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DMX light problem


djbzentertainment

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Hi all am new to this forum and got to find out about when doing a search for some info on my LA Bomba disco light. The light is quite old and has been working fine but has started to blow its internal 250v 5a glass fuse, seconds after the unit has been turned on. The fuse goes with a proper bang as well! An hour ago I tried a new fuse and it literally blew it to bits,glass and all. Not being an electronics wizard I decided enough was enough and try and find some help! After having the case open I did notice the fuse holder was loose, and attached to the fuseholder is a strange looking thing which I can confirm is an anti overheat transistor (forgive my terminology!) Because the fuse holder was loose (the locknut was loose and allowing it to turn) the transistor thing was touching the metal casing of the light. Now I dont know if this is a problem or not but I thought it worth mentioning. To describe the light, it consists of a top stepper motor turning a multi faceted mirror back and forth and a lower stepper motor turning a gobo wheel back and forth. The bulb is a 24v 250w elc. So, the question is, does it sound like an easy repair or is it bound for the bin? Many thanks in advance!

 

Bob

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Exploding, er, non passive failure of the fuse means dead short.

 

There is no anti overheat transistor, do you mean a bi metal overtemp switch like:

 

http://www.comstatinc.com/images/thermo.jpg

 

If anything is shorting to the case sounds likely its the cause of your problems, if the unit is old time to look at the insulation on internal wiring for signs of weakening as well.

 

If your sure all the wiring is intact and safe with no shorts and it still blows fuses could be primary of trafo or the switch mode PSU, depending on age, giving up, then its only value would be sentimental...

 

HTH

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Exploding, er, non passive failure of the fuse means dead short. There is no anti overheat transistor, do you mean a bi metal overtemp switch like:http://www.comstatinc.com/images/thermo.jpgIf anything is shorting to the case sounds likely its the cause of your problems, if the unit is old time to look at the insulation on internal wiring for signs of weakening as well.If your sure all the wiring is intact and safe with no shorts and it still blows fuses could be primary of trafo or the switch mode PSU, depending on age, giving up, then its only value would be sentimental...HTH
Exploding, er, non passive failure of the fuse means dead short. There is no anti overheat transistor, do you mean a bi metal overtemp switch like:http://www.comstatinc.com/images/thermo.jpgIf anything is shorting to the case sounds likely its the cause of your problems, if the unit is old time to look at the insulation on internal wiring for signs of weakening as well.If your sure all the wiring is intact and safe with no shorts and it still blows fuses could be primary of trafo or the switch mode PSU, depending on age, giving up, then its only value would be sentimental...HTH
Thanks everyone! Err, yes the overtemp switch thing looks very similar to the photo. Mines brown with a metal ring round the top of it and its soldered to the fuse holder (which is plastic). I have checked as best as I can for any dodgy wiring and all seems fine. If thats the cause of the fault then all I can say is what a rubbish design it is. What has happened then, is that I have replaced the fuse, which requires a pushing down and twisting action, the fuse holder locknut has been loose, the fuse holder has spun and stopped when the overtemp switch has contacted the metal case, then at switch on, dead short and BOOM! Ok, if that cures the problem, should I wrap some insulating tape around the overtemp switch to stop it happening again? Once again thanks everybody!Bob
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should I wrap some insulating tape around the overtemp switch to stop it happening again? Once again thanks everybody!Bob

 

Insulating tape tends to dry up and fall off, de-solder and use heatshrink boots on everything or self-amalgamating tape at a pinch:

 

http://www.tlc-direct.co.uk/Main_Index/Cab...s_Index/Tape_A/

 

 

 

 

 

Thank you to all who replied to my post. Stripped the light right down and properly checked for damaged cables, gave it a really good clean, fully tightened the fuseholder lock nut and repositioned the offending item and hey presto, it works! I would never have realised that it was shorting, the inside of the housing is painted and there were no signs of an obvious short, (I.e discolouration on the housing.) Having said that the 240v power gets dropped to 24v via a transformer so there wouldnt have been much of a spark anyway I suppose.

 

Thank you very much all and you can be sure I will be back with more ridiculuous questions in time!!!

 

 

Bob

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