Control/Dimming need help wiring an older CD80AE dimmerpack for DMX

[sammynwa]

I volunteer at a small community theater in my hometown, and recently, our almost 20 year old Strand MX lighting controller failed beyond repair. The Arts Center has purchased a replacement controller.(an ETC Smartfade) We have 4 Strand CD80 6K dimmer packs that have the digital dimmer controllers in them allowing for control via AMX or DMX. The old Strand console used AMX, the new ETC only has DMX output.

Inside each dimmer pack, is a control terminal strip that the AMX cabling from the booth was connected to, I have been unable to locate any diagrams or instructions of how to, if it's possible, to utilize the terminal strip for inputting DMX into the dimmers. As you can see in the pictures below, the AMX signal was connected to pins 1-4. The new controller works great when plugged directly into the XLR connectors on the front of the dimmers.

Can anyone tell me if I can connect my DMX signal via this terminal strip?

If so, to which contacts do I connect the DMX data wires and ground?

Thank you for any assistance.

David

 

[FMEng]

It does not look like the DMX input is available on the terminal strip. I think you will have to use the XLR connectors on the front. As I recall, the terminal strip would get whichever protocal the buyer specified at the time of ordering. Besides, the cable used for AMX is not suitable for use with DMX512, so you will have to pull new in.

 

[jstandfast]

I'm pretty sure FMEng is right on both counts, certainly on the control wiring issue. Depending on the details of your cabling situation, a DMX>AMX protocol shift in the booth might be your
cleanest, quickest(albeit retro) way out of this.

 

[sammynwa]

Thanks for the advice! I'm actually hoping to reuse the existing cable from the booth as it IS shielded twisted pair with a drain, not UTP, as would have been originally specified for cabling AMX.

 

[jhochb]

Good Morning Sammynwa

If you can trace the DMX line from the front panel back, you may be able to find it landing point.
The XLR has to land somewhere.

Before you stick your head too far into the rack PLEASE power down the system.

Once you find where DMX terminates you only have 2 wires & a shield wire.

AMX & DMX cabling are not the same. Just being twisted pairs does not mean they are the same.
DMX spec’s 120ohm / 15pF cable if you use AMX cable you may have issues / instability.

 

[sammynwa]

I work with electronics at my day job, including high voltage stuff, so yes, I have been very careful about making sure the packs were off BEFORE putting my hands or any tools inside. I did try to trace the DMX from the front XLRs to the board-edge connector that the control terminal strip was connected to, but had no success. I'm going to guess the jacks on the front are probably opto-isolated.

I opted to terminate the cabling coming from the booth to a 5pin DMX jack, and daisy chain the packs from there with short pre-made cables. I also found the original line drawing diagram from the install in 1993, and although I was unable to find any markings on the cable itself, they actually had it marked as "Belden 8723 DMX control cable" I installed another 5pin DMX jack on the other end in the control booth, connected the board and tested. It all seems to be working great.

Thanks again to everyone for the advice.

 

[FMEng]

I'm glad you got it working. Do keep in mind that Belden 8723 is NOT impedance matched for DMX. If the system experiences any aberrent behavior, it is likely a cable mismatch. Also, the last pack in the string needs to have a 120 ohm termination. The nature of DMX is that sometimes people get away with incorrect cable or missing terminations, and sometimes it sneaks up and bites.

 

[sammynwa]

I did install our ETC Response AMX/DMX converter last in the line, and turned on the DMX termination on it. We only use 50-60 circuits, and have no intelligent lighting, so there's not really a lot of traffic on the DMX network. I'm going to keep a close eye on it during our next production, and if any dimmers seem to be misbehaving, we'll replace the cabling from the booth.

Thanks again for the responses and advice,

David