A couple things to check that may seem obvious but have stumped me in
1. Are all the focusing plates oriented correctly? The four ceramic
prongs on the source are space evenly apart and will allow for a 90
degree misalignment. Once reassembled, you really can't tell that
there's a problem unless you look right down the front of the source.
2. When you checked for shorts, did you compress the source? The leads
that power your focusing plates and the filament are very close
together, they may not be shorting when the source is outside of the MS,
but when installed (compressed) some of them may be touching.
The IRMS was running up to spec. before the cleaning? or were you
experiencing any problems that prompted the filament change?
Best of luck
Iso Geo Chemistry Lab.
On 5/20/2011 1:57 PM, Lucas Mead wrote:
> Dear Isogeochemists,
> I am struggling with a problem that has been posted a few times in the
> archives. After a source cleaning and filament replacement I have lost all
> signals on all three cups of my Delta V Advantage (tied to EA via Conflow III
> for C& N). I have tried numerous times to re-seat the source, I’ve replaced
> all ceramic pieces, replaced the quartz spacers, substituted out new
> filaments, and checked for continuity and shorts. Current stats with the SGE
> valve open are: HV=3.07KV, Box=0.9mA, Trap=0.57, Vac=1.7^-6; with the
> SGE closed the vacuum goes to 2.6^-7. Magnet scan (3000 to 15000 steps)
> with CO2 flowing shows no peaks>1mV. I checked and the magnet voltage
> varies as the scan progresses. Varying the focusing parameters also has no
> effect. Voltage registers momentarily in the cups when SE-Supressing is
> lowered or the few seconds after the source is turned off. I’ve restarted the
> computer after all changes and checked that the input cables were well
> seated. This situation has me stumped; I’ve dealt with low signals before but
> there appears to be nothing entering the cups for me to work with. Any
> suggestions would be greatly appreciated.
> Thank you for your time,
> Lucas Mead
> University of Hawaii-Hilo, Analytical Laboratory