Film-Tech Forum ARCHIVE: Kelmar Showcase Dimmer not dimming

This is topic Kelmar Showcase Dimmer not dimming in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Stephen Frazza (Member # 2320) on 08-31-2011, 12:17 AM:

My Kelmar Showcase Dimmer is not dimming the stage lights.

You get full voltage on both settings high and low for the stage lights and the top part of the dimmer ,the house lights, works fine.

I tried a new triac but the same thing happens. I messed with the pots inside also and still no luck.

Besides a new triac , what other part inside might have gone bad?

Also another question - Does it matter how the triac is connected. When I tried the new triac I matched it up to the way the old one was wired. But it seems like it isn't right when I compare it to another one of our working dimmers.
I also tried rewiring the triac to what I thought was correct and that didn't work either.

And I thought I remembered in the past when a triac goes usually the lights don't work at all. This time they are stuck in fully on position.Am I remembering correctly?

Thanks

Posted by Gordon McLeod (Member # 33) on 08-31-2011, 10:01 AM:

Several possibilities
The opto coupler (usually MOC3011) or the two resistors in the snubber beside it usually around 150 ohm and 680 ohm
The triac does have polatiry issues
There are three terminals the one with the small tab is always the gate (small wire)
The other two are MT1 and MT2 and if reversed the triac will either not fire or flicker
If you have a scope it would be the best to check if there is a square wave of varying width as the dimmer fades on pin1 of the opto

Posted by Louis Bornwasser (Member # 3063) on 08-31-2011, 03:40 PM:

Wire it exactly like the other one that works. Swap the door and see if you have a circuitry problem. Yes, Kelmar repairs these. Louis

Posted by Stephen Frazza (Member # 2320) on 08-31-2011, 07:00 PM:

I found another spare triac we had and that had a wiring diagram in it. Once I wired it correctly it worked no problem.

Thanks for the replies.