Dear Ferron! there are several thougts, as the reasons can be different: bad sample, improper VT conditions (unstable temperature, incrorrect gas flow), Topshim miscalibration or even dirty or cracked insert glass.

1. Set normal temperature (298-303K, 400-550 l/h gas flow, run VT selftune)
2. try with standard sample (1% CHCl3 in Acetone) or even run Topshim 3D with 2mM sucrose sample. If final B0 Std.dev (after 3D) is below 0.5..0.8 Hz Hz your probe is most probably OK
3. check sample position in spinner and solvent height - are them ok? Maybe, in contrary, too much solvent and experiment is on elevated temperature?

4. Try extra parameter convcomp (convection compensation). Works under stable VT conditions (also check.

5. The last, but not least: sample homogeniety. Solid particles, high viscosity, aggregation?

Dear Ferron,

please provide the topspin version, you can start trying with "topshim gui" select 3d shim and use 10% d2o and 90% h2o sample, after finishing save this shim.

now put line shape and then try the "topshim" only. if you see the improvement then do a little bit manual shimming of z, z2, z3. depends your spectra -how it's shape showing.

Other wise try with - lineshape and take hump optimization in "topshim gui" command.

It should work very fine..otherwise need some checks- Hardware; 2H pulse length; 2H amplifier; Gradient; Probe coil cleaning; Probe insert cleaning.

hope this will help you.

Man Mohan

Two suggestions: 1) In the "Service" tab of the Topshim panel, there's a "calibrate" feature that you can use to get the system talking to the probe more effectively. Last year, we sent a probe out for service and when it came back we had a terrible time shimming it with Topshim. Once an engineer who happened to be onsite pointed out this button, we clicked it and let the software do its thing and we were then able to Topshim very effectively.

2) If you're primarily running organic samples, I've found we get better 3D shims by using an ASTM standard (40% dioxane in benzene-d6) and using the command "topshim astm 3D". We do this as part of our weekly maintenance with a doped ASTM standard, which also affords us easy access to quickly calibrating carbon 90-degree pw's.

Not to bring up a dead topic, but I've been having this issue as well. Here's what I did to solve it.

First make sure topshim is using the correct solvent by running 'lock' from the topspin command line (silly, but this took 2 hrs for me to figure out).

If the shims are really off, topshim can find a 'local maximum' in the local signal that gives terrible line-shape. For instance, you shim by hand (save shim file!) for a good line-shape, then run topshim, the lock-signal comes up, but the line-shape is terrible.

The solution, is to 'walk' Z and Z2 by hand. Start with your reasonable line-shape, and change one, yes, the line-shape will get worse, but now change the other until the line-shape gets better again. (Save your shim file again!) Now re-run topshim. If it works, you're done. If it doesn't, load that shim file and walk the peak with Z & Z2 a bit more. Repeat wsh and topshim again until it starts giving good results. While walking you should be able to use the lock level to guide you if you are going in the right direction (although you too may find the fake local max this way).

A few other things I noticed, take these with a grain of salt. Running topshim using the 'lineshape hump' optimization seems to be less susceptible to finding local maxima with poor lineshape. Also, checking z6 in topshim seemed to help.

I hope this helps anyone else having this problem.

It is good to see so many possible answers. I think that it shows that there can be many reasons for this. Topshim is a complex beast and there are many options that can help. Often if doesn't do well if the non-spinning shims are wrong and it tries to compensate for this with the Z shims. If you are seeing this on all samples, performing a 3D shim on D2O/H2O is a very good start.

If you have been performing VT experiments, it can take a long time for the shims to get back to normal. You could try a topspim tunebxyz which will attempt to fix the off-axis shims before doing a topshim on the Zs. Sometimes it tries to fix things with the higher-order Zs, in which case you can limit the order to Z3 by adding the option "ordmax=3".

In general, I find topshim performs brilliantly. It only tends to fail if there is a system problem (broken glass insert for example or warm RT shims) or if the off-axis shims are out...

One last thing to check is that none of your shims has a high current in it. This can cause heating and instability in the RT stack.

I hope something in this helps!