Avo FD rack dimmer playing up...

[pscandrett]

Hi

 

We have an Avo FD 48 way touring dimmer rack that's seen a lot of service (its history before us was Wigwam and then, I believe, previously Lite Alt where I suspect it got a lot more use than it does now!). It's made up of 4 x 12 channel dimmers.

 

On Friday night at a gig we noticed some slightly odd behaviour which I put down to induction somewhere along the line. At the gig I eliminated soca induction (from the soca loom itself); today I've had a chance to play in the warehouse with patching and different dimmers and have managed to narrow it down to the first dimmer playing up. The easiest way to illustrate the issue is to describe the symptoms we observed on Friday and today.

 

The patching for this first dimmer was as follows - simplified a little:

Channels 1-10 : 1 CP62 1kW parcan each

channels 11 + 12: 1 4 way molefay blinder each

 

I noticed the issue when programming... basically, if I put a lot of the parcans on at the same time, the blinders gently glowed. A few parcans, a slight glow - most of them, and a significant glow (as much as 30-40% I'd say), without any command to turn the moles on. Operation of the gig wasn't a problem because I didn't have all of them up at the same time and it wasn't the sort of gig where a glow was noticed anyway.

 

I've experimented and it's not unique to channels 11/12 - there is some sort of inductance/leakage across the channels on the first dimmer in general, and it's just that it's more noticeable with the blinders from FOH that I spotted it! As I say, the other dimmers are fine and behave as you'd expect.

 

Is it likely to be just that the first dimmer is old and knackered? I'm concious that the first dimmer is going to be the one that's going to have been used the most since people naturally start at the top and work down!

 

I've taken the top off the dimmer itself and there's nothing noticeably wrong with anything inside - although I'm competent with electrics I don't have much dimmer/electronics expertise, so I don't know if it's the control circuitry playing up or something more fundamental with some cores inducing a current in the other circuits.

 

I haven't yet asked Avo (although I'm sure they're nice people and will approach them! :-) for what it's worth - I just thought I'd ask for general background/opinions first. I don't think it's 'unsafe' per se, but without knowing what's causing the problem I can't be certain of what the risks are. If it's not a general problem then I'm tempted just to swap dimmer 1 and dimmer 4 in the rack and continue using them...

 

Has anyone any advice please? Many thanks in advance.

 

PS This might be more appropriate in Electrical and Power... sorry if so.

[Jonny DMX]

It sounds like the control card needs trimming/replacing. It is reletively easy to trim, although you will need two multi meters. One multimeter will need to measure the output voltage under load and you will need to bodge a patch lead to connect your meter to it safely. (from memory you're looking for 32V output when DMX is 30, and 230V when DMX is 230. I understand this is the best match for a linear curve on an FD rack) The other meter will need to have small probes and measure the voltage on the control card. (it should be 5V) you will also need a way to produce exact DMX values. If you speak to the guys at Avo I'm sure they'll talk you through it properly and tell you what values to look for.

 

This is where I would start, if that still fails you may need to repace the card and/or other components.

 

I hope that helps.

 

p.s. This is mains voltage stuff so if you're not sure about it don't try it. Don't sue me! :P

[Stewart Newlands]

Has anyone any advice please? Many thanks in advance.

 

PS This might be more appropriate in Electrical and Power... sorry if so.

 

could just be age and heat affecting a component like a resister or diode

[danjshelton]

Sounds like (as Jonny said) it could do with Trimming (especially if it's had a hard life in the past! (not that the past owners didn't look after it!)). Avo have a handy online guide to trimming! (Link) Quite comprehensive and the full details are there! Try this and then let us know how you get on.

 

If that still doesn't work then I would suggest ringing the Avo service department, there a friendly bunch (I should know I used to work there!).

 

Cheers

 

Dan

 

PS Usual stuff applies, don't mess with electrcitiy if you don't know what your doing!

[pscandrett]

Sounds like (as Jonny said) it could do with Trimming (especially if it's had a hard life in the past! (not that the past owners didn't look after it!)). Avo have a handy online guide to trimming! (Link)

Many thanks for the advice and link, and to the others too. It looks like it would be good to do this anyway, and I'm confident doing it - but I'm not sure how (AIUI) effectively recalibrating the dimmer curve will fix one channel being affected by another. Am I missing something?

[maeterlinck]

Did you read to the end of the Avo trimming link? There's some unrelated fault finding suggestions that might be of use to you.

 

That said Avo know their kit very well and a quick phone call to them could well sort your problem quick sharp.

[pscandrett]

That said Avo know their kit very well and a quick phone call to them could well sort your problem quick sharp.

Thanks, have called them and we're investigating (it doesn't appear to be the control card in the dimmer either, unfortunately). I'll try to update the thread when I know more/what the problem was.

 

Thanks to all who've helped thus far.