1101. Intermittent gain and/or phase problem.

1. Check to see if the problem happens for one nucleus or for all nuclei.

    

2. Perform a pw90, ten90, and gain test on the problem nucleus using a short T1 sample.

    

   • If the pw90 test shows arcing, reduce the tpwr until pw90 looks normal, then use the same tpwr to rerun the experiment with the problem.

      

   • If the ten90 test shows amplitude instability, check or replace the appropriate transmitter and rerun the experiment. If this does not fix the problem, check or replace the PTS synthesizer.

      

   • If the gain test exhibits gain non-linearity, check or replace the observe receiver and rerun the test.

      

   • If the problem still exists, contact your local Field Service Engineer.

1102. Image or center peak on the spectrum.

• INOVA and UNITYplus systems
  • If there is a center peak problem:
    1. Terminate the receiver input, J249, with a 50-ohm terminator.
    2. Set seqfil='s2pulq' nt=1e5 d1=2 gain=30 sw=5e3 pw=0 np=16000 in='n' spin='n' bs=1 wbs='noise'. Acquire the experiment with au.
    3. Observe the DC Offset on both channel A and B, then make the appropriate adjustment on R18 or R22 to reduce the offset to less than 10.
  • If there is an image problem:
    1. Disconnect the cable from P2X4 of CH1 and connect it to J249 on the receiver through a 40-dB attenuator pad.
    2. Set seqfil='s2pulq' sfrq=.001 sw=1e4 d1=2 pw=0 gain=30 in='n' spin='n' bs=1 np=2000 nt=1e5 wbs='quadtt'. Acquire the experiment with au.
    3. Observe the amplitude unbalance, then make the appropriate adjustment on R32 to reduce the percentage to 0. An extender board may be necessary.
    4. After the adjustments are finished, connect the cables back to original configuration and retrieve the previous parameters.
• UNITY and VXR systems
  • If there is a center peak problem:
    1. Terminate the receiver input, J2602, with a 50-ohm terminator.
    2. Set seqfil='s2pulq' nt=1e5 d1=2 gain=30 sw=5e3 pw=0 np=16000 in='n' spin='n' bs=1 wbs='noise'. Acquire the experiment with au.
    3. Observe the DC Offset on both channel A and B, then make the appropriate adjustment on R102 or R113 to reduce the offset to less than 10.
  • If there is an image problem:
    1. Extend the cable from P3406 of the Broadband Transmitter board and connect it to J2602 of the receiver through a 40-dB attenuator pad.
    2. Setup seqfil='s2pulq' sfrq=.001 sw=1e4 d1=2 pw=0 gain=30 in='n' spin='n' bs=1 np=2000 nt=1e5 wbs='quadtt'. Acquire the experiment with au.
    3. Observe the amplitude unbalance, then make the appropriate adjustment on R117 to reduce the percentage to 0. An extender board may be necessary.
    4. After the adjustments are finished, connect the cable back to original configuration and retrieve the previous parameters.
• MERCURY systems
  • If there is a center peak problem:
    1. Terminate the receiver input, J54, with a 50-ohm terminator through a blocking capacitor.
    2. Set seqfil='s2pul' tn='H1' d1=2 gain=20 sw=5e3 pw=0 np=16000 in='n' spin='n' array('nt' 1000,1,0) wnt='noise'. Acquire the experiment with au.
    3. Observe the DC Offset on both channel A and B, then make the appropriate adjustment on RV3 or RV4 to reduce the offset to less than 10.
  • If there is an image problem:
    1. Insert a rf signal with -50dBm @ sfrq frequency into J54 of receiver through a blocking capacitor.
    2. Set seqfil='s2pul' tn='H1' sw=1e4 d1=2 pw=0 gain=20 in='n' spin='n' bs=1 np=2000 nt=1 wexp='quadtt'. Acquire the experiment with au.
    3. Repeat acquiring and observing the amplitude unbalance, make the appropriate adjustment on RV2 to reduce the percentage to 0.
    4. After the adjustments are finished connect the cable back to original configuration and retrieve the previous parameters.
• GEMINI 2000, GEMINI systems
  • If there is a center peak problem:
    1. Terminate the receiver input, J2806, with a 50-ohm terminator through a blocking capacitor.
    2. Set seqfil='s2pul' tn='H1' d1=2 gain=20 sw=5e3 pw=0 np=16000 in='n' spin='n' array('nt',1000,1,0) wnt='noise'. Acquire the experiment with au.
    3. Observe the DC Offset on both channel A and B, then make the appropriate adjustment on R59 or R70 to reduce the offset to less than 10. An extender board may be necessary.
  • If there is an image problem:
    1. Insert a rf signal with -50 dBm at the sfrq frequency into J2806 of receiver through a blocking capacitor.
    2. Set seqfil='s2pul' tn='H1' sw=1e4 d1=2 pw=0 gain=20 in='n' spin='n' bs=1 np=2000 nt=1 wexp='quadtt'. Acquire the experiment with au.
    3. Repeat acquiring and observing the amplitude unbalance, then make the appropriate adjustment on R58 to reduce the percentage to 0.
    4. After the adjustments are finished connect the cable back to original configuration and retrieve the previous parameters.

1103. Consistent spikes in spectrum.

1. Attach a 50-ohm terminator to the probe observe connection, set pw=0, and take an acquisition. If the spikes disappear, the problem is in the transmitter section or probe.

    

2. Remove the terminator and connect the cable to the probe, leave pw=0, and take an acquisition. If the spikes appear, this may be a probe problem or perhaps the probe is picking up some external signal. If the spikes disappear, the problem is in the transmitter section.

    

3. If the spikes still appear, the problem is in the receiver section, see faq1017.

1104. Cannot tune probe.

1. Put the system into probe tune mode and monitor the tune meter with the attenuation switch set to the most sensitive mode.

    

2. If the meter has no reading, this indicates that there is no output from the transmitter or that the signal is lost within the path to the magnet leg.

    

3. If the meter has some reading but is not pegged, the output of the transmitter may be low.

    

4. If the meter is pegged, the transmitter is functional. Follow the probe manual to tune the probe.

    

5. If the meter has a little reading movement, retune the probe very slowly.

    

6. If the meter has no movement at all:
   • Check the output signal using a frequency counter to see if the output signal is the same as the set frequency (spcfrq). If the frequency is wrong or way off, the transmitter or PTS may be bad.

      

   • Tune with another probe or another frequency band on the same probe. If the probe is tunable now, this indicates that the probe is defective.

      

   • If the probe is not tunable, this indicates that the tune coupler or the mixer may be defective.

   To check transmitter output level, see faq1017.

1105. Noisy baseline (NMR signal is present).

1. Check using another nuclei and make sure that the observe gain is set to a normal value.
   • 40 for INOVA, UNITYplus, UNITY, VXR and XL
   • 22 for MERCURY and GEMINI).

    

2. Run pw90 test and see if pw90 is flipping normally.

    

3. If the NMR signal for all of the test nuclei is noisy and pw90 flip is normal, this indicates that the observe preamp and/or observe receiver are defective.

    

4. If the NMR signal is noisy and the pw90 flip is long, the transmitter is probably defective.

1106. NMR signal or z0 changes daily.

1. If the signal or z0 is changing downward, this may be the natural drifting of the magnet; however, if the rate of drift is abnormal, you need to monitor the magnet for possible repair.

    

2. If the signal or z0 changes upward and downward randomly, check the shimming circuitry hardware.

    

   • INOVA and UNITYplus systems:

     Check Reference Generator and z0/z1 Shim/DAC Driver boards.

      

   • GEMINI, UNITY, VXR and XL systems:

     Check Master Clock and Shim & Offset Controller boards.

      

   • MERCURY systems:

     Check Reference Generator and Shim/DAC Driver boards.

1107. WALTZ birdies when doing WALTZ decoupling.

1. Verify that the filters are installed inline with the cable to the probe. Use the highpass filter with DEC/Proton channel and the lowpass filter with the OBS/BB channel.

    

2. Verify that the probe is tuned in both BB and DEC channels.

    

3. Confirm that the dpwr value is normal by comparing it with the Acceptance Test procedures values.

    

4. Change the decoupler output to CW mode and verify that the signal is clean.

    

5. If the above steps are normal, check the probe isolation.

1108. Observing the NMR signal from a second channel

• INOVA and UNITYplus systems

  Set the observe channel using the rfchannel parameter.

  For example, for a 3-channel system, create rfchannel and change to rfchannel='213', where the first number represents the observe channel.

• UNITY and VXR systems

  Set the second channel with pulse sequence D2PUL.

• GEMINI and MERCURY systems

  The observe channel is dedicated and depends on the value of tn.

1109. Cannot do deuterium decoupling. (UNITYplus and INOVA only)

1. Make sure that the cables are connected correctly.

    

2. Verify that the amplifier is in pulse mode.

    

3. Compare the lock signal with the lock diplexer installed to the lock signal with no lock diplexer installed.
   • If the lock signal gain through a lock diplexer drop is significant, the lock diplexer module is defective.

      

   • If the lock signal is normal, check the output of the amplifier.

For a detailed troubleshooting guide, check the chapter on the Lock/Decoupling Accessory in the UNITY Accessory Installation manual.

1110. Spectrum does not decouple with WALTZ (XL,VXR, UNITY only).

1. Does spectrometer decouple in CW mode?

    

   • If it doesn't decouple, the decoupler transmitter may be defective.

      

   • If it does decouple, check the modulation mode on the Digital Interface board and see if mode A and B are switching when the decoupling mode (dmm) is changed.

    

2. If WALTZ mode cannot be selected, the digital section may be defective. Check or replace the Output board and/or Acquisition Control board.

    

3. If the WALTZ mode can be selected, check or replace the Master Clock board and/or the Offset Synthesizer board.