My first call would be to the manufacturer of the SEM. If that fails,
then I guess you are stuck with rewinding the coil. But, it will be a
long and arduous process. You will have to photograph the old coil and
take many notes to be sure you replicate it correctly. Also, you must
get exactly the same wire and insulation, so that the number of turns
of wire are the same for each layer as in the original coil. But, that
means the wire may be subject to the same shorting problem as you are
now experiencing, so you must find the source of the problem (water
leakage ?) before you install the rewound coil. Altogether, this
sounds like a MAJOR problem. I would exhaust all other possibilities
before starting to rewind the coil.

H. R. Hofmann

Aniruddh Sarkar wrote:
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?

Any info/pointers highly appreciated!

--
tia,
Aniruddh Sarkar
Research Associate
Dept of Electrical Engg
IIT Powai
Mumbai, India