Dear AMMRLer's,
We have been troubleshooting a problem for weeks without success, on our avance II hi res 400 bbo-z spectrometer here at the UBC nmr facility. The system is running XWINNMR3.5pl6 on Linux OS.
When running gradient pulse programs (DOSY, COSY, HMQC etc) after aproximately 10 - 12 minutes, the lock hold will intermittantly start to beep on the BSMS keypad and you can see the lock signal gets lost (screen lock signal does not quickly rebound back up to normal level - instead stays down for about one second until the system increases the lock power).
When running DOSY the error message that appeared (when problem started, a few minutes into DOSY experiment) says:
'GCU error:gradient output request while timer is active
PREAMP_ramp_time,gradient_pulse or GC_Control_sequence too long?'
In the 2D grad homo and hetcor experiments. If you continue pulsing...after a similar time frame (10-12 min) the lock signal returns to the familiar blank and unblank routine...then is lost again after 10-12 min. This only occurs with grad pulse programs. The 2D data is definitely corrupted. The problem is not NS or TD dependent.
1. We have checked the lock amp boards and exchanged them with others without eliminating the problem.
Boards exchanged: LCB (Lock Control Boaard),GAB (Gradient Amplifier Boaard),L-Rx, L-Tx (Lock Receiver and Transmitter), and CCU (Computer Board)
Diagnostics performed on AQS I960 boards; TDC, GCU, FCU - all passed ok.
2. We checked the gradient pulses at the GAB monitor output while simultaneously monitoring F1 and F2 Rf output on scope...all looked normal and correct.
Timings (d0 increment) appeared to advance normally even during problematic range.
When problem occurs, GCU 'Pulse' LED is on for about 1 sec (instead of normal very brief flash), however GCU Monitor output is perfectly normal during this time.
3. We tried changing the grad blank command at the end of the pulse program...moved it from just before 'go=2' to just after it. No change in problem.
4. We tried reducing the strength of gradients to half their values in gradCOSY or gradHMQC. No change in problem.
5. It was noted that the 'Lock Hold' cable was not connected to the Lock Control Board (LCB). Connecting it did not eliminate the problem. Same occurrence of lost Lock. BSMS keypad was however not beeping now and would indicate 'Lock Hold'. Data still corrupted as before.
Has anyone had a similar problem to this and resolved it??
Thanks for any info or suggestions.
Nick
Nick Burlinson PhD
Director NMR Facility
Chemistry Dept.
Univ. British Columbia
Vancouver BC
V6T 1Z1
604-822-6787(nmr lab)
604-822-6956(office)
Received on Mon Aug 13 2007 - 11:31:54 MST