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Electronic Theatre Controls Inc

DMX Port Not Working on Response Opto or I3M


One or more DMX ports are not functional

Explanation of Issue

It is likely a DMX chip and/or an opto-isolator has failed, often caused by an external event.

If the opto-splitter is not receiving DMX at all, it is likely the DMX chip at Z1 has failed

If one or more of the DMX ports at A, B, C, D, or E have failed, it is likely the DMX chip has failed. If replacing the DMX chip does not restore DMX for that port, the opto-isolator should also be replaced. All chips on the Opto-splitter are socketed for ease of replacement

Each port also has two fuses for the differential pairs. These should also be checked for continuity, though they rarely fail

The following chart is for the Response Opto-splitter I5M

Port DMX Chip Location Opto-isolator Location Fuses
A Z5 Z4 X1, X2
B Z8 Z7 X3, X4
C Z11 Z10 X5, X6
D Z14 Z13 X7, X8
E Z17 Z16 X9, X10

The image below shows the location of the DMX chips (circled in red) and the opto-isolators (boxed in yellow)

RSVP I5M Overview Draw.jpg

Port Information

There are two legacy/classic Response Opto-Splitters, the I3M and I5M. The I3M has three (A, B, C) optically isolated DMX ports, and the I5M has five (A, B, C, D, E).
The DMX-In port is not isolated. The DMX-Through port is tied to DMX-In and is also not isolated.


  1. Remove the Response Opto-splitter from mains power
  2. Open the chassis. There should be four Philips head screws
  3. Find the DMX chip for the problem port
  4. Replace the DMX chip
    1. If replacing the DMX chip does not restore DMX, replace the opto-isolator for the problem port
  5. Replace the cover (don't have to screw down the cover yet and plug back into mains power
  6. Test the problem port


Parts can be purchased through ETC or through an electronics distributor, such as Digikey or Mouser (in the United States)

Part ETC Part Number
DMX chip - 75176 (old style, not available from ETC)  Not Available (Formerly Z216-F)
DMX chip (new style, available from ETC) Z1458-F
Opto-isolator Z423 or Z423-F
Fuse (0.125A, 250V, 5x20mm) F113-F


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