Control/Dimming Dimmer Pack Flickering

[Les]

I just got some DMX cable to test my new-used EDI Bijou, and while everything on the board seems to work great, I have one dimmer pack that is flickering.

Here's the setup:

The Bijou is connected to dimmer pack#1 (1-4) which is daisy-chained to dimmer pack#2 (5-8). These dimmer packs are new to me also, having never used them before. They are ETA MD460DMX-24's and were given to me by a tradeshow booth warehouse that was doing some cleaning.

Dimmer pack #2 is the one giving me issues. The load isn't much - 4 par16's. What it's doing is when any of the lights are on (at any level) they will flash off and on in unison. it's a very quick flash -- like the blink of an eye. It does this pretty randomly, but you could probably count on 1-2 flashes every 30 seconds or so.

I also unplugged pack 1 and plugged the offending pack directly into the board using the cable that was originally first in line (between the console and the 'good' pack). The problem persisted, so I'm pretty sure that the dimmer pack is at fault.

Admittedly, the cable I'm using isn't the absolute best - it's HOSA brand, 20' 5-pin - fresh off ebay. I bought the cheapest I could find for test purposes, but I don't really suspect the cables either.

 

[TimOlson]

first off, one of these lil' testers:

Doug Fleenor Design - DMX512 Line Tester

affordable, and worth every penny.

there's all sorts of stuff to try, even with no tester

-) terminate the offending dimmer.

-) change the address and see if the problem moves. if it does there may be an issue with the console OR with the decimal switches used to set the DMX address.

-) add more load to the dimmer and see if the problem goes away. if it does then the dimmer needs to have the trigger level tweaked.

-) try using a different length of DMX cable. sometimes noise on the line can find a resonant frequency (termination would help this a lot, too)

-) the one cut-sheet I could find indicates that this dimmer can be configured for single or 3 phase operation - it may not be set up properly for the power you have.

-) if you're really strapped for cash, google up all the references for using cat 5 cable to run DMX - it works great and can be a cheap way for you to build your own cables.

as far as tech support - good luck. ETASYS.Com quit dealing with lighting devices in 2005, and a web page there directs one to an aircraft welding company if you want truss.

here are some links that might get your goggle on:

DMX512-A - Wikipedia, the free encyclopedia

http://etasys.com check the discontinued products section

www.lighting-association.com/features/dmx.pdf an interesting article about DMX and using DMX on Cat 5 cable

peace, and good luck.

Tim O

 

[David Ashton]

Increase the load first, that is most likely to be the problem ,then try the other options.

 

[Les]

Thanks for the tips guys.

I'll plug in some 360Q's or 65Q fresnels tomorrow and report my findings. The dimmers aren't terminated so I'll look into that as a possible issue. These are running at 120v (with a factory installed cord and molded Edison plug - however the packs can be hardwired). I'll make sure the proper voltage is selected.

I'll also try connecting only the known good dimmer and see if there are any issues. I may even readdress it to 5-8 to see if the problem occurs on on the good pack. I'll also do the reverse to the "bad" pack. Either way, I'll try every possible combination and see what happens. Hopefully the problem does not reside in the board.

 

[JD]

Don't know about the loading. I've put 7 watt bulbs in cheep Optima dimmers and had them work fine. Most packs do want to see at least 50 watts of load. (Worth a try though.) Most of the time, DMX problems you described are caused because the pack is not getting a good read on the signal. DMX is asynchronous, so without a clock signal, the pack must be in step (frequency wise) with the controller. If you can sub a known good board and the problem remains, then you have a pack problem. If the pack works well with another board, then the output on the EDI may be slightly low or off frequency. It may be that both the pack and the board are both a little off and the combo stretches the limit. Of course, you have to first eliminate potential noise problems. Run one known good cable from the board to the one pack with a proper terminator and nothing else connected. If that works fine, then you have a noise problem. "Signal to Noise" problems can be tricky in their own right as both high noise or low signal will cause the same problem.

 

[church]

try the flickering dimmer on its own with a short cable and see if it still flickers. If not increase the cable length if it starts to flicker as you increase the cable length then the problem is most likely that either the negative or positive input of the DMX input has a problem. This can be as simple as a broken wire or a damaged input in the receiver chip. You can eliminate the cable by swapping it out to see if the problem goes away. Because the DMX is a differential signal it is possible for one input signal to be missing and it still work over a short distance i.e. a few feet and then become erratic.

Been there done that and got the T shirt for that problem.

Good Luck

 

[Les]

Thanks for all the suggestions. I finally have some time today so I'll try out some of the things you all have mentioned.

I feel like it's the pack because I connected it directly to the board with a known good cable and it had the same problem, while the other pack didn't have this problem at all. I'm going to do a little more switching around to try and confirm this. I'm hoping to remove the console as the potential problem because I already have some work to do to it and so far it's mostly cosmetic (other than replacing a submaster potentiometer). I don't really want to have to pay for troubleshooting a DMX problem and having it repaired. The packs on the other hand were given to me, so they're not much of an investment.

Still though, the flickering pack works well enough otherwise and seems like a good build quality. Definitely good enough to invest in a repair and use as a backup pack if I need to. Luckily they are true 600w per channel, at 2400w max rather than 1800w, so I could run 4 575w ellipsoidals and in theory be on the safe side. I opened one up and the chokes are completely potted and sealed. I've never seen one like that before. Seems like a good idea to me because it keeps the dust off them.

 

[Al D]

I know this is a few years late in coming, but I just repaired an issue with an Optima DMX pro 4ch dimmer pack. When dimmed it would blink at full for a split second on all channels at random times. I could not find a schematic for this dimmer (most certainly a cheap Chinese unit), so I was left to make guesses at what the problem was. I first tried the pack in stand alone mode, dimmed, and it worked perfectly fine. When I used DMX signal the problem was there. I tried changing the speed function output on my controller, different DMX addresses, terminating the signal, ( since I was using a 3' cable and it was the only thing in line, this was a last ditch effort).
I came to the conclusion that it was a DMX Driver chip. I had an old board out of another unit, so I swapped driver chips...to no avail. I also swapped out a couple 8 pin IC's that provide sub functions of DMX addressing, also to no avail. The next thing I did was pull out the trusty Blue ESR meter and start checking caps. I found one ceramic disc capacitor a 472 (4700 pico farads) that was bad. It was connected across the collector and emitter of a NPN BJT Transistor by the display. I did not have a replacement for it so I removed it and tested the unit and it behaved fine. The only thing different I noticed was the dimmer pack will no longer remember the DMX address that was entered. I am gonna order one and replace it, but that fixed my issue. I hope this helps someone.

 

[Les]

I hope this helps someone.

I ended up giving these packs away a few years ago, but thank you for posting your observations. It's always good to keep threads from dead-ending. I never resolved the issue with my packs, but it was mostly because I didn't have an immediate need and I lost interest. I had always assumed it was a driver chip but now that I know a bit more about electronics, your capacitor diagnosis makes a lot of sense. I am still in touch with the current owner, so I will pass that info along. Heck I might even buy them back if he's no longer using them.

Anyway -- thanks for posting and welcome to CB!

 

[JD]

Sometimes, when multiple channels on the same pack flash on, and DMX is eliminated as the cause, The problem may lie in the zero-cross detector. These can be thrown by noise on the AC line (sometimes by the pack itself), poor design, or even a weak or filtered power source, and of course any combination of the above. If the detector glitches, it throws off the ramp (analog) or countdown clock (digital) and the triac/SSR is gated at the wrong time, thus the flash. When this happens, all channels running off that cross detector will do the same thing. On three-phase, a third of the channels will do it. On shoebox dimmers (single phase) all channels will do it.
Interestingly, the worst thing you can do is plug it into a line conditioner! Although the conditioner will reduce line noise, it will also exaggerate the noise the pack produces and sees itself. (Kind of like the problem with running a dimmer of a transformer that has a built in triplen harmonic filter.)