I have repaired many dimmers of the same type. The problem is most surely the
Triac (two SCRs back to back in the same case.) If you have any experience in electronics, you can identify the triacs by the fact that they are in TO220 cases. That is a
flat transistor looking case with three leads and a
tab heat sink for mounting. Locate the AC
connector that is the errant
dimmer. follow the black
wire or if the color is not standard, the one coming from the brass screw and the smallest slot in the
connector front. Where that
wire goes into the
circuit board, the nearest of the Triacs to that
wire is probably your problem. In many cases it might require removing to whole
circuit board assembly to desolder the
triac. In the case of LIghtonics, the
triac is under the
circuit board and requires removing quite a
bit of circuitry to get to it. If the triacs are quite visible and can have the
heat sink screw removed, just cut the leads as close to the
triac as possible. Put the new
triac in exactly as the old one was mounted.
Lay the leads of the new one on the leads of the old one. You might have to
trim a little off the ends of the new leads for them to
lay smoothly on the old leads. Now just solder the leads together. This is the quick and dirty way to repair these guys. The fact that it might get blown again, it may not be worth doing a job where the old leads are removed from the board. That is a choice that you have to make based on the amount of time you have and your confidence
level in such activity. If you do decide to remove the old leads, don't try desoldering all three leads and pulling the
triac out intact. Cut the leads and remove them one at a time. This helps keep the amount of heat used in desoldering to a minimum and will help keep the
conductor laminations from being pulled up from the
circuit board.
Most of the
shoebox dimmers use a 12 or 16 amp
triac. You can get replacements in the 20 and 24 amp models on the same TO220 case. They will work just the same without any modifications to the circuitry, and will be much more robust in avoiding a failure in the future. WARNING!! Make sure that in purchasing the replacement
triac, that you get one that has the heatsink electrically isolated from all three leads, if not, you might see a lovely
smoke and light show when you
plug the
dimmer in.
I ususally use a BTA20-600CW
triac available from Mouser.com The BTA20 is the important part of the number. Considering the cost of the shipping and the low cost of the
triac, I usually
purchase from 10 to 20 at a time. In any case it seems silly to
purchase just one, when it is one of the most common electronic parts used in the
theatre. While you are ordering it, you might want to
purchase a few 75176 communication ICs. They are the tranceivers used to transmit and receive
DMX and there is one or more in almost everything that uses
DMX.
I hope this helps.
Tom Johnson
