• Discovery MR750 3.0T System Service Methods
  • 5690009-2EN Revision 4
  • Object ID: 00000018WIA30551130GYZ
  • Topic ID: id_12373821 Version: 1.6
  • Date: Oct 30, 2020 8:53:59 AM

XRMB Cable Busbar Replacement

Prerequisites

Table 1. Personnel requirements
Required personsPreliminary requirementsProcedureFinalization
23 hours5 hours3-4 hours hours
Table 2. Tools and test equipment
ItemQuantityEffectivityPart numberManufacturer
PPE: non-magnetic safety shoes, safety glasses, and gloves1---
Arc Flash PPE1---
Torque Wrench, 8-50 N m Adjustable, non-magnetic1-5534134 or 5534134-2 -
Non-Magnetic Tools1-

5112581

-
Table 3. Consumables
ItemQuantityEffectivityPart numberManufacturer
Blue Loctite 243 (check expiration date)1-

5415261-2

-
Alcohol wipesAs needed---
Scotch Brite pad1---
Black Sharpie pen1---
Nylon Tie WrapsAs needed---
Table 4. Replacement parts
ItemQuantityEffectivityPart numberManufacturer
XRMB Cable Busbar1-

See FRU Manual

-
Busbar Step Gauge (part of FRU)1-

See FRU Manual

-
Table 5. Safety
Table 6. Required conditions
ConditionReferenceEffectivity

At least one person performing this procedure must have taken training course GEHC-TECH-AMOL-CT530-01_CURR.

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About this task

Overview

This procedure describes the replacement or installation process for the eXtreme Resonance Module Revision B (XRMB) busbar (cable version) in the MR750 3.0T magnet.

Topic ID: id_SL12748592-1067540

Getting Started

Procedure

  1. Order the non-magnetic torque wrench before starting this procedure.
  2. Follow all safety lockout/tagout procedures.

    • Perform LOTO on the PGR PDU/gradient subsystem. See the MR Service Safety Manual, PN 5452735.

    • Perform LOTO on the RF amplifier and PEN cabinet (magnet room electronics). See the MR Service Safety Manual, PN 5452735.

    Note:

    Do not shut down the cryogen cooling system.

  3. Remove the patient bridge. See Bridge and Longitudinal Drive Belt Replacement.
  4. Remove the magnet enclosure rear end bell. See Rear End Bell Removal and Installation.
  5. Move the rear pedestal away from the magnet.
    Note:

    There should be two feet of cable in the service loop. This excess cable allows the rear pedestal to be moved back without disconnecting cables; however, it is possible that some cables may need to be disconnected.

Topic ID: id_SL12749967-1067540

Remove XRMB Gradient Busbar Cables

Procedure

  1. Remove the two M8x12 mm stainless steel screws and remove the XRMB busbar safety cover. Do not discard the white flame-retardant material or the fasteners.
    Figure 1. Busbar Safety Cover
    Item Description
    1M8x12 stainless steel screws and M8 nylon flat washers
  2. Remove the six nuts and Nord-Lock washers that are securing the busbar lugs.

    Discard the Nord-Lock washers and stainless steel flange nuts.

    Figure 2. Removing Nuts and Nord-Lock Washers
    Item Description
    1Six (6) stainless steel nuts and Nord-Lock washers
    Note:

    DO NOT remove the clamps on the busbar leads.

  3. At the top of the busbar, remove the five M6 stainless steel screws and the clear plastic cover.
    Figure 3. Fasteners Holding Clear Plastic Cover
    Item Description
    1Five stainless steel screws
  4. Loosen the retainer blocks to allow slack in order to remove the gradient power terminals from the busbar.
  5. Remove the 12 stainless steel nuts and Nord-Lock washers securing the gradient power cables to the busbar terminals.

    Discard the stainless steel nuts and Nord-Lock washers.

    Figure 4. Disconnecting Gradient Power Cables at Top of Busbar
    Item Description
    1Twelve stainless steel nuts and Nord-Lock washers
Topic ID: id_SL2183379-1067540

Remove Busbar

Procedure

  1. Remove the four brass nuts, G10 flat washer, and rubber isolators securing the busbar assembly to the magnet. Remove the tie-wraps securing the manifold hoses to the busbar. The busbar may look like either of the next two pictures.
    Figure 5. Busbar Mounting Points
    Figure 6. Busbar Removed
  2. The busbar can now be removed from the magnet.
Topic ID: id_SL2183393-1067540

Install New XRMB Busbar

Procedure

  1. Inspect the gradient terminal lugs for threadlocker residue. Clean with a nonmetallic brush and wipe the threads clean with alcohol.

    Use a clean nut to check the threads. The nut should thread freely with no high resistance points. Repeat procedure on each lug as required.

  2. At each busbar support stud, install the large G10 flat washer (32 mm OD, 5268439) and one rubber isolator.
    Figure 7. Busbar Support Studs (a) and Washer/Rubber Isolators (b)
  3. Remove the new busbar assembly from the busbar shipping crate.
    Note:

    Before installing the replacement busbar, inspect the surface that connects the gradient coil and cables for oxidation. If the surface is oxidized, clean the surface.

    DO NOT lift the busbar assembly by holding the leads.

  4. Align the six busbar lugs with the XRMB coil terminal studs, and smoothly push the lugs onto the terminal studs. Meanwhile, slide the busbar assembly onto the four busbar support studs Figure 9.
  5. If absent, install the grounding cable, PN 5189441-2.
    Figure 8. Placing Busbar Lugs on Terminal Studs
    Figure 9. Placing Busbar on Support Studs
  6. Ensure that the loose ends of the grounding cables can be accessed when the busbar is replaced.
    Figure 10. Accessible Grounding Cables
  7. After the busbar is mounted, place one rubber isolator, one large G10 flat washer (32 mm OD, 5268439), one M10 x 24 mm washer (5146169), and one brass nut at each of the four mounting studs. The step of the rubber isolator faces inward.
  8. Gradually tighten the four brass nuts until the height of the G10 washer surface (front side) reaches 7.2 mm. Use the step gauge (part of the busbar FRU) to verify the height of the G10 washer. Verify the busbar lugs are not hung up on the stud threads.
    Note:

    The step gauge is required to prevent stress fractures on the gradient lead terminals.

    Figure 11. Checking G10 Washer Height Using Step Gauge
Topic ID: id_SL2183401-1067540

Install Busbar Cables

Procedure

  1. At the top of the busbar, connect the 12 gradient power cables to the busbar terminals and secure them using one nut and one Nord-Lock washer at each of the terminals. Use the torque wrench to tighten the nuts on the top of the busbar to 25 foot-pounds (33.9 Nm). Read the following steps prior to using the torque wrench.
    Figure 12. Connecting Gradient Power Cables on Top of Gradient Coil
  2. Place a new Nord-Lock washer over each stud.
    Note:

    Observe the following:

    • Always use the new Nord-Lock washers that come with the FRU package. DO NOT reuse the old Nord-Lock washers.

    • Nord-Lock washers consist of two pieces, which are generally glued together. Always use a complete set with two pieces joined together in correct orientation. DO NOT use a separated single piece. If the Nord-Lock washers are separated, or the nuts are untightened, discard the washers and replace them with new Nord-Lock washers only. If new Nord-Lock washers are not available, contact the online center for further instructions.

    • Always shake Loctite bottle before use.

    Figure 13. Nord-Lock Washers
    1Wrong (do not use separated washers)
    2Correct
  3. Put two drops of Loctite 243 on the exposed thread of the terminal stud.

    Do not get Loctite on the Nord-Lock washer.

    Discard the old stainless steel nuts and washers.

    Figure 14. Loctite on Stud
    Item Description
    1Bus bar terminal lug
    2Loctite on stud
    3Nord-Lock washer (installed after lug)
  4. Hand-tighten the new stainless steel nut on the stud.
  5. Set the torque wrench to 25 foot-pounds (33.9 Nm). Install 15 mm socket on the extension.
    Note:

    Make sure that the arrow on the torque wrench is visible. If the arrow is not visible, the torque wrench will not “click” when the proper torque is reached.

    Figure 15. Arrow on Non-magnetic Torque Wrench
  6. Torque the nut in the direction of the arrow until the torque wrench reaches the break point.
    Note:

    Proper torque to the nuts holding the busbar lugs is critical to the long-term stability of the gradient subsystem.

  7. Using a Sharpie pen, place a line from the base of the stud to the nut.
    Figure 16. Stud and Nut Marked to Show Torque Position
  8. Repeat this for all the stainless steel flanged nuts.
  9. Perform a second torque operation at each nut to confirm the proper torque of the nut. (Twice for each nut.)
  10. If the nut has moved more than one flat from the original position, you must re-torque for a third time.
  11. If re-torqueing is necessary, remark the torque position (line) on the nut and stud.
  12. Secure the gradient cable guard (clear plastic cover) using five M6 stainless steel screws. See Figure 3.
  13. Install the busbar cable terminal lugs on the lower portion of the busbar as shown in Figure 16.

    Follow the instructions in Step 2 through Step 11 using a 15 mm stainless steel nut.

  14. Install the safety cover and white flame retardant material.
    1. Inspect the flame-retardant material (white cloth) for tears or internal damage. Replace safety cover if liner is damage. See FRU list for part number.
    2. Confirm that the material extends just beyond the edge of the safety cover on all sides. See Figure 1.
    3. Inspect each M8x12 stainless steel screws and remove any old threadlocker residue with alcohol, as necessary.
    4. Apply one drop of Loctite to the thread of each M8x12 stainless steel screw.
    5. Tighten the two M8x12 mm stainless steel screws.
  15. Secure the manifold hoses to the busbar using nylon tie-wraps.

    Inspect and ensure there is no contact between the safety covers and the manifold hoses.

  16. If the hoses on the left side of the busbar are uneven, use a Push-Lok Hose, PN 5394470 and Kynar hose barb, PN 46-294167P103 to help bring them to the same length.
    Figure 17. Tie-Wrapping Manifold Hoses to Busbar and Applying Ground Wires
    Figure 18. Applying Ground Wires by Hose Clamp to Manifold Fittings
    Figure 19. Final Position of Manifold Hoses
Topic ID: id_15268108

Finalization

Procedure

  1. Reposition the rear pedestal.
  2. Install the magnet enclosure rear end bell. See Rear End Bell Removal and Installation.
  3. Install the patient bridge. See Bridge and Longitudinal Drive Belt Replacement.
  4. Replace all covers that were previously removed.
  5. Remove lockout/tagout (LOTO) to the PGR PDU/gradient subsystem and the RF amplifier in the PEN cabinet. See the MR Service Safety Manual, PN 5452735.
  6. Execute DQA scan in all three planes to verify proper geometry. See DQA II Tool and Troubleshooting.