2. Press STOP to raise the operating head and exit to the test menu.
3. Press STOP to exit from the test menu to “Cryoscope Ready” (if
the initial diagnostics had not been completed when the test menu
was entered, the 4250 will complete them before “Cryoscope
Ready” is displayed).
11. Event Record
This menu item displays the last 200 recordable events of the instru-
ment, and is used when servicing the instrument.
Fuse replacement
If you determine that your instrument is not functioning because of
blown fuses, you will need to replace the fuses using the following pro-
cedure:
1. Switch the power switch to the off position and disconnect the
power cord.
2. Use a small flat-bladed screwdriver or similar tool to remove the
fuse holder door. Remove the fuse holder.
3. Double-check the values marked on the fuses. The Model 4250
will automatically adjust for voltages between 100VAC and
240VAC, but appropriately rated fuses (2) must be installed. Use
5 x 20 mm, 250V, time delay (Type T): 2-Amp.
4. Re-install the fuse holder into the back of the instrument.
5. Reconnect the power cord and switch the power switch to the on
position. The instrument should start up as normal.
Sample probe checks and replacement
Glass-tipped probes are very sensitive and quick to respond but are
somewhat susceptible to pushing, pulling and bumping damage. Such
damage often causes varying electrical leakage to ground through the
sample and may usually be detected via close visual inspection or dis-
55
Troubleshooting & Service
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