Dimmer timing issue?

Joined
Apr 7, 2014
I'm running a 16-channel distributed dimming system for a show, with an NSI MC-7516 control board, and I'm having trouble with my dimmer box for channels 5-8. I'm doing a general wash with 13 of my 14 instruments and have it set to a sub. When I've been bringing it up or down, channels 5-8 have been coming in before any of the others; at 20 percenton the board, these four are much higher than anything else in the system, more like 40 or 50 percent. I thought it might have been a dimmer issue, since the pack I have at that point in the chain is a DP-DMX-20L and I've had some trouble with this one and it's twin. But when I switched it for a DP-DMX-4B, the issue persisted. I've worked with this equipment for two years at this point, and thanks to us being a low-budget professional that barely qualifies for it on a financial level, this has all been donated and I don't know the history of these pieces before I came in. Any possible solutions to this? I also do lack a terminator plug, but I can't imagine there's much noise since there's less than 150 feet of cable altogether.
 

JD

Well-Known Member
Joined
Jan 1, 2005
Location
North Wales PA
Just paging through the manuals for the board and the packs. I don't see any settings for the dimmer curve. Some dimmers allow you to use one of many different curves and that almost sounds like what you are dealing with. So, we need to narrow things down. If pack #1 is set for address 001 and pack number two is set for address 005 and the two act differently, first try reversing the addresses on the two packs. Does the problem stay with the pack, or stay with the same channel numbers?
If it stays with the same channel numbers, then a full memory clear on the board may be in order. (factory default.) Even if the board doesn't have the feature, it may still be in the software and held in a memory registry.
If it stays with the pack, then there may be a problem with the ramp generator in the pack(s) or it may be designed using a different dimmer curve.
 
Joined
Apr 7, 2014
It stayed with the pack, but the issue remained even with a replacement pack. I'll try another to see if it solves the issue, but I haven't had this problem with any of them before. The 20L has a buzz going when I bring up any of its channels, so it may be developing an issue (its twin is fried, but had the same sound when in use, so this one could be on its last legs).
 

Harley Morgan

Member
Joined
Mar 17, 2014
Location
Bloomington, IL
Actually I believe there are two coils in those packs. I have 13 of them but it's been a while since I've been inside of one. The most common problem I've had with them is the triac failing. None of mine buzz so this is probably a different issue entirely.

I suspect that you have a power or cabling issue, since you had the same issue with two packs, as well as swapped addressing.

Sent from my HTCONE using Tapatalk
 

kicknargel

Well-Known Member
Joined
Aug 10, 2009
Location
Denver, CO
It stayed with the pack, but the issue remained even with a replacement pack.
Aren't these contradictory findings? If the problem persists on a replacement pack, either the problem is unrelated to the pack (and is in the console or power/control) or you have two packs with the same problem. If you put the problem pack in the place of a known good pack, will it misbehave in that location? If you put a known good pack in the problem location will the problem persist?
 

JD

Well-Known Member
Joined
Jan 1, 2005
Location
North Wales PA
If a certain make/model of a dimmer pack works differently than another make/model of dimmer pack, there may be nothing wrong with either pack!
In the design process, the designer must decide what dimmer curve the pack should run. More expensive dimmers actually let the user decide. One would think the output of the dimmer would be proportionate to the level set on the board. This would be known as a "liner" curve. Unfortunately, lamps to not get brighter at a liner rate. Because of this, several non-liner curves are in use by dimmer manufacturers so that the light appears to be getting brighter at a liner rate. Well, guess what happens if two packs on the same system are designed with different curves? Exactly what you are seeing. set them both at 3 out of 10, and the lamps connected to the packs are at totally different brightnesses!
Now, I can't rule out the idea that you have multiple models of the same dimmer that have failed in the same way, but I did want to bring to the discussion the concept that the packs may simply have different curves by design.

PS: I can add that I have serviced DP-DMX-20L packs and they are pretty well built for a "shoebox" and do contain 4 independent chokes of reasonable size.
 
Joined
Apr 7, 2014
Alright, after some further work, I'm thinking it's a cabling issue. I also discovered some of my wall circuits have died, which means I was wrong when I thought my other 20L was fried. Turns out it works, even if it's memory seems iffy (it sets itself back to starting at channel 17 in the two-channel setting whenever it's turned back on) but it no longer buzzes, at least. This is the third pack I've put in that place in the chain and changing the address doesn't solve it. None of my equipment allows me to change liner curve, so I'd rule that out. I'm going to change out my cabling between the console and that dimmer and see if that solves it.

I suspect I'd have less issues if I wasn't working with old equipment that was all donated from about six different sources and never taken care of and has no record of maintenance for any of it beyond the two years I've spent cutting my teeth on it. I can't say how much I appreciate all the advice.
 

RonaldBeal

Well-Known Member
Joined
Jan 24, 2004
Location
TN
Do the lights responding differently have different lamps? Different filament lengths and thickness in a bulb can subtly change response times.
 

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