Hologic DISCOVERY A, Technical Manual

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Discovery QDR Series Technical Manual
5-39
3. Remove 6 screws from underneath the drum assembly base plate (4 screws hold
the end plates and 2 screws hold the motor mount spring tensioner block).
4. Remove the side plates and lead shields (3 Phillips screws on each side).
5. Remove the drum encoder PCB and both encoder wheels.
6. Remove both drum belt pulleys.
7. Remove the drum from the endplates.
8. Remove one drum endcap (4 Phillips screws) and remove the inner drum.
9. Replace the bearings.
10. Reassemble the drum and replace (and tighten) the screws in the endcap.
Note: When replacing the end cap ensure that the flats on each side of the drum
shaft are facing the same way (this happens where the two side-by-side
holes line up).
11. Replace the 2 endplates. The endplate with the cutout (for the PCB) goes on the
drum end away from the alignment hole (see Figure 5-21).
12. Replace the lead shields and side plates (6 screws).
13. Align the 2 endplates onto the holes on the recessed area on the base plate. Orient
the front endplate towards the 2 slotted holes. Orient the rear endplate on the
opposite set of holes and position so that the endplate side with cutout (for PCB)
is facing the "C" cutout of the base plate. Replace the 4 flat washers, split locks,
and 4-40 x 3/8 screws that secure the endplates.
14. Insert the Drum Spacing Fixture (099-0296) between the endcap and the front
endplate. Push the filter drum against the fixture to center it between the two
blocks. Do not remove the fixture at this time.
15. Install the spacers and pulleys at the front endplate (see Figure 5-18). Ensure that
the pulley set screws line up with the flat, and use Loctite 222 on set screws.
Press the filter drum against the fixture, and the pulley against the endplate, while
tightening the set screw.
Note: Leave the outer pulley set screw loose until belts are installed.
16. Remove the Drum Spacing Fixture.
17. Replace the inner encoder wheel (see Figure 5-17). Press (squeeze together) the
drum and encoder wheel against the endplate and tighten the set screw (use Loc-
tite 222).
18. Replace the outer encoder wheel.
19. Replace the drum encoder PCB. Ensure that the encoder wheels do not contact
the sensors.
20. Replace the stepper motor assembly (2 screws on the motor mount, and 2 screws
on the base plate). Leave the motor mount screws loose for now.
21. Replace the drum belts (see the Drum Belts procedure).
22. Tighten outer pulley set screw after belts are installed.
23. Refer to the Aperture Assembly procedure and install the aperture assembly.