4.03
Lid and Coil Assembly
(Cont’d)
There are two openings in the end of the coil housing. The round opening (Diagram “C” item
30), lined with a phenolic tube, is the center of the magnetic coil; a vial is placed here for
grinding. The larger rectangular opening (Diagram “C,” item RO) above will hold two vials for
pre-cooling (cooling vials prior to grinding).
NOTE: Never touch the coil housing with bare fingers if liquid nitrogen is in use.
The gate (Diagram “C,” item CG) holds the vial in place, in the coil, during grinding. When the
lid is closed, the gate shuts automatically. When the lid is raised and a vial is in the coil, the coil
gate will occasionally stay shut and must be opened manually. (Always wear gloves when
touching a chilled vial or any part of the chilled coil housing!) To open the gate, pull the gate
handle (Diagram “C,” item GH) down; it will lever the gate open. The roller on the coil gate
handle allows it to retract smoothly into the tub when the lid is being closed.
When you shut the lid, push it down gently, and the coil gate will close. Never force the lid
down strongly against resistance, in case the coil gate is jammed.
The liquid nitrogen sensor (Diagram “C,” item 28) is the small cylinder with wires attached, on
the side of the coil housing nearest the hinge. If the liquid nitrogen level in the tub falls to the
point where the coil might be damaged from overheating, the control display will flash “LN”,
the fault indicator will blink, and any grinding cycle in progress will be aborted. To restore the
control display, fill the tub with liquid nitrogen to the mark, and press ENT. When RUN is
pressed, the grinding program will start over.
NOTE: To keep a run from being interrupted by the liquid nitrogen (LN) sensor, the LN level
should be visually checked during extended runs as well as before every run. The 6750
Freezer/Mill will run out of LN after about 20 minutes of actual grinding time, so it is imprudent
to run programs with longer grinding time. The Freezer/Mill warranty does not cover damage to
the coil caused by operating the mill with little or no liquid nitrogen.
It is possible to test the 6750 Freezer/Mill without liquid nitrogen for a period of several seconds,
by putting a 6751 vial in the mill and pressing the MAN key after the LN sensor has been
disconnected. Uncouple the pneumatic cylinder from the lid, open the lid all the way, and
remove the four screws holding the lid cover. Carefully shut the lid and latch it. Remove the lid
cover, and disconnect the LN sensor. This connector is at location P1 on the main board, on the
far right corner of the board; its wires are blue and white. Replace the lid cover and press the
MAN key; you should hear the clicking of the impactor moving back and forth. Re-attach the
connector, lid cover, and pneumatic cylinder before operating the Freezer/Mill with liquid
nitrogen. A more detailed description of this procedure is in Appendix 1 on page
Page 7 of 28
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