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intermitent issue with a fat frog

lamps galore

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Hello all, long time no see (or read for that matter...)


I was hoping one of you could shed some light on the following problem.

One of the venues I work for has a Zero 88 fat Frog. Over the last 6 years or so (since the venue was established and the desk bought from new) it has occasionally had a moment of random flashing that left the lighting ops slightly bemused and concerned. Since I started working for this venue (three years ago or so) the problem has occurred 4 times. The desk has been sent to a couple of hire/supply companies that have returned it without finding any cause, or anything untoward, but the problem ceased. At the third time, I thought I'd call Zero 88 as in the past (and present)I've always found them helpful. However, they have not been able to suggest anything that may cure the problem - an earthing issue was suggested, but after some investigating, couldn't find anything wrong on that front.

The desk basically does the following - after booting up it'll work fine - loads the memories/submasters fine, show runs without any problem. A day later, it'll start just fine as it should, but a channel will suddenly flash without any input from the lighting op. This same channel will then flash a couple more times, and then go off - all this independently of whether said channel was programmed into the live memory or not. It'll then start again 3 or 4 minutes later, and possibly joined by another two or three channels. The desk will then behave and the issue will not happen for another 6 months.

Earlier today it decided to flash up to 15 diferent channels all at the same time. I wiggled the DMX input and the same channels then flickered on and off...

If anyone has any ideas I would be utterly greatful to hear from you!



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I'm just waiting for a DMX tester to arrive (ordered a couple of days ago) to test the DMX cables the venue has. Do you know what would be the best way to test the DMX installation itself?


I did several tests over the summer (july and august) where I swopped cables on the DMX switcher (from desk to switcher and vice versa, from other items like movers, with and without movers, from different DMX points around the auditorium and control room...), but I've not actually tested the cables themselves as I didn't have a testing unit or the installation itself as I don't know how to...

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Also make sure that your DMX line is terminated correctly at the end, either by a terminating switch in the last dimmer or a termination plug in the last loop out. And check that ONLY the last dimmer is switched to terminate if it's a switch on the dimmers. If you find it's not terminated and everything stops working when you do terminate it then there may be a wiring issue like a broken connection.


I know there are a lot of self styled experts out there who think that termination is not needed and some who even think it causes problems. But the simple fact is that it is an important part of an RS485 (DMX) network and if they had a problem with a network when terminated, they should have looked for the actual fault instead of removing the termination to "fix" it.

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