SERVICING
26
7. SERVICING
This section has been included for the guidance of competent service
engineers only - preferably those trained by MSE (UK) Ltd.
7.1 Calibration Of Speed Control
Disconnect the centrifuge from the power supply Remove the instrument chassis
(see section 6.7 for removal instructions). Refit the two rubber feet temporarily and
set the centrifuge upright with the instrument panel at the front.
Connect 2 frequency metre to test points TP1 (ground) and TP2 (signal) at the
right hand side of the circuit board.
Place a correctly assembled and balanced rotor (see section 4) on the drive shaft,
close the lid and set the speed control and RV2 - PCB 'D' fully anti-clockwise, set
RV3 - PCB 'A' fully clockwise.
Switch on, turn the timer to ‘Hold’ and check that the rotor rotates slowly and the
centrifuge display indicates 100 rpm, if necessary, adjust RV2 - PCB 'A' (min
speed set) to achieve this condition.
Set the speed control fully clockwise, adjust RV1 - PCB 'A' until the frequency
meter reading matches half (1/2) that of the centrifuge display reading, adjustment
clockwise will increase the display reading whilst decreasing the meter reading
and vice-versa for anti-clockwise.
Adjust RV2 - PCB 'D' (max. speed set) so that the centrifuge runs at the highest
speed indicated on both the centrifuge and frequency meter displays.
7.2 Removal Of The Motor
Ensure that there is no rotor on the drive shaft. With the centrifuge turned on to its
back and the instrument chassis removed (section 6.7), remove the remaining
screws around the edges of the base plate. Making a note of terminations and
connections for reference, disconnect plugs and wires and remove the base-plate-
with-motor. The upper part of the motor is partially secured by the rubber support
disc in the body and can be pulled out.
Remove the three nuts and spring washers which secure the three rubber mounts
to the base plate. Remove the motor assembly from the base plate.
Remove the two hexagon screws, washers and spacers (note arrangement) and
remove the optical detector printed circuit board. Remove the screw in the lower
end of the motor and carefully remove the plastic tacho disc. The motor can now
be detached from the tacho box by removing the three small screws around the
centre of the tacho box.
Carefully note location and position of the motor support bush around the body of
the motor before removal. Remove the motor support bush and fit it to the new
motor as noted, before re-assembly.
Re-assembly of the motor to the tacho box and base plate is a reversal of removal
procedures. Ensure that the tacho disc is centred within the slot of the optical
detector. Ensure also that the three rubber mounts are not twisted during re-
assembly. Adjust balance detector as described in section 7.3.
