Problem with this circuit board.

This circuit board is from a Show Tec Multidim Mk111
**broken link removed**

Its used to control disco lights going on and off.

When i power on the unit all the lights should be off because there is no dmx signal going to each of the 4 channels.For some strange reason the second channel (the one highlighted in the image) stays turned on.

I think the black devices attached to the aluminum heat sink are PNP N devices. This is what is written on them BTA16 600B Mar 111B0

Is there any way of trouble shouting this board and can anyone tell me what could be a possible cause.

The BTA16 is a TRIAC. The simplest approach would be to just replace it. Without a schematic it's impossible to offer any other advice other than to say look at the signal on the triac gate with a scope to see if that looks right.

I can't download the picture, it's too big for my slow internet connection but from what you describe, it uses the BTA16 in series with the power line to act as a switch and turn the lights on. The BTA16 600B is a 16A triac, not a transistor. For some reason one of them is conducting all the time, the most likely cause is the BTA16 600B has gone short circuit but you may also have an interference supressor connected across it which has shorted as well. I'm guessing the four white ICs are opto-couplers and while it isn't impossible that something before them (to the left of them in the picture) has gone wrong, the chances are the fault is on the AC side (right) of the board.

If you have a test meter, while disconnected from the mains, measure the resistance across the first and middle pins (with the component upright and the part number facing you), it should be very high value, at least 100K. If it's lower, try replacing the BTA16 600B. Make sure you get one with the same part number because the BTA16 is a family name and is made with different numbers and end letters.

Brian.