I have some problems with my MSD 5973 (diffusion pump). Nitrogen was between 10-18% and EMV between 2400-2600. I bought supplies and i did a maintanance: I changed He trap, MSD column Nut and ferrule, diffusion pump oil, filaments, interface, analyzer, PTFBA valve and vent valve o-rings.
The first days, my EMV decreased to 2100, however, it increased to 2400 again, and N2 maintain between 10-18%. I isolated the MSD and it continued with high N2. I used air duster for checking leaks and i didnt found.
The vacuum in ion gauge is 1.0x10 -5 with 1.1 mL/min of He flow. When I start the manual tune, 69 219 and 512 abundances decrease a lot (30% aproximatly) and it stabilizes. When I start the manual tune with PTFBA closed and later I open it, N2 abundance decrease 15%.
I think that PTFBA valve has problems. Any recommendation or what other problem can it be?