Here's a brief summary of the responses I got to my query about PFG coil failures. Thanks to all those who replied – I believe I thanked most if not all of you individually.
Although it's not all that common of a problem, the long and short of it is that PFG coils can and do fail due to mechanical stresses. Most of the probes it's been seen in are older, and the "average" age at which probes develop a problem seems to be over 10 years. Often it's a loose or broken connection of some sort, although the coil itself can become damaged. Typically the repair is replacement of the gradient coil in the probe, although sometimes one can resolder a bad connection. Using shaped gradients may cut down on wear and tear and prolong the life of your gradient coil.
In my case, the problem actually turned out to be a broken solder connection for the Z gradient wires in the upper barrel, which had about a 1 mm gap between the 2 wires once I cut off the heat shrink. I was focusing on the probe since the gradients behaved normally on our BB probe but didn't work on the HCN probe, possibly due to differences in how the pins mate with the upper barrel. Those of you with older style Varian PFG probes may wish to include a visual inspection of the upper barrel in your initial troubleshooting.
Cheers,
Andrew
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C. Andrew Fowler, Ph.D. | University of Iowa
Associate Director | B291 CBRB, 500 Newton Rd.
CCOM NMR Facility | Iowa City, IA 52242
319-384-2937 (office) | 319-335-7273 (fax)
andrew-fowler_at_uiowa.edu
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Received on Tue Nov 27 2012 - 08:02:19 MST