Heat Exchanger Power Supply Replacement

Prerequisites

Table 2. Tools and test equipment
Item	Quantity	Effectivity	Part number	Manufacturer
3mm hex wrench and hex end socket	1	-	-	-
Small flat head screwdriver	1	-	-	-
6 in. long 3mm ball hex bit and 6 in. long 1/4 in. hex drive - purchased locally (refer to	1	-	-	-

Table 4. Safety

electrocution hazard
voltage present in gantry
use proper lockout/tagout procedures from the safety section of the service documentation when stated during procedure. This procedure includes work directly in the gantry power pan.

Overview

This procedure describes the steps necessary to install a heat exchanger power supply assembly onto the VCT gantry.

This procedure uses many screw, lock and flat washer combinations. Make sure the order of installation has the lock washer positioned between the flat washer and head of the screw.

Remove gantry right side cover and disable Axial drive, HVDC and 120VAC service switches from the service switch panel.

Refer to Replacement > Gantry > Enclosure > Cover Removal Procedures.
Remove the gantry top and left side covers, scan window and front cover. Connect the cover E-stop circuit to the terminators on the gantry.

Rotate the gantry so that the power supply is in the 6:00 position. Refer to Figure 1.

Figure 1. Gantry Position
Loosen inner screws on the right side wires of power supply; insert a flat head screwdriver down through the top slot and remove wires from the assembly. Refer to Figure 2. Take care not to completely remove the screws.

Figure 2. Power Supply Wires

note:
To remove left side cables, slide power supply to the right to access with a screwdriver.
Remove the four (4) screws on the bottom of the power supply with a 3mm hex wrench. Refer to Figure 3

Figure 3. Mounting points of Power Supply

note:
Use care when removing the 4 mounting Screws. See Illustration below: Spacer washers are located under the power supply typically only three corners require this spacer/washer. Save the washers for reinstall.

Figure 4. Spacers
Slide power supply to the right side to access the left side wires and remove using the same method as the right side wires. Refer to Figure 2 and the corresponding note for details.

Set new power supply on bracket and slide to the right so that the left side cable connections can be accessed with a screwdriver. Connect the left side wires by inserting cables into the power supply between the head of the screw and the board. Tighten the screw using a flat head screwdriver. Refer toFigure 5 (left) for wire position.

equipment damage possible
loose components can come off if not secured properly
Failure to follow the instructions in this procedure as defined can cause a component to become loose later.

Slide power supply into correct position and bolt onto the gantry at the same four (4) points as the old supply. Refer to Figure 3. Torque front two (2) bolts according to Table 6. Reinstall spacer/washer if removed earlier.
Table 6. Power Supply Torque Values
1.5 N-m 13 lb-in 1.0 lb-ft 15 kg-cm

The two (2) back bolts are hard to get to if you do not have the recommended tools, 6 in. long 3mm ball hex bit and 6 in. long 1/4 in. hex drive. Either of the following 2 steps can be used to tighten these two (2) screws.
- Preferred Method: Using a 3mm (6 in. long) hex bit and 1/4 in. (6 in. long) hex drive, torque according to Table 6.
- Alternative Method: Using a 3mm hex wrench, seat the screws then continue to turn 1/4 turn to apply sufficient torque. Do not over tighten. Use approximate force applied to torque the other two (2) screws as a guide to the force limit for these two (2) screws. If either screw strips out, you will need to order a new supply. Do not allow operation of the system with stripped mounting screws.
  
  note:
  Do NOT use this alternate torque method anywhere else in the system unless specifically defined by the service procedure.
Use a screwdriver to reconnect the right side power supply wires to the power supply. Refer to Figure 5.

Figure 5. Wire connections to power supply

Install the gantry front cover, scan window, top and left side covers.
Turn on the Axial drive, HVDC and 120VAC service switches from the service switch panel.