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CHAPTER 6:
Maintenance and Troubleshooting
Model CRX-6.5K Probe Station
6.3.2 CCR
Troubleshooting
For troubleshooting, refer to the HC-4E1 Helium Compressor Technical Manual and
the Cold Head Models CH-202, CH-204S, CH-208R and CH-208L Operating Manual.
6.3.3 Probe Station
Cooling
Troubleshooting
Many probe station cooling issues are actually symptoms of vacuum problems. It is
advisable to review section 6.3.1 before proceeding with this section. The most
common sample cooling assembly cooling problems are listed below.
6.3.3.1 Probe Station Does Not Begin to Cool
Use this section if the Model CRX-6.5K stages do not begin to cool. The first step is to
make sure that all temperature controller heater loops are turned off or have a 0 K
setpoint. If this has been verified, then the problem is more likely a problem with the
CCR:
D
Ensure that the CCR compressor is on and operating properly
D
Ensure that the cold head electrical cable is connected to both the compressor
and the cold head
D
If the CCR compressor is operating but the cold head is not cooling the probe
station, stop operation and contact Lake Shore
6.3.3.2 Sample Stage Will Not Cool
If the radiation shield stage cools but the sample stage does not, verify that the
sample stage temperature control output is off.
If the sample stage temperature control is off, then your problem may be a result of a
malfunction with the CCR cold head second stage. Stop operation and contact
Lake Shore.
6.3.3.3 Radiation Shield Stage Will Not Cool
If the sample stage cools but the radiation shield stage does not, verify that the
radiation shield stage temperature control output is off. If the radiation shield stage
temperature control is off, then your problem may be a result of a malfunction with
the CCR cold head first stage. Stop operation and contact Lake Shore.
6.3.3.4 Sample Stage Does Not Reach Base Temperature
The Model CRX-6.5K sample stage should be able to cool to within 1 K of base
temperature in approximately 2 h. A large number of problems can prevent the
sample stage from reaching base temperature, because every subsystem needs to be
optimized simultaneously. Common problems are:
D
Poor vacuum
D
Probe arm position: placing probe arms in the fully retracted x-axis position
presents a greater heat load to the sample stage, as more of the arm’s length will
be outside of the radiation shielding; extend the probe arms into the probing
area to reduce the heat load to achieve base temperature
D
Extra heat load on the sample stage: can be caused by arm braids touching
improperly, temperature control heater left on, microscope light left on, or all
probe arms positioned all the way out in the x-axis
D
Improper temperature controller setup: if the temperature controller inputs are
reconfigured, it is common for the wrong temperature response curve to be
selected for a sensor
D
Repeated thermal cycling of the sample stage without warming the system to
room temperature will degrade base temperature operation. This is a common
behavior of cryocoolers. Each time the sample stage is warmed above
approximately 100 K and returned to base temperature, the base temperature
will be slightly higher than what was achieved during initial cool down. Warm
the entire probe station to room temperature (section 4.5.4) and cool again
(section 4.5.2) to reestablish specified base temperature.
