Service – American Magnetics 420 Power Supply Programmer User Manual
Page 119
101
Service
Troubleshooting Hints
an open switch heater connection.
The displayed voltage divided by the switch heater current should
be approximately equal to the persistent switch heater resistance.
If this is not the case, check the continuity between the persistent
switch heater power supply output pins on J7A or J7B and the
connector on the magnet support stand top plate. Refer to Table A-
1 on page 105.
2. Verify that the output of the persistent switch heater power supply
is set to the appropriate value. Refer to paragraphs 3.2.2.5 and
Figure 3-5 on page 50.
3. Ensure that there is sufficient time for the switch to warm before
the power supply current is changed.
5.2.11 The magnet quenches for no apparent reason.
1. Ensure the magnet is not being charged at a
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exceeding the capabilities of the magnet. Exceeding the designed
rate for ramping the magnet may cause a quench or it may turn on
protective diodes on the magnet which may appear very similar to a
quench.
2. Ensure there is adequate LHe level in the cryostat. For systems
operating at less then 4.2K, ensure the magnet is cooled to the
temperature specified by the magnet manufacturer.
3. Disable the Model 420 quench detection feature (see paragraph
3.5.1 on page 62) if you suspect the Model 420 is falsely indicating a
quench condition.
5.2.12 The Model 420 will not lower the field in the magnet.
1. Ensure the magnet is not in the persistent mode. Refer to
paragraph 3.4.2 on page 60 for the procedure to remove a magnet
from the persistent mode of operation.
2. With the persistent switch heater on, press the 1 key in the default
display to show the switch heater voltage. A value of 0 V indicates a
shorted switch heater connection. A value exceeding 17 V indicates
an open switch heater connection.
The displayed voltage divided by the switch heater current should
be approximately equal to the persistent switch heater resistance.
If this is not the case, check the continuity between the persistent
switch heater power supply output pins on J7A or J7B and the
connector on the magnet support stand top plate. Refer to Table A-
1 on page 105.