging light or other radiation from a point source into a parallel beam. This collimation of the light is required to make specialized measurements in spectroscopy and in geometric and physical optic

https://britannica.com/technology/collimator

[Uilleann]

Don't recall seeing the word in my past but the memory isn't what it used to be either
New scrabble word!

What does the collimator do?

collimator, device for changing the diverging light or other radiation from a point source into a parallel beam. This collimation of the light is required to make specialized measurements in spectroscopy and in geometric and physical optic

https://britannica.com/technology/collimator

Fester - if you *really* wanna pull your hair out try collimating a compound telescope! They're an absolute treat. LOL

[HarryChiling]

Don't recall seeing the word in my past but the memory isn't what it used to be either
New scrabble word!

What does the collimator do?

collimator, device for changing the diverging light or other radiation from a point source into a parallel beam. This collimation of the light is required to make specialized measurements in spectroscopy and in geometric and physical optic

https://britannica.com/technology/collimator

Collimator is the back body of the lensometer, that light bulb is converted to parralell rays when it exits the lens stop, then passes through the lens where it is refracted, then enters the prism compensator where it is deviated, then goes through a high powered known lens to a focus on the reticle, the diverges again through the eyepiece which should bring it back into focus with a high plus to a focal point where if you view through the eyepiece the reticle is in focus. That's why the first step in lensometry is to focus the eyepiece to the reticle plane.

[HarryChiling]

The lensometer is a simple but highly effective device due to the simplicity. You can simulate it with an optical bench.