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Electronic Theatre Controls Inc

Unison CMEd, CME and CMEi Output 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. After the steps described above are carried out, the pictures will be immediately deleted without any additional confirmation queries. 


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

Tools Needed:



  1. Ensure power is turned off to the dimming rack.
  2. Open the door and locate the control module.

CMd Processor.PNG

  1. Remove the control processor and place the unit on a clean stable surface.
  2. With your 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


  1. Orient the processor so that the LCD display is facing away from you.
  2. Disconnect the CPU Interface cable, disk power connection and the disk drive data
    connection as noted below.


  1. With your screwdriver, remove the (2) screws holding the PCB to the standoffs.


  1. Locate the side locking rail on the sides of the PCB and gently push them to the
    outside and pull up slightly on the PCB to release from the slot. Pull the PCB straight


  1. Place the PCB on a flat working surface.
  2. With your chip puller, gently remove the DMX chip.
  3. Insert the replacement DMX Output Transceiver chip into the socket so that pin one is located in the correct
    1. (Optional) Repeat Step 11 for both DMX Output Opto-Coupler Chip chips.


  1. Restore the PCB into the locking rails, with the populated side facing the LCD
    display. You will need to lock the PCB in place by sliding the release levers inward.
  2. Replace the circled screws to mount the PCB in place.


  1. Reconnect the CPU Interface cable, disk power connection and the disk drive data
    connection as noted below.


  1. Replace the lid and screws, making sure the ESD buffer strip on the upper portion of
    the lid is inside the processor.
  2. Restore the CMEd to the Unison DR rack. Press firmly on the unit to ensure it is fully
    seated into its connections.
  3. Close and lock the Unison DR rack before restoring power.


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

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