Well! This can happen because of two reasons.
1. Your probe position has changed...if it is not tight enough, because of
air pressure and freuqent insert and eject cycle the probe goes down and
hence lock is poor, shim is poor and signal to noise is poor. Check the
probe position in the magnet.
2. Alternately, the level of cryogen (Liq. Helium) may be two low and
requires urgent fill.
There may be a third possibility of shim power supply capacitors
going bad and giving poor voltage in the shim board or the supply of shim
DAC may be bad.
Best Luck. Happy shimming!
L.S.Mombasawala.
NMR Lab, IIT, Bombay.
__________________________________________________________________
On Fri, 1 Apr 2005, Edward E. Waali wrote:
> NMR Folks,
>
> After powering up our Unity Plus 400, Z0 is in a drastically new
> position for a given solvent. What's more, after locking, good homogeneity
> has been impossible to achieve so far. It's truly horrible.
>
> Has anyone seen this before? Thanks!
>
> Ed Waali
>
> ******************************************************************
> Edward E. Waali
> Department of Chemistry
> University of Montana
> Missoula, MT 59812
>
> Voice: (406) 243-4992
> FAX: (406) 243-4227
> E-mail: edward.waali_at_umontana.edu
>
> ******************************************************************
>
>
Received on Mon Apr 04 2005 - 08:54:17 MST