• Topic ID: id_16157704
  • Version: 4.0
  • Date: May 24, 2022 2:03:50 AM

Power Unit Replacement

Prerequisites

Overview

Procedure summary:

  • If possible, upload JEDI database (from JEDI to console)

  • Remove power unit mounting screws

  • Replace power unit

  • Reattach wiring

  • Reload JEDI software and appropriate database

1 Power Unit Removal

Procedure

    • danger
    • Follow lockout/tagout procedures for power & rotational hazards.
    • Failure to lock the gantry could result in injury, should the gantry suddenly move and strike you.
    • Make sure you engage the locking mechanism before you remove the power unit.
  1. Upload JEDI database (from JEDI) if you wish to retain the existing database after new Power Unit installation. In most cases you will want to perform this step, however it may not be possible, depending on the failed KV control board. If it’s not possible, move on.
  2. Move table to its lowest elevation.
  3. Remove, and set aside, both gantry side covers, top covers, front cover.
  4. Turn OFF all 3 switches (Axial Drive, HVDC, 120VAC) on the STC backplane.
  5. Remove power at main disconnect (A1) panel. Use proper Lockout/Tagout procedures.
  6. Remove the two M12 screws from the right front gantry cover mounting bracket, remove and set aside the bracket.

    Figure 1. Support Bracket Removal

  7. Rotate the Gantry until the power unit reaches the 3 o’clock position.
  8. Engage gantry rotational lock.
  9. Cut any tie-wraps holding the cables to the power unit.
  10. Use the spanner wrench to remove the high voltage cable connector from the tank on the power unit.

    • Ground the ends of the H.V. cable to the Gantry frame, to endure no voltage exists at the end of the cable.

    • Use rags or paper towels to wipe excess oil from the H.V. Cable Connector and tank well.

    • Stuff the tank wells with paper towels to absorb any oil.

    Figure 2. HV Cable Configuration

  11. Disconnect the following cable connectors:

    • Fan Power Cable Connector

    • CT I/F J3 Connector (<-> ORP)

    • J5 Connector (<-> DAS)

    • J6 Connector (<-> Auxiliary Assy)

    • J7 Connector (<-> Power I/F)

    • PI Filter J1 (<-> Auxiliary Assy, HEMIT Tank)

    • U1, U2 (<-> Slip Ring)

    • KV Cont J3 (<-> Auxiliary Assy)

    • J14 (<-> Auxiliary Assy)

    Figure 3. Cable Connections

  12. Remove the power unit from the gantry:
      Notice Image
      • warning
      • severe injury possible.
      • if the hoist hook's lock nut is loose, then the jedi power unit might drop from the hoist, with the resulting in serious injury to service personnel.
      • before using the hoist, check to make certain that the hook's lock nut is not loose. If it is loose, do not use the hoist. instead, order a new hoist.
    1. Attach the hoist to the boom arm in the gantry.
    2. Attach the hoist lifting chain to the lifting bracket on the power unit top.
    3. Remove slack from the hoist chain.
    4. Remove the four M12 screws and one 19 mm nut that fasten the power unit to the rotating base.
    5. Use the hoist to lower the power unit to the floor.

2 Power Unit Installation

Procedure

  1. Ensure that Lockout/Tagout procedure has been applied, and that gantry power is removed.
  2. Ensure that gantry rotational lock is engaged and gantry does not rotate by attempting to rotate gantry by hand.
  3. Using the hoist, attach new power unit to gantry.
  4. Torque the four M12 screws and one 19 mm nut to the following pre-load value.
  5. Torque the four M12 screws and one 19 mm nut to the following final value.
  6. Replace the control module covers (part1 and part2) of the new power unit with the existing one.
  7. Re-connect all the cables.
    note: Follow the following procedure for tightening HV cable ring nuts.
    • Lightly wet the new rubber quad ring with transformer oil.
    • Return the quad ring to its slot at the top of the receptacle retaining ring.
    • Pour transformer oil into the receptacle approximately 13 ml (reference only, please adjust the oil amount as necessary).
    note: DO NOT use the syringe in vertical position, this will result in air bubbles which increase the chances of the high voltage breakdown.

    Figure 4. Filling Receptacle

    • Align the cable terminal orienting key with the notch in the receptacle.
    • Slowly insert the cable, to engage the connector pins, and seat the cable in the receptacle.
    note:

    After installing the cable to the receptacle, confirm the transformer oil is spilled over a little from the receptacle as shown in Figure 5.

    If the transformer oil is inappropriate amount, adjust the oil amount as necessary.

    Figure 5. Appropriate Amount of Transformer Oil

    1 HV Cable
    2 Transformer Oil
    3 Receptacle
    • Carefully wipe up all excess oil.
    • Tighten the cable locking ring by ¼ to ½ of a full turn after the gap is closed and friction is felt by hand.