Re: JEOL 6400 Objective Lens Repair
- From: Gary G <see.signature@bottom>
- Date: Sun, 24 Apr 2005 08:22:08 -0700
On 24 Apr 2005 00:37:16 -0700, "Aniruddh" <aniruddh_sarkar@xxxxxxxxx>
wrote:
>Hi,
>
>Our 1990-purchased JEOL6400 SEM 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 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!
That is an unfortunate situation. The coil is usually inset from the
column such that a short to it is inlikely. The coils I have seen
have to path to ground, as wound. If yours does, it is different. In
any case, you might try to stip the assembly down and isolate the
short or path to ground and see if this can be repaired. Make sure
that any local cooling pipes have not corroded and leaked into the
lens.
If your scanning system is still working, you should get an image
without condenser on or connected. This would be like extreme low
condenser current--wide probe. For traditional SEMs with a final
aperture, it ought to work this way.
Have you tried another 24V PS? As supplies age, their electrolytic
caps tend to dry out and cause all sorts of problems. Replacing the
aluminum caps or the whole PS fixes this. Have you tried to get a
replacement coil from JEOL? Probably a huge pain.
Gary Gaugler, Ph.D.
Microtechnics, Inc.
Granite Bay, CA 95746
916.791.8191
gary@microtechnics dot com
.
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- JEOL 6400 Objective Lens Repair
- From: Aniruddh
- JEOL 6400 Objective Lens Repair
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