• Topic ID: id_18718264
  • Version: 2.0
  • Date: Feb 4, 2020 1:40:30 AM

GDAS(4/8) Detector Thermistor Replacement

Prerequisites

Procedure

  1. Verify that you have all the parts/tools required.
  2. Turn off 120VAC Gantry Power.
  3. Disconnect Detector Cable at J3.
  4. Remove Thermistor wires/pins from J3 connector. These are the Red and Black wires. Note their location within the connector. Use Pin extract tool.

    Figure 1. J3 connector, showing thermistor wires

  5. Verify correct old Thermistor wires, then cut the old Thermistor cable close to where the Thermistor cable and Detector Heater cables are joined in the shrink-wrap sleeve. Do NOT cut the Detector Heater wires.

    Figure 2. Approximate location for cutting thermistor wire

  6. Unscrew the Thermistor wire “Hold-down clamps”. There are two (2): one is near the end of the detector, the other is near the Thermistor.
  7. Carefully peel back the EMC tape covering the Thermistor wire so the wire is free.

    Figure 3. Remove old thermistor

  8. Unscrew and remove the Thermistor using a 9mm open-end wrench.
    9. Notice Image
    • notice
    • Make sure no dirt or debris gets into the detector through the open hole.
  9. Make sure the new Thermistor is clean before installing (No lint, dirt, debris, etc.)
  10. Screw in the new Thermistor until snug. Use finger pressure on wrench. Do not over-tighten. The metal Thermistor housing is only a shell. The wire should be free so it does not get twisted.
  11. Route the wire along the detector side just like the old wire, against the inner radius of the Heater element.
  12. Use EMC tape or Conductive tape to cover the wire.
  13. Secure the wire with the 2 “Hold-down” wire clamps. Make sure the wire is properly positioned at the Thermistor so it doesn't interfere with the DAS Fan Air Plenum, and that the wire isn't too tight, creating a sharp bend at the detector. It should also not be so loose as to get caught or rub on anything during rotation.

    Figure 4. Route new thermistor cable

  14. Route the wire along side the Shrink-wrapped cable going to J3. Ty-rap the new cable to the outside of the shrink-wrapped cable.
  15. Install the pins of the wire into the J3 connector.
  16. Connect J3 and confirm that any excess wire is secure and out of the way.

Finalization

  1. Wait at least one (1) hour with power ON for the Detector to warm up.
  2. Verify detector temperature is 36 degrees Celsius
  3. Perform FastCal.
  4. Perform Image Quality Test Procedures. Take several scans for a couple of hours so that you are satisfied that the problem has been corrected.