Lights work wirelessly but not hard wired.

[Leftylampie]

Here's an odd one. I have five DMX desks and numerous fixtures all are used in mobile situations and are in excellent condition.

 

 

I have a small desk that I'm having a problem with.

 

1. The desk in question works fine both wired and wireless with all fixtures apart from some LED PAR cans.

2. The LED PAR cans work fine both wired and wireless with my other desks without issues.

3. My cables are all proper DMX cables and in good condition.

4. My wireless DMX transmitters & receivers all work fine.

 

Here's the issue...

 

When I connect one (or more) of the LED PAR cans to the desk using a DMX cable they don't work, absolutely nothing happens.

When I connect one (or more) of the LED PAR cans to the desk using a wireless transmitter/receiver they work perfectly.

When I connect one (or more) of the LED PAR cans to the desk using both the DMX cable and the wireless T/R (i.e. in series) they work perfectly.

 

So, they work perfectly when there isn't a physical connection between the desk and the PAR cans but not when there is.

 

Does anyone have any idea why?

Edited October 18, 2021 by Leftylampie

[alistermorton]

Earth loop?

[Jivemaster]

Perhaps the signal earth in the lanterns is connected to mains ground -which the DMX spec says not to.

[DrV]

You said "one or more" of the LEDs. Have you tried a different single LED? I'm just wondering if you've got a bit of leakage from an unearthed PSU at the desk and a break in the DMX reference lead (pin 1) at the LED.

[timsabre]

Agree with Dave, sounds like pin 1 of the wired DMX is not connected on the problem controller. A lot of fixtures will work without this but some won't. When you put the wireless transmitter in series it adds the ground back in.

[Leftylampie]

Thank you for your help and suggestions, it is appreciated. The desk is a class two and fed by an external PSU and, as such, doesn't have an earth (but obviously it does have a ground on the circuit board). One of my other desks is also a class two and the PAR cans work fine with it.

 

 

I have now tried the following without any success.

 

1. Taking the back of the desk to check that all of the pins on the back of the XLR output are connected to the circuit board - They are.

2. Disconnecting the screen inside the XLR Plug at the desk end - the results are the same as in my original post.

3. Tried different (identical) PAR cans - again the same result as in my original post.

 

I'm still puzzled.

[skinda0]

It's not got a DMX polarity switch has it? The wireless adapters may be clever enough to flip it at the other end.

Although reading through the rest of the trouble shooting it sounds like this may not be the cause.

Could it be these cans are a bit finicky about line termination and the wireless drivers are terminating sufficiently?

Although I may have completely the wrong end of the stick

Edited October 19, 2021 by skinda0

[Leftylampie]

It's not got a DMX polarity switch has it? The wireless adapters may be clever enough to flip it at the other end.

Although reading through the rest of the trouble shooting it sounds like this may not be the cause.

Could it be these cans are a bit finicky about line termination and the wireless drivers are terminating sufficiently?

Although I may have completely the wrong end of the stick

 

Hi, thank you for your suggestions. There is no polarity switch on the desk but I do have an XLR male to female phase reversal adapter (which I have tried).

I've also got end of line termination resistors fitted.

[alistermorton]

Can you verify that you have pins 1,2,3 respectively continuity all the way end to end, and that you don't have a pin1 to earth connection anywhere?

[timsabre]

Pin 1 to earth doesn't stop DMX working. In fact most mains-connected controllers (except class 2 ones) will have a connection between their circuit 0V (which will be connected to pin 1) and earth - probably via a resistor.

 

The reason it is not allowed by the DMX spec is to avoid large fault currents flowing down the DMX cable if something untoward gets connected to it.

 

[Leftylampie]

Yes, there are no short or open circuits anywhere, all leads and fixtures work without any issues on my other four desks.

 

Can you verify that you have pins 1,2,3 respectively continuity all the way end to end, and that you don't have a pin1 to earth connection anywhere?

 

 

 

[niclights]

My gut feeling was polarity also but the symptoms suggest otherwise.

 

Just to clarify:

 

1. Are the other four consoles a different make/model?

2. Do the other fixtures work ok on the other consoles?

3. Are the same cables being used when moving between consoles?

 

Regarding points 2 and 3 am I correct in saying the following, preferably using dimmers/individual channel control in all consoles to eliminate any patching/profile issues?

 

a) problem console -> cable 1 -> problem fixture -> cable 2 -> good fixture = problem fixture not responding, good fixture responding

b) problem console -> cable 1 -> good fixture -> cable 2 -> problem fixture = problem fixture not responding, good fixture responding

c) good console -> cable 1 -> problem fixture -> cable 2 -> good fixture = both fixtures responding

 

(where 'problem fixture', 'good fixture', 'cable 1' and 'cable 2' are the same in each)

[Leftylampie]

Hi, all five of the controllers are different makes/models.

 

All permutations of controllers/DMX leads/fixtures work perfectly well apart from this one particular desk and the PAR cans.

 

For testing purposes I set all of the cans (and some other fixtures) to start at address one and connected them both wired and then unwired to the other controllers one at a time everything worked perfectly with every controller.

 

When I connect the same 'working' wired set up to the problem controllers all of the fixtures work apart from the PAR cans, then when I add the wireless transmitter/receiver into the chain from the desk everything including the PAR cans work perfectly.

 

My gut feeling was polarity also but the symptoms suggest otherwise.

 

Just to clarify:

 

1. Are the other four consoles a different make/model?

2. Do the other fixtures work ok on the other consoles?

3. Are the same cables being used when moving between consoles?

 

Regarding points 2 and 3 am I correct in saying the following, preferably using dimmers/individual channel control in all consoles to eliminate any patching/profile issues?

 

a) problem console -> cable 1 -> problem fixture -> cable 2 -> good fixture = problem fixture not responding, good fixture responding

b) problem console -> cable 1 -> good fixture -> cable 2 -> problem fixture = problem fixture not responding, good fixture responding

c) good console -> cable 1 -> problem fixture -> cable 2 -> good fixture = both fixtures responding

 

(where 'problem fixture', 'good fixture', 'cable 1' and 'cable 2' are the same in each)

Edited October 19, 2021 by Leftylampie

[DrV]

Next suggestion is that there is something dodgy about the DMX stream coming out of the dodgy desk. Eg. Incorrect break or mark-after-break timing. You'll need a scope or an analyser like a DMXCat to check that.

Edit: Just to clarify my reasoning - desk outputs DMX which is slightly out of spec; most of your fixtures are not too fussed about it so they work; bad LEDs are actually expecting perfectly timed DMX so they don't work; wireless link retimes the DMX stream so what comes out of it is acceptable to the LEDs.

Edited October 19, 2021 by DrV

[alistermorton]

Yes, there are no short or open circuits anywhere, all leads and fixtures work without any issues on my other four desks.

 

Can you verify that you have pins 1,2,3 respectively continuity all the way end to end, and that you don't have a pin1 to earth connection anywhere?

 

 

 

 

I was thinking about "hum loops" like you can get in audio where there are multiple shells connected to earth. Clutching at straws, maybe.