Re: [AMMRL] Overcurrent SCB20 Shim Board #Bruker #Hardware #Troubleshooting

From: Michael Groves <m.groves_at_utah.edu>
Date: Thu, 6 Jul 2023 15:49:09 +0000

Hi Adil,

Usually when I've seen shim board errors, it turns out to be something
associated with the shim system and it's not just a weird error.

There are a couple of things you could look at: If you swap the shim boards
(with the system powered off) does the error follow the board or is it
consistently on SCB20(2)? If it follows the board then you have a good
argument for replacing the board. If it doesn't, maybe check the rest of
the shim system. I have seen (rarely) shim coils open up in the shim coil
itself and this can cause shim system errors. If you think the error is
in the shim coil, attached is a document with the expected resistances for
the various shim systems - yours is a BOSS-3 and if you've got a multimeter
you can easily check the resistances.

There is another possibility - you might just have a pathological set
of shim currents that are causing high shim currents in SCB20(2). Look at
the y (yz, yz2 ...), the xy (xyz ...) and the (x^2-y^2 (and so on) shims and
see if any of the shim currents is particularly high. You could also just
go into the BSMS service webpage and look at the currents supplied by each
board to see if any of the current measurements looks too high.

There is one other thing you might try just in case - sometimes a spurious
current gets set that isn't part of any one shim so when you change shims it
ends up causing strange behaviors. If you want to check this, I would first
save the shim values, or write them down - get them somewhere that you can
refer to them. Then go into the BSMS shim page and there's a button that will
let you set all shim currents to 0. Do this. Then go back to topspin. Use
the"wsh" command to save the file with all shims zeroed. Then manually set
the shim values to what they were before. Don't read in the shim file - that
will bring back whatever spurious currents might have been there. Setting
the shims manually will ensure that the only currents applied are the ones
that you want. After that, save that shim file.

These are the things I would try, in order from what I think is most likely
to least likely. But still possible.

Cheers,
Mike

[Block U Logo]
Michael Groves (he/him/his)
NMR Operations Manager, D.M. Grant NMR Center
Department of Chemistry
The University of Utah
315 South 1400 East, GH Rm 1487 Salt Lake City, UT 84112
o:801-581-3828
c:385-910-9856





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Received on Thu Jul 06 2023 - 08:53:38 MST