Sensitivity Loss Help


I was hoping someone could provide some help/suggestions.  We recently experienced a 75% sensitivity loss, and we're not sure how to fix it. We have a 7890AGC-5977B MSD.   It began with a "no emission current" message, and I replaced both filaments.  This is when the sensitivity loss was first evident.  Figuring the new filaments were bad, I replaced both filaments again, and the problem was fixed.  However, a few weeks later, we ran some unknown/dirty samples thru the instrument and damaged the column.  We replaced the column ( DB-1MS UI) (old and new column are the same type).  Following the column change, the sensitivity again dropped around 75%.  I have changed the gold seal, liner, septa, cleaned the source, changed the pump oil, replaced both filaments again, and nothing has helped.  The air and water check was normal.  One thing I did notice was when the instrument was performing well, the "gain factor" on the etune printout under "ramp criteria" was around 1.  When we lost sensitivity, the gain factor on the printout is always above 3 and sometimes above 6.  The gain factor for our actual methods is 1.  I'm not sure what is causing this.  Any insight would be greatly appreciated, as I am not that experienced with troubleshooting these instruments.  Thanks!

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