Date: Fri, 22 May 2015 18:31:28 +0000
Dear AMMRLers,
I feel so fortunate to be part of AMMRL, such a rich resource for information and an unbelievable group of NMR wizards who I can turn to reliably when desperate or not.
Good News:
The problem was resolved yesterday!
Acknowledgements:
I am grateful to all of you who have responded to my inquiry (see below): (listed here in the order responded. Please forgive me if I've missed anybody here)
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David VanderVelde, CD Rithner, Moni M S, Richard K. Shoemaker, Jerry Dallas, Gregory J. Heffron, Weiguo Hu, Arnold Itkin, G-Sukenick, Clemens Anklin, Sandip Sur, Alan Kenwright,
Marcus Wright, Shaoxiong Wu, Zhe Zhou, Bill Kearney, Feng Rui, David Grace, Simon Barrett, Don Eldred, Tim Claridge, George Furst, Pierre Audet, Ryan McKay, Donald Fulton, Karl Koshlap, Jerry Hirschinger, Brian Breczinski, Rolf Tschudin, Jon Webb, Neil Jacobsen, Hongjun Zhou, Weidong Hu, Bill Stevens, Junfeng Xiang, Monika Ivancic, Sameer Al-Abdul-Wahid, James Hook, Patrick Hays
Responses:
Total: 39
[cid:image004.jpg_at_01D09482.D0209540]
Tests Performed:
Once again, statistics can hardly go wrong. We went straight to the PTS for 1H and measured the DC voltages on the PS board with a multimeter and their ripples with a scope probe. One of the voltages which is supposed to be -12.4V turned out to be just -11.75V with obvious ripple modulations.
Solution:
The axial electrolytic capacitor responsible for the -12.4V DC was replaced with a new one (< $10 from a local electronics store) with the same electronic specs: 25V and 10000uF, but different physical dimensions: 26mm dia x 46mm L for new vs 22mm dia x 52mm L for original. As a result, the 120Hz spurious pickups were gone, and the 1H spectrum started looking beautiful again. We were lucky we hit the jackpot the first time, thanks to all of you.
Original Inquiry:
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Dear AMMRLers,
On our Bruker DMX 500MHz SB solution NMR instrument, each 1H signal is accompanied by spurious pickups which are 120Hz apart from each other and from the signal and have variable phases, as shown in the spectrum below for a CDCl3 solvent. Inputs as to the reasons and fixes for the pickups are very well appreciated.
[cid:image002.jpg_at_01D08989.394D8190]
Cheers,
Jerry
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Jerry Hu, Ph.D.
Technical Director Email: jghu_at_mrl.ucsb.edu<mailto:jghu_at_mrl.ucsb.edu>
Project Scientist Tel: (805)893-7914 (office)
Materials Research Lab, UCSB (805)893-7940 (lab)
Santa Barbara, CA 93106 Fax: (805)893-7914
http://www.mrl.ucsb.edu/spectroscopy-facility
attached mail follows:
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