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Zero 88 Alphapack 2 DMX Issues


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We've got an Alphapack 2 which seems to be very fussy about DMX signals - specifically, it won't work unless it's the only thing in the DMX chain.

When connected after another fixture, the DMX LED blinks, and if connected with another device after it (I've tested this with a dimmer pack with built in DMX termination), the DMX LED just turns off.

I've seen https://www.blue-room.org.uk/topic/32671-alpha-pack-2-dmx-problems/ and checked the firmware, it is the new version.

Anyone have any ideas?

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Just had a go with some other cables - same issue on the through connection, the DMX light just turns off as soon as something is plugged in.

Though it was happy enough being the second thing in the DMX chain, I'll put that error on the count of it being after 6 other devices without a terminator when I first found the issues.

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What make are the LED fixtures? Are they "name" brand fixtures or chinese produced?

I've had experience previously with Chinese fixtures that don't comply with the DMX standard (just enough to be DMX) and they will work happily wth controls & other fittings from the same factory but not with kit that does comply fully - like Zero88 kit. It also doesn't help if the fittings havre a 'Master/Slave" mode - this often means that the fittings are regenerating DMX however they see fit. The cynic inside me says that the chinese do this so that you 'have' to use the LED's with their controllers...

Sadly, the symptoms are never the same but mostly can be flickering, colours sticking on or other DMX kit in the data chain not working. The only way around it is to either use a DMX Buffer that regenerates the DMX signal not just amplifies it so that the waveform is crisp, timings are spot on and the signal conforms to standard - usually the £40 buffers won't do this. The longwinded fix is to run two separate cable runs - one to the LED's & the other to your dimmers - you can use a buffer just after the desk to split the output but it's important not to have the LED's and dimmers on the same data chain.

You should also as 'good practice' ensure that you have good mains earth integrity on the fittings, desk & dimmers - mains earth is also very often 'technical earth' or nought volts - if it floats high between the kit then that can also cause issues (it also needs to be noise free). Your data cables should only have pins 1 to 3 connected, they should not have any link between pin 1 and the case of the connectors (it still does happen and can itself cause issues) and the desk & fittings should ideally be on the same mains ring/spur so they share a common earth.

I'd place a sticky bun on the issue not being the AlphaPack but the LED's or other fixtures on the chain from experience :( 

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All the other fixtures are Prolights LumiPars and StudioCOBs so respectable fixtures I think, but I did also test the Alphapack output just going into an old Zero 88 Rack 6 (FLX -> Alaphack -> Rack 6 with termination on) and it still just kills the DMX on the Alphapack as before.

I should add that this testing was in a professional venue which was fully rewired a couple of years ago so I'd count on it not being a power issue!

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Sounds like there is a possible issue with the transceiver on the Alpha.

Can you take a resistance measurement across the + and - pins of the unit (does not make a difference if it s on the input or output as they are simply joint together inside the unit.

you should be seeing around 250k  ohms.


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  • 2 weeks later...

Just got round to testing it, the resistance seems fine - but going to test it I think I found the problem. Pin 3 on the input is just missing/broken off so there's no Data+, @kgallen was on the right track!

Well I'll add replacing that to the list of jobs...

Thanks all for your help.

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