connecting the connector and checking the probe resistance. This can be
done in place without disturbing the physical adjustment of the probe.
The following procedure is recommended for testing and/or replacing
the sample probe:
1. Place an empty sample tube in the freezing chamber (Figure 5, Item
8) to catch any extraneous material that might fall in.
2. Unplug the instrument, it is not sufficient to just turn it off.
3. Remove the head cover by removing the two top screws and pulling
the cover straight up.
4. Unplug the sample probe connector (Figure 10, Item 1). The probe
leads are electrically accessible through the side slots in the connec-
tor. Use care not to touch or bend the connector pins. Soil or salt
from your fingers can increase the electrical resistance of the con-
nection.
5. With the probe at room temperature (20°C - 25°C), the resistance
between the probe leads should be in a range of 2000 - 2800 ohms.
Advanced
®
Cryoscope Model 4250 User’s Guide
56
Figure 8: Fuse Replacement
Power Switch
Fuse Holder
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