Date: Fri, 9 Apr 2021 19:14:51 +0000
Hello Everyone;
I hope you and yours are well during these difficult times.
A few months ago our old Varian 400MR developed a strange, intermittent problem:
occasionally next to an authentic peak in a 1H 1d (the most common experiment run)
numerous small peaks—a kind of a sawtooth pattern—would be present (top figure
below). These could be either on the up-field or down-field side, and did not depend
on which solvent was used. Less frequently this artifact would present as a doublet.
Sometimes it basically looked like very poor shimming (bottom figure).
I believe the problem disappeared for a few months, but has just recently reappeared.
Someone said that after getting a bad spectrum they immediately re-ran it with the
lock off, as I had asked them to, and they got a normal spectrum. However, sometimes
just re-running the spectrum with the lock still on also results in a normal spectrum.
This is somewhat reminiscent of an intermittent problem we had with our Inova 500
a few years ago, which was the result of a problem with the z0 / z1 shim board. As I
recall, however, that looked more like ringing.
Thanks in advance for all of your help!
Stay well,
Karl Koshlap
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