HI Jamie--

Did you remember to lower the valve at the top--the one that you open up 
to remove the source? 

If the "spring" on the side is not lined up or springy, and gas won't be 
funneled into the source.  If you put the metal spring on backwards, it 
won't push the metal piece out properly.  Also make sure the transfer 
tube is doing ok too.

Also, inside the flight tube, the source pushes up against a cage.  If 
that is bent, you may have to repair/replace it.  If does come out (at 
least it did on our 253).

good luck.

gerry

Jamie Elsila wrote:
> We're experiencing a sensitivity drop with our MAT253 and I was hoping for
> some advice.  I know other people have recently asked about similar
> problems, and I've found the responses helpful, but we still have a problem.
>
> It's a relatively new instrument and we just changed the filament last week
> for the first time.  We had to reseat the source a couple of times after
> that because of a short in one of the wires.  Now, we're getting a signal
> intensity that's about half of what it should be, both with the dual inlet
> and through the Conflo.
>
> We're a little worried because we think that at least one of the times we
> put the source in, we didn't have the pin and notch lined up properly, but
> we tightened it down anyway.  Our Thermo technician says this could have
> bent the support rods, but that if that were the case we'd most likely be
> unable to get it to seat correctly now and would be getting almost no
> signal, rather than just a 50% drop.
>
> We've checked the new filament and it looks correctly centered.  Our box and
> trap are at 0.9 and 0.6. I know they should be closer to 0.8/0.7.  What
> could be causing this, and could it be the cause of our sensitivity drop? 
> We've done a lot of checking of the tuning, both using the autofocus and
> manual focus.  All of the settings seem to respond, and we've checked the
> leads several times, so we think they're okay.
>
> We know that the position of the source is important.  At one point, we know
> we had the pin and notch lined up correctly, but were getting about a 90%
> drop in sensitivity.  After reseating the source, we got to the point we are
> now.  We could keep trying to reposition the source, but at some point the
> numerous iterations start to feel futile.  I'm willing to keep trying, though.
>
> Any ideas would be greatly appreciated.  Thanks!
>
>