(Aniruddh Sarkar) writes:

Hi,

I am not very sure whether this is the best suited forum for my query
but still I am sure this is not totally off-topic. So here goes..

Our 1990-purchased JEOL 6400 Scanning Electron Microscope recently
developed an intermittent problem of black bands randomly
appearing/sliding on its display.

This was traced to an oscillating 24V supply powering, among other
things, its objective lens control board and the objective lens
itself. We found both ends of the objective lens (basically an
elaborate coil of insulated copper wire wound on a conical steel(?)
core) winding were at ~1 ohm to the the instrument chassis while the
coil itself ~2ohm across.

Disconnecting the lens has stopped the supply oscillation etc but
ofcourse now there is no image!

We are guessing that either the condensation due to the running
cooling water or the heating due to lack of it has shorted the
innermost layers of winding to the core.

While we are still hunting for a spare, I would like to enquire people
here for pointers on design & rewinding of electromagnetic lens coils.
The winding looks specially designed - with number of turns decreasing
in each layer in a particular fashion as one goes up the core.

Will just replicating the winding - wire gauge & the turn pattern -
bring it back to function?

While I'm not an expert on SEM design, there is no magic involved.
Replicating the coil as precisely as possible should restore function.
It certainly can't hurt while you search for a new coil.

Roughly how many turns are involved? Is this something you could do
with a manual coil winding machine or by hand?

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