Stange Demux issue

[erik10_4]

Firstly Happy New Year!

 

I wonder if anyone can offer any useful thoughts on a stange Demux (ShowTec 72 Channel Multi Exchanger) issue I have. When operating dimmer (Pulsar) channels through the demux, I noticed that several channels where a lot dimmer than others (channels 1 & 5). At first I thopught it was a problem with the dimmer but eliminated that by operating all channels normally using a standard analogue controller. The problem persists whether I send the DMX signal via PC (Magic Q) or DMX desk so DMX signal is not the issue.

 

I tested the output on the 8-pin din with a multimeter and find that, when the channels 1 & 5 are full up, only 5V is being output. The output on other channels when full up is a perfect 10V.

 

Assuming there is a problem with the demux but can't understand why this would only happen with some channels. Any ideas?

 

 

 

Regards

 

 

 

Erik

[adamharman]

Could be a wiring issue, Pulsar wire the 8 din plug differently to other manufacturers so if you've got the wrong type you might not be testing what you think you're testing.

Aren't the outputs on the showtec unit on 25 pin D connectors? In which case presumably the 8 pin din plug where you're testing it is the end of an adaptor lead. Have you tried testing the actual outputs of the unit.

[PaulDF]

Try testing the outputs of the unit under no load. Think it is pin 13 for ch1 and earth on pin 1, ch2 pin 25, ch3 pin 12, ch4 pin 24, ch5 pin 11.

Also, as you know channel 6 is working fine from your PC, try upping the DMX start address to 6 and see if you get 10v on ch1.

[erik10_4]

Mmm, pretty sure the wiring is correct for pulsar standard. I'll try to explain the setup I have, so please bear with me.

 

Using a 25 pin printer cable (which I have confirmed has 25 seperate connectors), I have created a custom project box with two 8 pin din outlets. One is wired Zero88 standard using pins 13,12.11 and 25,24,23 (and pin 1 as ground). The other is wired to Pulsar standard from pins 10,9,8 and 22,21,20 (and pin 1 as ground). Incidentally, the ground connection from pin 1 od the D-sub is shared between both output sockets.

 

When testing, I do not have my Zero88 connected to the Zero outlet .I am simply plugging the Pulsar dimmer into the output wired to the Pulsar standard so actually, when I refer to channel 1, this is channel 7 I am outputting from the desk and channel 5 is actually channel 11 on the desk (or Magic Q). Are you still with me?

 

Obviously I could have made an error in the wiring but it seems stange that I would get output on all the expected channels (albeit at the wrong voltage on two of the channels). The measurements I took were directly from the din plug so I could try taking measurement from the 25 pin socket itself (good thought).

 

Although not 100% confident with my wiring, is it likely that I would get some output on the expected channels if I had got this slightly wrong? The signal is there...just at the wrong voltage.

 

Totally confused. Is there any way of making sure that all demux 'memories' are cleared?

Regards

 

Erik

[adamharman]

Ok, you're only really likely to get strange results if you've swapped the ground connection with one of the channel outputs although the dimmer probably chucks out +20v on one pin to power a small desk so feeding that back into the demux could be interesting!

 

If you've got a nice smooth 0-5v instead of 0-10v then it's probably either a demux fault or the settings. Not sure how clever the showtec one is, you may be able to set the output voltage (in which case you'll get 5v at 100%) or a top limit (you'll get 5v at 50% and it won't go higher) for the individual channels. A read of the manual is required I reckon!

 

Edit to add:

 

Found the manual here: http://www.enlightenment.co.uk/pdfs/showtecManuals/Multi-Exchanger%20Manual.pdf

Apparently it doesn't do anything clever, the output settings are global, and set by dip switches so that rules out that possibility.

Have you tried plugging into channels 25-48 instead and see what happens there? If that works then it looks like you may have a faulty demux.

[erik10_4]

Thanks for the input people. Everything working fine now . Having double checked wiring and found it to be OK I reconnected demux this morning and there has been absolutely no issue! All channels are reacting normally after rigerous testing.

 

I'm totally baffled as, in effect, all I have done is leave the demux unplugged for a few hours and plugged it in again. I don't know whether it is possible that the unit was storing some preset channel values (it does have a store facility) which have been cleared by leaving it unplugged for a while but if not, it will remain a mystery.

 

Regards

[DrV]

Thanks for the input people. Everything working fine now . Having double checked wiring and found it to be OK I reconnected demux this morning and there has been absolutely no issue! All channels are reacting normally after rigerous testing.

 

I'm totally baffled as, in effect, all I have done is leave the demux unplugged for a few hours and plugged it in again. I don't know whether it is possible that the unit was storing some preset channel values (it does have a store facility) which have been cleared by leaving it unplugged for a while but if not, it will remain a mystery.

 

Regards

 

I see you have got it fixed now but you might want to check for a possible intermittent short between channels 1&5 as you would get precisely these symptoms if they were shorted together. If either channel was at full and the other at zero then you'd get half the voltage (assuming the drivers sink and source at the same impedance) and if they were both at full or both at 0 then you'd get full or zero correctly.

 

Dave

[erik10_4]

Thanks for the input people. Everything working fine now . Having double checked wiring and found it to be OK I reconnected demux this morning and there has been absolutely no issue! All channels are reacting normally after rigerous testing.

 

I'm totally baffled as, in effect, all I have done is leave the demux unplugged for a few hours and plugged it in again. I don't know whether it is possible that the unit was storing some preset channel values (it does have a store facility) which have been cleared by leaving it unplugged for a while but if not, it will remain a mystery.

 

Regards

 

I see you have got it fixed now but you might want to check for a possible intermittent short between channels 1&5 as you would get precisely these symptoms if they were shorted together. If either channel was at full and the other at zero then you'd get half the voltage (assuming the drivers sink and source at the same impedance) and if they were both at full or both at 0 then you'd get full or zero correctly.

 

Dave

 

That's very interesting Dave, and I think you may be right. Those two channel pins are next to each other on the socket for the Pulsar standard so perhaps when I removed the outlet socket to check the wiring this morning I inadvertently cured the short.......but as you say, it may indicate a bit of sloppy wiring which could recur. I will tidy things up and insulate between pins to make sure it doesn't happen again. Too much soldering yesterday may have made me less cautious than usual . Many thanks.