Dear Arnold,

We have an Isocarb that is about five years old, and I agree that the
stepper motor is one of the things Micromass could improve. Our isocarb
transfers movement by means of two thooted weels, that sometimes fail,
causing severe saking of the carrousel and not advancing it, so missing
a position.

When I mentioned this to VG people, they told me that now they have 
belt-driven motors that will make smoother movement of the carrousel. What
sort of transmission does your Isocarb have?

In any case, the carbonate powder you see in the base plate of the isocarb
could also be due to too fast pumping on initial evacuation. Make sure
that you pump for long enough time through the capillary before opening
the carrousel directly to the rotary.

I do not know a good reason to choose between metal and glass buckets, but
I do noknow that the buckets they had when the Isocarb was originally
developed were metal ones. Shortly after they changed to glass onbuckets
(we use these), and apparently they have gone back to metal lately.

Many of the problems we haved with the Isocarb were solved by an Ex-VG
engineer, Paul Hanson. He works now in pPortugal, but I'm sure he can 
still be contacted via Micromass.

The Isocarb is an excellent device ... when it works!

Best luck,