Quick question - do you really do triple -resonance on that machine?
If not, you can just route the control cable and input/output from fcu2 that normally goes to the "middle channel" on the Schomondel to the "bottom channel". I limped along like this for years as we had other systems to do triple-resonance.
If you order a replacement, don't bet that it won't come with a new problem as these things are old and in short supply...
-----Original Message-----
From: Jacobsen, Neil E - (neil) [mailto:neil_at_email.arizona.edu]
Sent: Monday, February 09, 2015 3:05 PM
To: ammrl_at_ammrl.org
Cc: Bao, Kevin - (kbao)
Subject: AMMRL: Defective channel in Schomandel frequency synthesizer
Our DRX-600 has a three-channel Schomandel, and there is a problem with channel 2. It works fine for 13C (HSQC, HMBC, etc.) but not for 1H (1H dec. 13C, DEPT). The output is about 50 mV P-P for 1H, 1.6 V for 13C. In the 1H wobb display, we can see a normal response below 600 MHz, but crossing over the 600 MHz line drops the response by a factor of 10. If we swap the F1 and F2 channels in the Schomandel (by switching the inputs and outputs), the 13C observe works with good 1H decoupling, but we get very weak 1H signals on a 1H spectrum. So clearly the problem is the second channel of the Schomandel.
Bruker has a replacement in Germany, but it costs $13,000! We have taken the Schomandel apart and we're trying to figure it out. I have a few questions:
1. How does the 3-4 MHz signal combine with the analog signal from the synthesizer? For example, is it subtracted: 604 MHz (analog) - 3.87 MHz (DDS) = 600.13 MHz? If that is the case, the problem arises in switching from 603 to 604 MHz in the Schomandel.
2. How does the synthesizer put together the analog signal? We see 10 parallel modules, each with two crystals. Does that mean one is 100/200/300...900 MHz and the next is 10/20/30/...90 MHz, and so on down to 0.1/0.2/0.3...0.9 Hz? I'm hoping that we simply have a bad output transistor in one of the modules.
3. Does anyone have schematics for this NDT-1000 synthesizer?
4. Is there a significantly cheaper source of repair or exchange for a Schomandel?
Thanks!
Neil
Neil E. Jacobsen, Ph.D.
NMR Facility Manager
Department of Chemistry and Biochemistry University of Arizona
1306 E University Blvd.
Tucson, AZ 85721
520-621-8146
Received on Tue Feb 10 2015 - 10:02:36 MST