At 11:46 AM 2/5/02, you wrote:

>I think the problem is that the current going into my filament starts to
>increase but then trips off some how. The current J48-P48 should be ~3.8
>amps but I am registering 0.252 mA. I have been told that the problem is
>with the filament and I have been instructed to replace the filament once
>more.
>
>My original source supply has since been tested in another machine & worked
>well. So the problem does not lie in the source electronics and I doubt
>very much that it has anything to do with the filament.
>
>I would be interested in hearing any comments/theories about what may be
>happening with my machine.

Have you checked the trap current? This can be measured at J/P17 and should
be around 0.8mA, depending on where you have yours set. It is set on the
little recessed trim pot in the source control panel. I would assume that
the emission light only comes on if this is in a certain range. Since the
LED is coming on, then the trap is seeing a flow of current from somewhere,
right? Perhaps its a badly alligned trap, or its shorting out on the source
body. Did the source ohm out OK?

You can also check the source current between J/P13. This should be the
same, ~ 0.8mA. I think this one is reading the current due to the electron
flow from the filament that isn't reaching the trap.

This is from the notes I have at my training course in Ottawa. While the
course/instructor were very good, I don't take the best notes or have the
best memory at times, so anyone with more detailed and/or correct info
please chime in. The more we all understand about this, the quicker and
more easily we can keep our instruments up and running.

Howard

Howard Sanford
919-513-3039
North Carolina State University
Dept. of Soil Science
Box 7619
3114 Williams Hall
Raleigh, NC 27695
http://www.soil.ncsu.edu/