Xi-an Mao,
Regarding your lock instability, I suspect the gradient amplifier/
power supply is the problem. We had the same phenomenon on our Varian
Inova a little while back.
When on, the gradient amp supplies a small current to the probe's
gradients, which then act like shims. For fun, try shimming up a
sample on a working system, then turn off the (z) gradient power. You
should find that the lock levels falls and the lineshape gets
distorted, but both can be restored by adjusting the z1 shim.
If your problem is like ours, your gradient's "off" current is
unstable, effectively mimicking an unstable shim. Thus, your gradient
amp needs service. If you're sending it in for repair, you'll need to
be in close communication with your repair engineers. I got the
impression this is a weird failure, and the amp may still pass all
their normal tests.
Good luck!
Josh Kurutz, Ph.D.
Tech. Dir., Biomolecular NMR Facility
University of Chicago
On Jul 29, 2008, at 10:09 AM, "Xi An Mao" <xmao_at_wfubmc.edu> wrote:
>
> Dear All:
>
> We have problems with our two Bruker cryoprobes. One probe does not
> response to proton tuning/matching, but the other channels (13C, 15N
> and 2H) work fine. The other probe has unstable lock level. One when
> the gradient cable is disconnected can the lock level remain calm.
>
> I am wondering if anyone of you had similar problem and how did you
> fix it. I appreciate all feedbacks.
>
> Best regards.
>
> Xi-an Mao
> Cleveland Center for Structural Biology
>
Received on Tue Aug 05 2008 - 14:36:04 MST