First I would have checked the reference gas pressure and carrier pressure.
Then I would reset the ion source settings and autofocussed once again. If that doesn’t help, then I would try a magnet scan.
Finally when nothing of this works but there is some light in the tunnel (signal), I would leave the instrument in endless zero-enrichement test, grab a hundred cups of coffee and return after a day or two. If this doesn’t help and you have dismantled, washed the source properly, “remantled” (is that a word?) and checked and rechecked the source, I would call Thermo.
I recently cleaned the source in our Delta V Plus. I also replaced the slit which was quite eroded. On reinstalling the clean source, the sensitivity for both C and N is about a quarter of what it used to be. I’ve tried three different filaments, including the one that was running happily before the cleaning, all with the same results. I’ve tried manual tuning but I don’t get results any better than the auto-tune does. I’ve disassembled and reassembled again checking each ceramic piece and lead. The extraction plates are oriented correctly. The stability of the diminished signal is very good (standard deviation ~ 0.02). We’ve cleaned the source previously with no problems.
Does this problem sound familiar to anyone? What might I be overlooking? All suggestions are welcome.