INOVA system Diagram:

Perform the follow procedures if you take an acquisition and your resulting spectra shows noise only.

1. Check to see if you can lock and shim your sample.  If there is no lock signal return to the section for troubleshooting the Lock Path.
2. If you have a lock signal then you should change your tn to the another band.  For example, if you took a proton acquisition and your spectrum showed noise only then change your tn='C13' or setup your standard C13 parameters and take a spectra using a sample that you know will have C13 peaks (Use the C13 sensitivity sample).  If you have lost only one band then that is usually an indication of a switching or amplifier problem.  If you do not have peaks with either nuclei procede to the next step.
3. The next step would be to measure your transmitter pulses at the probe input.  Depending on what frequency system that you have will determine what point to measure.  For this explanation we will just use general test points.  Assuming that you have no spectra for either band we will setup to pulse the probe and measure at the proton input to the probe.  Setup your parameters using the following:
at=.1
pw=50
bs='n'
dm='n'
nt=1e6
tn='H1'
tpwr=63
Connect a cable through a 30db attenuator from your o-scope to the probe output of your preamp.  start the acquisition by type go from the VNMR command line (if you have switching relays in your magnet leg you will want to check for pulses at the cable that connects directly to your probe).
Set your o-scope time base so that you can view a 50 usec pulse.  the amplitude of these pulses should be approx.  2.5 to 5 V P-P.   If there are no pulses at the probe you can assume that your problem is in the transmitter path, procede to that section.  If there are pulses at the probe, check to ensure that you are pulsing at the correct frequency.  If the frequency is correct then you should test your receive path using signal injection.  Procede to that section
Check the power supply DC voltages.  It is possible that one of the voltages is low or missing.

Measurement Points and Signal Levels For Troubleshooting the Transmitter Path

If there is no transmitter signal at the probe, you will need to start to follow the signal back or bracket the path to divide the transmit path even further..   All signal levels are based on the transmitter power set to maximum (tpwr=63).
Transmitter Path Measurement Points
Transmitter #1  (these signals are measured straight into the o-scope)
J2X4 Synth Input   +10 dBm
J2X5 LO Output   +10 dBm
J2X3  Xmittr Output     +10 dBm
N Channel Attenuator
J297 Channel A Output  approx. +4 dBm
J298 Channel B Output  approx.  +4 dBm
AMT #1
J4073  Channel A Output  +12 - +17 dBm  (measured through a 30 dB attenuator)
J4072  Channel B Output  +24 - + 26 dBm  ( measured through a 30 dB attenuator)
You should see approximately 50-55 dB of gain across the AMT amplifier.  To verify this gain you must measure both the input and output at the AMT amplifier
Receive Portion of the Lock Path
You can test the receive portion  by injecting a signal at probe input of the preamp.  The injected signal must be at -75dBm and should be at your transmitter frequency.  You can use a signal generator to inject the signal or you can also use your Transmitter #2 output (if you have a dual brodband system).    Once you have injected the signal, take an acquisition, you should observe a peak in your spectra.

Setting up Transmitter#2 for signal injection.
Make the follow changes to your experiment setup