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* I can only speak for the 8200, but the system is probably the same:

At 5/1/2009 03:43 PM, you wrote:

How does this silly thing function normally?  Does the software just
drive it for n-seconds, until it's sure it bumped up against the stop,...

Yep, that's exactly it. There is a slip clutch to keep the gears from shredding.

or does it have some feedback that I'm not seeing?  What bugs me is if
it just drives up against the stops what keeps it from shredding up it's
little gears?  Some kind of clutch?  Does it ever know if it's
misaligned, or what state it's in when it powers up?

I'm not sure about that, but I think if you flip it by hand while the power is off, the computer doesn't have a clue. My guess is that when you do an initalize the motor just cranks in the direction of the crystal that's selected by software.

We had multiple problems with one of them, until the service tech found out that one wire wasn't soldered on properly. Other things can can happen is that it doesn't get to the indent position. That slip clutch has to be loose enough to protect the gear, but stiff enough to make sure the crystal carrier seats properly. Right now I don't have one open to jog my memory, but as I recall there is a little spring (not a coil, but a flat little springy thing) that is supposed to hold the carrier in place, and the clip clutch has to make sure that is flips past it. Hard to describe without using my hands.

Alfred

Alfred Kracher
Ames Laboratory (USDOE)
Iowa State University
227 Wilhelm Hall
Ames, IA 50011-3020
Tel.: 515 294 7097