Thermo IEC Micromax 3590, Service Manual, Page: 42 / 84

7. Turning the unit on its side*, remove the 4 screws from
the motor mounting plate. These are accessible
through the hole in the unit’s base plate.
8. Partially lift the motor out through the opening in the
guardbowl.
9. Reach through the opening in the guardbowl and
disconnect the motor ground wire from the base of the
motor.
10. Replace the motor in the same fashion, reversing the
steps.
*Caution: On RF models, once the centrifuge has been turned over
on its side, and the returned to its normal position (on all
four suction cup feet) it must be allowed to stand for 24
hours before use. Serious refrigeration system damage
can result if the compressor oil is not allowed to completely
settle.
11.2
Speed Sensor
The Speed sensor is a set of three hall effect type sensors
located at the bottom of the motor. It does not require
calibration or adjustment. Its accuracy (+/- 10 rpm) can be
verified by strobing the motor shaft through the viewport in
the cover. It is integral to the motor and replacement
requires replacement of the motor as a unit.
The sensor(s) and magnetic disk can be inspected by
removing the cover at the bottom of the motor (2 screws).
This sensor indicates not only the speed of rotation, but
also position of the armature for the powering of the three
phases at maximum efficiency. The sensor disk should
not be loose, with respect to the shaft. This disk is
mounted and fixed to the motor shaft at a specific location,
and is synchronized to the armature. If its location (relative
to the shaft) has changed, the motor will be misfiring and
unable to attain maximum speeds. This requires
replacement of the motor, as synchronization in the field is
not possible.
The sensor(s) are located on the small printed circuit board
within the motor. All three should be located with good
proximity to the magnetic disk. If any gap appears to be
too great the sensors can be carefully manipulated back
towards the disk. Take care not to locate them too close,
as the disk may rub on and damage them.
Micromax Series
40
Service Manual