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Electronic Theatre Controls Inc

Unison CMd DMX Driver Replacement


Description/Explanation of Issue

  • DMX driver chips may fail when subjected to excessively high voltage. This can be caused by a power event such as a lightning strike.
  • You may need to replace the DMX driver chip if the CMd is not receiving DMX from a known working control device, or if the chip appears to be burnt or damaged.
  • If there has been damage, it is best practice to replace both the DMX driver chip (U16) and the DMX Opto chip (U17) on the dimming engine control card.

Dimmer racks without an accessible power disconnect device cannot be serviced safely.
Before removing dimmer or control modules for service, de-energize main feed to dimmer
rack and follow appropriate Lockout/Tagout procedures as described in NFPA Standard
70E. It is important to note that electrical equipment such as dimmer racks can present an
arc flash safety hazard if improperly serviced. This is due to available large short circuit
currents on the feeders of the equipment. Any work on energized equipment must comply
with OSHA Electrical Safe Working Practices. 



Before you begin
Setup a clean, well lit work area and take appropriate ESD (Electro-Static Discharge) precautions.

Tools Needed:

  • #1 Jewelers Phillips Screwdriver
  • Dual In-Line (DIL) Chip Puller
  • DMX Output Transceiver Chip (LTC485) – ETC Part # Z1458-F
  • (Optional) DMX Output Opto-Coupler Chip (6N137) – ETC Part # Z423-F



  1. Ensure power is turned off to the dimming rack.
  2. Open the door and locate the control module.
  3. Remove the CMd control processor from the Unison DR rack and place the unit on
    a clean, stable surface.
  4. With your #1 Jewelers Phillips screwdriver, remove the (4) circled screws on the
    back of the unit and (2) along the short sides (noted below) and gently pull the cover
    plate away from the processor.


  1. Orient the processor so that the LCD display is facing you.
  2. Locate the DMX chip at location U16 and the Opto Chip at location U17 of the
    dimming engine control card.


  1. With your chip puller, gently remove the DMX and Opto chips.
  2. Insert the replacement chips so that pin one is in the correct location.
Important-Icon.png Please take note of DMX chip orientation by the divot on top of the chip.

Unison Engine U16_U17 Pin1.png

Note: U17 should be installed so that pin 1 is closest to the blue components. It is very common to install both U16 and U17 in the same direction when replacing the chips. If one or both of these chips are installed incorrectly, the processor will not receive DMX and will cause a 'No DMX' error

  1. Replace lid and screws, making sure the ESD buffer strip on the upper portion of the
    lid is inside the processor.
  2. Restore the unit into the Unison DR rack. Firmly press the CMd so that you feel the
    connections are fully seated.
  3. Close and lock the Unison DR rack door before restoring power.


If you have any questions regarding this procure, please contact ETC Technical Services

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