I sent a query a while ago about pumping the vacuum space of a donated Mercury-400. We are now at field and everything works fine EXCEPT:
The deuterium lock will lock in perfectly with lockphase set to 0 or 360, but the lock signal is negative. The display goes down rather than up when it locks. The field is stable and you can do long acquisitions. If I set the lock phase to 180, it doesn't lock and the lock frequency drifts away from zero frequency.
The problem is that you can't shim on the lock signal. The shim display (red thermometer) shows zero lock level because it can't display the negative lock signal.
I've tried many combinations of rebooting the host computer, restarting the acquisitons computer, power cycling the console, etc. I considered the possibility that I'm locked on a 2H sideband, but I get a 1H spectrum centered in the spectral window normally using the standard parameters and tof=0, and I can't find any other 2H signal in the complete range of Z0 (-2048 to 2048).
I have to assume that some component in the lock system has gone bad during the long (4 year) sleep of the console, but I keep wondering (since it's a Varian) if it might be a software issue. I would appreciate any suggestions.
Neil
Received on Mon Jul 06 2015 - 06:50:16 MST