Control/Dimming I need help fixing an old dimmer

[cchauche]

Ill give some background info. on how the dimmer broke in case it might help.

I was ringing out the system in a theater I just started working in. (It was my first show there) and when I tested dimmer 31 there was a spark and the light didn't turn on. I quickly figured out the problem had been a loose wire in the connector created a short. So I fix the light, then find the circuit breaker for the dimmer and flip it back on. Much to my surprise the light turns on. I go and clear out the board but the light remains on. So I now have a dimmer that will not turn off, it is at full 100% of the time.

Usually I would just call the local theater supply place and have them fix it but they will not touch our dimmer rack because it was a custom install.

So now I need to figure out how to fix it.

I'm told that often when the SCR fails the dimmer will stay on at full like my dimmer is doing. Unfortunately I know nothing about SCRs except they are used in most dimmers. So knowing nothing I took the dimmer apart and I've found what I think is the SCR but I dont know how to test if its good. Second I can't really find any inoformation on the part. (Part says TAG T4012DK 9249)

So if anyone knows how to test an SCR or might know better how to fix this please let me know. I could really use this dimmer.

(Some pictures bellow)

 

[PeteEngel]

Best thing to do is contact Cypress Creek. Cypress Creek Dimmers They can probably hep you out. PS, a good cleaning wouldn't hurt either... i think i see a cat in there!

 

[mrb]

thats a 40 amp triac. There is a NTE cross for it http://www.nteinc.com/specs/5600to5699/pdf/nte5679.pdf those usually fail on (either 1/2 or full brightness depending on if one or both SCRs inside went) just replace it and you should be good to go.

 

[JD]

Looks more like a BTA-40

BTA40-600B STMicroelectronics Triacs

Spec sheet-

http://www.st.com/stonline/books/pdf/docs/7469.pdf

Mouser.com has over 300 in stock. About $8 plus shipping.

 

[derekleffew]

... and when I tested dimmer 31 there was a spark and the light didn't turn on. I quickly figured out the problem had been a loose wire in the connector created a short. So I fix the light, then find the circuit breaker for the dimmer and flip it back on. Much to my surprise the light turns on. ...

It might be noted that triac s are particularly susceptible to a short circuit. The triac fails before the breaker has time to trip. One of many reasons why higher-quality dimmers use SSR s.

Working with electricity is dangerous. When in doubt, consult a qualified professional in person.

 

[JD]

Triacs are a bit more susceptible to damage from a short as everything is done in one multi-layer junction. (see below) Dimmers that use SCRs at least have their heat load spread out between two devices. Even SSRs (solid state relays) usually contain two SCRs, although there are a few SSRs that actually contain Triacs.

Because of the need to dump heat real fast on a short, the SCR combos do a little better. Because of the fact that shorts happen in stage lighting, better dimmers almost always use SCRs or SCR based SSRs.

 

[cchauche]

Thanks for the help!