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921

BRIDGE RATING FAULT

Otis · DSD 412 DC Elevator Drive

What does 921 mean?

The system is unable to identify the drive's size. The bridge type, ampere rating, and current feedback scaling are determined by a sense resistor on the Cube ID PCB, which plugs into the A2 Armature Interface PCB. This fault occurs if the computer cannot identify this physical hardware. A DSD power down is required.

Common Causes

  • J14 on the Main Control PCB is not properly seated.
  • The Cube ID PCB is either missing or an incorrect type for the drive.
  • Incorrect PCU software version is loaded in U13 & U14.
  • A faulty Armature Interface PCB (A2).
  • A faulty Drive Control PCB.

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Ensure that connector J14 on the Main Control PCB is properly seated.

  2. 2

    Verify that the correct Cube ID PCB is installed and present on the A2 Armature Interface PCB.

  3. 3

    Check that the correct PCU software version is installed in U13 & U14.

  4. 4

    If issues persist after checking connections and software, replace the Armature Interface PCB (A2) or the Drive Control PCB.

  5. 5

    Perform a DSD power down.

Browse all codes in this manual (48)
Verified technical data. Last updated: April 2026

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Source: Otis DSD 412 DC Elevator Drive
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