Dimmer Pulsation

[James Remo]

Last saw it on a Siyan rack, patch round was the only solution at the time

[Don Allen]

Although this post on the LSC Technical Support Forum LSC E24 flashing is about a different dimmer, the neutral comments may be relevant

 

"The fact that the problem only occurs at one venue, which just happens to be a large hotel, is not too surprising.

 

The problem you are seeing is caused by a noisy (aka soft) neutral and/or bad earth connections. The function rooms in large hotels, particularly older ones, tend to have undersized neutrals with long distances involved, which can cause hideous distortion on the mains waveform.

 

The e24 has some complex software and hardware inside to cope with this, but the original software version was not able to work with very bad mains noise. Over the last few years we have seen 2-3 venues with a similar problem and on-site testing has allowed us to re-write the software for improved performance. So please update the software when you get a chance and let us know the results."

[dfive]

The A4k racks used to have this problem which was caused by a higher than normal resistance/undersized neutral, quite often you'd get if you were running on generators. I've seen it on A2ks fairly often as well, often in a way that's not reproducible in the shop. Some venues seem to be more susceptible to it, I've taken the same rig with the same racks to another venue and had no problems.

 

I've got around it in the past by softpatching around it, though quite why only some channels are affected is beyond me, or putting the dimmers on their own supply, not always practicable though.

 

Anyone got an answer on the science behind this?

[timsabre]

Bad neutral can make it difficult for the software to accurately detect the zero crossing point of the mains. So the triac /thyristor can get triggered at the wrong point of the cycle.

 

I can't think why some channels are affected and not others though.

[dfive]

Yeah, the certain channels bit is baffling my brain slightly. Figured it was down to zero cross, but discarded that thought when it wasn't every channel.

 

Glad someone thought along the same lines as me! Tolerences in components maybe?

[ed_ld]

I used to repair lots of these with the same fault when working at a certain hire company. From memory, there's a zero cross capacitor (40 nF possibly??) on each channel on the main bay trigger board on each dimmer module.

 

Easiest way to tell was that older modules had grey capacitors which tended to fail and then split open/develop a visual bulge when particularly bad. These caused a low level flicker at around 15% on the channel in question, normally when the rack was up to temperature. As soon as this was realised, Avos upgraded to a better capacitor and these are all light blue as opposed to grey. If we found a flickery channel on a module, we would simply replace all the caps on the entire board to be safe.

 

I know it's not an exact science going off the colour to tell which caps you have but it's been a pretty consistent way of telling over the years so far!