Have you ever colleccted NMR data and found that the signal-to-noise ratio was very poor even though you just KNOW that there is absolutely nothing wrong with your sample? If so, the following note may help you figure out the problem. The flow chart in the note is especially helpful.
Daniel D. Traficante, "Elementary Trouble-Shooting for Poor Sinal-to-Noise Ratios of NMR Spectrometers" Concepts in Magnetic Resonance, 2, 63 (1990).
I must admit that when students come to me with poor signal-to-noise ratio problems, the first thing I check is the sample. Most often this is the problem as many people really have no idea how much sample they have in their tube or the sample is cloudy or has precipiate or is not filled properly or is paramagnetic or is a complex mixture......... If the sample appears OK, I use the logic in the note above to help isolate the problem.