We recently powered down our INOVA 600, (VNMRj 2.1B, 28 channel shims) in order to change out the VT cable (another story - another time). I know it probably wasn't necessary to power down the whole console to change this cable, but it is a tight space and didn't want to chance knocking out some of the other ribbon cables etc. in a live console while struggling with the VT cables. On powering the system back up, we can no longer load any shim files. rts('shimfile') leaves all of the shim settings in the shim panel at zero. Clicking the buttons with the mouse you can change the shim values, but svs('temp') with these new values followed by rts('temp') returns all of the shims to zero. Examining the shim files with an editor confirms that the file contains reals shim numbers and not zeros!
Upon looking at a proton signal (2% H2O in 98% D2O) it would appear that no shim current is going to the magnet. The peak is about 45 Hz wide. Attempts to adjust the shims with the shim panel buttons in VNMRj results in no changes in the spectrum, even when moving Z, X, or Y over their full range. I know that at least part of the analogue part of the shim system (Z0) must be working because if the lock is activated with no lock signal (lock cable not connected at probe) the peak will drift as the lock system accumulates an error signal. However, adjusting Z0 with the software leaves the peak unchanged.
My dilemma is, is this likely a problem with the shim power supply? Or a failure of the MSR board to communicate with the shim supply?
Anyone seen anything like this before? Any suggestions for troubleshooting?
Thanks!
Kirk
Kirk Marat, Ph. D. NMR Facility Manager
Dept. of Chemistry, University of Manitoba
Winnipeg, Manitoba
R3T 2N2, Canada
Ph: (204) 474-6259 FAX: (204) 474-7608
Received on Thu Oct 25 2012 - 16:28:14 MST