GAB/2
H172203_1_001 93 / 234
Some of the necessary checks are described in detail below. It depends on the preceding
test results, which check actually has to be performed next. Typically, not all checks have to
be executed.
1. Run a gradient experiment
Run the parameter set gradshim1d1h (rpar gradshim1d1h) and check if the resulting profile
has the expected shape.
You can execute a Bruker standard experiment (e. g. gradient COSY) on a nucleus other
than your lock nucleus (typically 2H for lock) with activated NMR lock. You should be able to
see the deep dips in the lock level (check the lock display) while the gradient is active.
6. Check for unintended / faulty ground connection
In case of a faulty connection between one of the gradient wires and the ground potential
there is typically a current flowing. This current has an influence on the Z1-Shim and
disappears as soon as the gradient connector is unplugged. A perfect shim with the influence
of that current would get significantly worse without, and the lock level would drop
accordingly.
7. Measure gradient cable between pin 2 and 3
Unplug the gradient cable and measure at GAB/2 side. Since the resistance of the gradient
(cable and coil) is very low, the measurement has to be made very carefully (at best
differential measurement).
8. Connect an oscilloscope to the monitor output
The monitor output on the GAB/2 provides a voltage that represents the current actually
provided by the GAB/2 current source. 1 Volt represents 1 Ampère current, which is a
gradient strength of 10%. If the voltage at the monitor is only a few millivolts and very noisy,
there is probably no gradient load connected. In this case, the gradient cable and the coil
resistor have to be measured by an Ohm meter (see point 16).
9. Suspicion of open gradient load
If you suspect an open gradient load please contact your local Bruker office.
10. Use the BSMS Service Web to get the GAB/2 state
In TopSpin type ha to get access to the Service Web.
11. Restart the GAB/2 on the corresponding Service Web page.
Perform the indicated command sequence. Wait about 10 seconds before depressing the
Refresh button. If you have no success, you may try several times.
12. If there is a DPP
The GAB/2 can operate without DPP and has its own preemphasis generator. The DPP is
therefore not necessary and should be removed. Some versions of the DPP did not provide a
parity bit, which would cause communication errors.
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