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LD90 Faults


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We have (secondary school) two LD90 dimmer racks with two faulty channels (4 & 23) the manual suggests that the Power Devices (riacs) need changing, where can I get these (05 004 18 (79104) 2.5Kw power device 2 off) from. Strand Website is useless and I have not had a reply from their approved agents.


Also some time ago channels 1 to 12 swapped we now have


12-1 13-24 25-36 37-48


Anyone got any ideas???



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Hi David,


If you enter LD90 into the search box, It will bring up loads of previous threads regarding your problem.

I think the Triac (or whatever they been named) are available from Farnell or other good electronic suppliers.

Occasionally the opto-coupler and an associated resistor may need replacing.




John Mac.

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Farnell do stock them and were reasonably priced when I last bought them. The particular devices in question, TPDV840, are called 'Alternistors' - a trade mark for a special type of triac that works with well with highly inductive loads. Could you odd channel assignment simply be a repatch in the dimmer menu?


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The dimmer channels can be patched to DMX channels, so it's possible that the patching has got corrupted somehow. Can't remember how to do it (haven't used an LD90 for years) but it should be in the manual.


OK, Lucien hit "post" quicker than me!


I had more problems with LD90 than I've had with anything else. The power devices died for a passtime, and 10 years ago I couldn't find them anywhere but stage and they were EXPENSIVE. We had 2 racks, and the processor modules in both packed up twice (at £1k+ a shot as nobody would repair them). The second time we ripped the lot out and replaced with hardwired betapacks which were no problem for the 5 years until I left the venue and I'm told have been no problem since.


I don't know if the problems were caused by them being installed up in the roof (very hot and humid), by them being wired 2 phases to each rack (not quite sure why as we had 8 channels to a bar and the racks are 8 channels per phase so its not even a case of doing it to get 1 phase per bar), or by it being a bad design. All I know is I spent way too much time sat on top of the control room fixing them!

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Hi David.


Someone must have got really bored to repatch the first 12 dimmers in the rack.


Depending on what version of software you have fitted, you need to select patch then using +/- scroll down 'till you get to dimmer patch section. Cursor right (>) and work your way around the menu using +, -, >, < buttons. There is also a quick option (DMX START) which will patch all your dimmers in sequnce within a rack from a start number of your choice.


If things are still playing up having checked the rack patch, it may be an idea to check the patch on the desk (if it has one).


We still service quite a few LD90's and have component spares to maintain them.



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