Our INOVA 600 (VNMRj 2.1B) seems to have developed a problem with the lock system. The output of the lock, as displayed on the lock meter or on the lock display, seems to have a strong negative bias. The initial portion of the lock display, the part at the left before the lock "fid" actually starts, is right at the very bottom of the lock display window. I seem to recall that it used to be half-way up the window. We can overcome the bias and can still lock the system if we crank up the lock power and gain. This is OK for strong lock solvents like D2O or even 90/10 H2O/D2O. However with CDCl3 or 5% D2O the lock is very noisy and starts to saturate. Agilent TAC has suggested replacing the lock pre-amp, but my suspicion is that the lock transceiver board is more likely the problem. The questions I have for the group are:
1. Has anyone else seen a problem like this? And what was the fix?
2. Where is the beginning of the lock display trace on an INOVA? I seem to recall it being halfway up, Agilent seems to think that at the bottom is O.K. (maybe changed in DDR/DDR2 systems?)
3. On the lock transmitter side, I have at J227 (lock transceiver) 2V P-P, with 700 mV P-P at the output of the lock pre-amp, and 520 mV P-P at the probe (after the lock diplexer). These values are the with lock power set at maximum. Are these values normal? The 9 dB loss through the lock pre-amp seems a tad high, but I don't have a schematic of this module to see how they are injecting the lock transmitter signal. The lock pulse width is 35 us.
Thanks in advance!
Kirk
Kirk Marat, Ph. D. NMR Facility Manager
Dept. of Chemistry, University of Manitoba
Winnipeg, Manitoba
R3T 2N2, Canada
Ph: (204) 474-6259 FAX: (204) 474-7608
Received on Fri Aug 10 2012 - 07:16:51 MST