HI Herb--

Just a note--vintage computers may have vintage power supplies, and low power/voltages than spec, so can also cause some problems.  Sometimes changing slots for the fiber optics card can also help--or even just re-seating boards (removes a wee bit of corrosion that may have built up).

If you haven't, double check your open splits--make sure all are positioned properly.  I take it the sensitivity issue is seen on both the sample and ref gas sides, and you haven't changed/bumped the sulfur window knob.

Have/can you check absolute sensitivity?  And was the recent sensitivity seen before you fixed the problems higher than usual for the instrument?  Just wondering if previous setup was getting into some funky tune space--but looking ok on the display.

take care,


p.s. For newbies:
If you open the source and lose sensitivity (after retuning), you may  just need to wiggle source to get the holes for the gas transfer from the valves to the source to line up.  And of course, you may have a connector that popped off.  When Isodat let you control each plate independently, instead of the avg voltage and difference between plates, you could see if adjusting a given plate would affect the signal.  If it didn't, then that connector could be loose. 

On 1/28/2016 12:19 PM, Herbert Tobias wrote:
[log in to unmask]" type="cite">
Hi All,

Thank you for all your comments.
Just for ISOGEOCHEM record, I wanted to update the SOLUTION to the situation with our MAT253, which had an issue with ISODAT randomly turning on the heaters (not necessarily initially) and venting.

Upon pumping down at one point, I made sure the computer was OFF, and the system was stable for couple days.
Then I decided to turn computer ON, and start ISODAT. At that point the computer had a fault, basically according to computers error codes, it was the memory module/sockets. Tried to remedy by switching out other RAM memories to no avail. (Motherboard fried?) 

Therefore, I setup the ISODAT and associated cards in another similar vintage computer (XP), and got the system working fine. So it doesn't randomly turn things on now.
However, now the sensitivity of the IRMS is 2/3 of before this issue. That's workable for now.  I did try to retune a bunch of times with little change. Any ideas? I loath to open source.

Anyway, the deal probably was that the motherboard was acting up, causing ISODAT to work funny.


On Thu, Jan 21, 2016 at 6:13 AM, Dijk, A.E. van (Arnold) <[log in to unmask]> wrote:

Hi Herb,


I had something similar a year or two ago. Burnt my elbow on the analyser. Now I have the switches on the plugs in off position until I want to roast and not ISODAT.

Around the same time I had a problem pumping the system. That was due to the detector housing vacuum. When you start to pump with the detector vacuum in FV position push the pan hard so there is contact with the O-ring.






From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of Herbert Tobias
Sent: 19 January 2016 23:37
To: [log in to unmask]
Subject: [ISOGEOCHEM] MAT253 heaters


Hi all,

Just recently our 253 has vented on its own a couple times in the last couple days. Apart from doing a bunch of pump maintenance etc, we noticed that upon rebooting and opening Isodat 3.0, it now automatically turns on the heaters. After a few hours it presumably vents because pumps are too hot. Anyone else experience this?


Dr. Herbert Tobias
Sr. Research Associate
Division of Nutritional Sciences
244 Garden Ave
Cornell University
Ithaca NY 14853