CDCB Replacement - Merc40

Prerequisites

Table 5. Safety

CRUSH HAZARD.
UNEXPECTED GANTRY ROTATION CAN CAUSE SERIOUS INJURY.
Never service the gantry with the axial drive enabled. Use the gantry rotation lock to lock out gantry rotation. See safety menu of Service Document gui for appropriate procedures.

Table 6. Required conditions
Condition	Reference	Effectivity
Only trained service personnel should service the GE CT Scanner.	-	-
Static strap and monitor must be used when working inside the detector.	-	-

Overview

This procedure defines the necessary steps to Remove and Install the CDCB.

Move table to home position, fully out and down.
Remove right side gantry cover.

Refer to Parts Replacement → Gantry → Enclosure → (Cover Removal Procedure).
Stop the rotor of X-ray tube in case of Liquid Bearing Tube before HVDC off. Refer to Liquid Bearing Tube Rotor stop procedure for details.
Turn OFF the Axial Drive and HVDC switches on the gantry’s Service Switch Panel.
Position the detector at 12 o'clock and lock gantry rotation.
Turn OFF the 120 VAC switch on the gantry’s Service Switch Panel.
Remove the gantry left side cover, top covers and front cover.

Cover the Tube Collimator port to protect it against dropped tools or screws. (Cloth or any other available item)
Remove the Air Plenum as shown in Detector Air Plenum Removal/Installation.
Disconnect 2 optical fiber cables from CDCB.

Figure 1. Optical Fiber Cables
Remove 6 screws holding the rear enclosure R to the DAS assembly, and remove the rear enclosure R.

Figure 2. Rear Enclosure R
Remove 12 screws holding the CDCB to the backplane of DAS.

Figure 3. Screws of CDCB

To prevent damage to connectors pins on CDCB, do not disconnect the 2 connectors on CDCB singly.

Hold the CDCB as shown in illustration below, and carefully and slowly wiggle or rock the CDCB, then disconnect the 2 connectors on CDCB from the backplane at a time.

Figure 4. CDCB Disconnection
Pull out the CDCB from the guide pins on the backplane.

Figure 5. Guide Pins

Install the new CDCB along the guide pins.
Push the backside of connectors on CDCB forward slightly, and connect them to the backplane.

Figure 6. CDCB Connection
Tighten the 11 screws to fix the CDCB to the backplane.
Install rear enclosure R, and tighten the 6 screws.
Connect the 2 optical fiber cables to CDCB.
Install the Air Plenum as shown in Detector Air Plenum Removal/Installation.
Remove the cloth or any other item from the tube collimator port.

Make sure the Axial Drive, HVDC and 120 VAC switches on the gantry’s Service Switch Panel are OFF.
Release the gantry rotational lock and install gantry covers, all except the right side cover.

Refer to Replacement → Gantry → Enclosure → (Cover Removal Procedures).
Turn on the 120 VAC, HVDC and Axial drive service switches.
Install gantry right side cover.

Perform mA Noise Check by following the steps below.
1. Launch Diagnostic Data Collection from Common Service Desktop.
2. Go to Position Tube and set tube position to 0 deg.
3. Select Static X-ray On as Scan Type and set the following parameters. Apply default unless otherwise specified.
  - Scan Time: 1.0 sec.
  - kV: 120
  - mA: 10
  - Trigger Rate: 984
  - Filter: Air
  - Slice Collimation: 64x0.625
  - Tracking Mode: Off
4. Execute a scan.
5. Dismiss Diagnostic Data Collection tool in Diagnostic tab of CSD.
6. Launch Scan Analysis in Image Quality tab of CSD and select the scanned data.
7. Select Aux Channel.
8. In Aux Channel Select window, set the view number from 200 to 984 views, select mA check box and deselect Kv. Then press OK.
9. Verify the standard deviation of mA is within the specs below. If not, replace the CDCB board. Specification: Std. Dev. ≤ 0.11.
  
  Figure 7. Scan Analysis result
Perform a [Quality Assurance Test] from the [Functional Checks] menu of the service manual to ensure system operation.