Dear Colleagues,
I have a very vexing problem with a Bruker 600 DRX console.
The console is configured as a standard four channel console
for biomolecular NMR experiments. The console has been in
service for ~8 years now.
The first problem I noticed was that while the hard 15N 90 deg
pulse was behaving normally, the 15N 90 deg pulse used for
decoupling appeared to be a lot longer than what it had been,
i.e. the power level needed to achieve a 90 deg pulse was a lot
higher (by several dB) than what we had been using.
On this console the "f3 channel" is designated as the 15N channel.
I began to trace the signals on the f3 channel upstream of the 15N
BLAX300RS amplifier. I have repeatedly found that the output of the
ROUTER
is almost TWICE as LARGE as the output of the ASU which of course is
upstream.
One would normally expect, if anything, a slight degree of attenuation
of
the signal going through the router. However, I observe a significant
increase of the signal intensity coming out of the ROUTER compared to
the signal coming in from the ASU board. As I stated I
When I look at the f2 and f4 channels I get the result one expects: the
signal out of the ROUTER is basically the same amplitude of the signal
going into the ROUTER.
I do not know how but I believe this odd behavior is causing the
problem I observe
with the much longer 15N decoupling pulse. I used the the f2 channel to
fire the f3 channel by swapping the cables going into the preamp.
When I do this I get the expected behavior for 15N pulses, i.e. the
hard pulse
duration and power level is typical and the decoupling pulse is of the
proper
duration at a power level one would expect. So this would seems to
rule-out
any funny business going on with either the 15N preamp slice or the
probe.
I have done additional extensive troubleshooting including swapping the
ROUTER,
ASU and FCU boards (using identical boards in our console), swapping
the control
cable from the FCU to the ASU, installing a new TCU board and trying an
identical
but different amp and I still see the same problem, i.e. a larger
amplitude signal out of
the ROUTER compared to the signal out of the ASU and much longer
decoupling pulse.
Even with the the FCU, ASU and ROTUER boards and the control cables
swapped the
f2 and f4 channels behave normally.
I apologize for the excessive length of this message. But I am hoping
someone
may have observed this problem previously and can share the fix.
Thanks in advance,
Ben Ramirez
Received on Fri Jun 06 2008 - 05:47:52 MST