We have had similar problems which have been solved by momentarily turning off the entire 253 (pumps and all). There is a rotary switch at the back. Rotate it for 1 second and then restore it to the original position. The pumps go off and then come back on but you should not use vacuum. I switch the source off when I do it just in case. We have had to do this 2 times in the past year because of unstable KV. I suspect that there is a failing power supply which gets reset but my enquiries to Thermo have gone unanswered.
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of gerard olack
Sent: Thursday, October 27, 2016 2:33 PM
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] Unstable Signal 253Plus
Did you clean the source a couple of months ago? If not, does it need to be cleaned? ;)
It can be a failing electrical component--but it might be a loose connection. One of the wires may have popped off the source, or the source may not have been tensioned properly when re-assembled (check pins holding rods in place). You can check connectivity (hV OFF!!!) to make sure there are no shorts before taking the source out too. IF one of the heater bulbs fell out, those wires can move a bit and cause a short too.
Not sure if the electronics changed much going to 253+. IF you can peak at the lens control boards, check the LED's and components and look for obvious problems, e.g. a chip blew it's top. The instruments are generally pretty good at handling arc's, but it's possible that one fried a component.
On 10/26/2016 9:45 AM, Marvin Bobrowski wrote:
> We are working with a Gasbench II connected to a 253Plus and since a
> couple of month ago the signal has become very unstable.
> I got suspicious because my linearity for d18O is much higher than
> recommended by thermo (is:0.12 %o/V [should:0.05%o/V]) and every once
> in a while the signal changes over one order of magnitude for a short
> period of time.
> Sometimes I even lose almost all of the signal over night and will
> have to refocus to get it back to where it was before.
> Also, measurements through the dual inlet show an irregular behavior
> leading me to think that there might be a malfunction in the electr.
> control unit or a dirty source and not something in the Gasbench itself.
> We checked water (m/z18 below 1V)and the system seems to be leak-free.
> The filament is rather new, box and trap appear to be stable. We run
> it with a current of 1.5mA
> Did anyone of you have had a similar experience with his/her 253 or
> has heard of a malfunctioning source control unit?