5971 broken quad support - what to do?

[jkloepping]

I've been having some problems with tuning on a 5971. Finally, having swapped all boards, electron multipliers, checked connections, reinstalled software, and many other things, I took the mass analyzer apart. I found that the ceramic quad support on the source side has a quite fragile "nose" that protrudes in to the mass analyzer. Two rather large broken pieces were floating around in the analyzer. I have a spare, so I replaced the part and I'll see over the next few days if that fixed the problem.

My question is, what is the purpose of the nose on the support, and what would be the harm if the nose was left broken? The purpose cannot be quad support, because that is provided by the outer ring of the insulator. I assume that it prevents ions from migrating to the outside of the quad?

[James_Ball]

That would be to prevent the Entrance Lens from scratching the quads when the ion source is inserted. The Entrance Lens protrudes slightly into the quads and could damage the thin silver tape that forms the quadrupole. Those chips laying inside the quad would interfere with the EM fields and probably caused the problems. Also a common problem on 5971/72 quads was de-lamination of the silver tape at the very ends of the quads. If this happens it looks like a mouse has been nibbling on the tape at the ends of the fused silica of the quad. Once that happens they are pretty much toast.