Very strange 5970 behavior

[mcgrchri]

I have been trying to resurrect a 5970 a large pile of old instruments I have and I have been having pretty good success until I starting trying to tune. When I attempt to tune, this is what it looks like: (Please forgive the focus, it only flashes on screen for a moment and it was hard to capture)



Eventually the tune fails, because it of the changing widths. When I do a scan, if looks like this from 300 to 800:




From 10-800, it looks like this:




Maybe I am kidding myself, but below 300 AMU it looks fine.

I have cleaned the source and nothing really changed. One things I am curious about is the PFTBA. If it possible that I have a "bad" batch, with a lot of varying molecular weight material. I am skeptical about that, but this has really stumped me.

Any ideas? Any suggested relatively high MW, volatile enough materials (300+) that I might try to rule out the PFTBA?

[carlo.annaratone]

I have no idea about what's going on, but for sure you can take better pictures doing a manual tune!

[James_Ball]

Normally when you get "grass" like that in the scan, it is a quad related problem. Easy fix problem is just dirty quads, tougher fix is if it is in the mass filter electronics.

If it has been sitting a long time and not under vacuum it could simply be some contaminates have gotten into the ceramics and are still cooking out.

You can clean the quads, they are fairly easy to remove from the analyzer by removing the source then taking the long circuit boards off the side of the analyzer, then the quads just lift out. DO NOT however remove the rods from the ceramic holders, clean them as a complete unit. Also take a pencil and mark lightly on the ceramic to indicate the orientation of the quads in the analyzer so you can put them back in the same way they were.

These are the same quads as were in the 5995/5996 and I used to have to clean them quite often when we would lose power and the huge oil diffusion pumps would backstream on them. Soft test tube brush and methanol or hexane will remove most things that can get on them. Or use large Kemwipes soaked in methanol or hexane and wrap around the rods and so a "shoe shine" rub pulling it back and forth to clean the inside of the rods. Let the solvent dry overnight then put them back in and let it pump vacuum over night to remove the last of the solvent that is trapped in the ceramics.

They are very resilient, there was someone that worked on them here before me who actually cleaned a set with a brush, water and Lava soap lol. Somehow they still worked, but I would not recommend trying that.

The rods were very precisely installed into the ceramic holders at the factory, and if you remove them it is very difficult to get them back to the proper orientation.

A check you can do to see if it could be the electronics is to put it into repeating profile mode and watch the peak width for 69, 131 and 219, if they drift after letting it run for a couple hours then it could be a bad board somewhere.

The other thing to check is the adjustment of the quad drivers where you "DIP the coils". It is listed in the software as "Set RFPA" in the Execute menu I believe, and it is somewhat self explanatory, you just adjust the two adjustment screws that stick out of the end of the analyzer until you achieve the lowest mv reading at each m/z starting at 100 working up to the max in about 100 to 150 mass unit increments. Calvalve can be closed for this test as it is measuring feedback in the circuit and not a peak.

[dhdh]

Have you tried "Reset to default"? It's somewhere under the Tune menus.

[James_Ball]

Have you tried "Reset to default"? It's somewhere under the Tune menus.

Yea, try that first. Sometimes I forget the simplest of things.