Dear John,
the best starting point should be to first locate the 1H signal of H2O
(e.g. 90:10 H2O/D2O "sucrose sample"). You should be able to see it regardless
of how bad the shim is. Start with all shims set to zero.
Set the spectral width to 1 MHz (QSIM acquisition mode instead of DQD), set
pw to 1-2 us and ns=1, lock field=0 and lock sweep off - you should normally
get a signal. Set it on-resonance with the cursor, repeat a scan and check the
new SFO1. Use this in CF and run expinstall.
Then check lock offset/field and lock phase (very possibly wrong) - with lock
sweep on, set the red/green "wiggles" on-resonance first using the field value,
then change the phase until both red & green "spikes" have the same size. Try
to switch the lock on now - you should get a straight line.
Now try to shim a bit z1, z2, X and Y, extend a bit to ZX & ZY, return to Z1/Z2/X/Y
and repeat until the lock doesn't go much higher. You may try to give topshim3d a try now...
Cheers
Bert
> Am 12.08.2026 um 16:48 schrieb John H Grimes Jr. via groups.io:
>=
> Due to a recent magnet loss we found ourselves with an extra Avance III-HD
> console, BBO probe, BST and shim stack. As “luck” would
> have it, another department with an old failing Varian had a magnet of the
> same strength. The starting magnet was an Oxford AS600 and the destination
> magnet an unshielded Oxford compact flat bottom 600. Both with 51 mm bores
> and having the centerline indicated as being the same distance from the
> bottom in their respective manuals. The distance to the top on the unshielded
> magnet differed by 9 mm so we made slight adjustments in the collar on the
> BST to account for this. We configured (cf’d) the console on its
> new magnet and entered the new field value which we had taken from the Varian
> sfrq parameter. We’re searching for a lock signal but see none.
> So I wonder if we either have the probe in the wrong place, sfrq doesn’t
> equal sfo1 or a combination of both.
>
> Can anyone recommend a systematic method for adjusting the probe height and
> searching for a lock signal?
> How far away from the sweet spot can the probe be but still show a signal?
>
> Thanks,
>
> John
>
> John Grimes | NMR Facility Manager
> Complex Carbohydrate Research Center, University of Georgia
> 315 Riverbend Road
> Athens, GA 30602-4712
> jgrimesjr_at_uga.edu
>
>
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Received on Thu Aug 13 2026 - 10:20:33 MST