deskkky Posted May 4, 2012 Share Posted May 4, 2012 Hi, we have a few of the 36x3w tri led par cans, one of them has developed a fault where the colour blue its permanently on from powering up, even if no DMX input is present. I have changed the adress, put it music mode but blue will not go off. Apart from that it works fine. No obviuse damage to circuit boards & its out of warrenty. Any ideas? Thanks Link to comment Share on other sites More sharing options...
dbuckley Posted May 4, 2012 Share Posted May 4, 2012 Wild guess - mosfet gone short circuit? Link to comment Share on other sites More sharing options...
Brian Posted May 4, 2012 Share Posted May 4, 2012 Any ideas? It's broken. Been there, done that. Luckily mine was still in warranty (got to love the 3 year warranty from Thomann). These higher power units are very different to the old type of LED can. The old style was a simple 50Hz transformer making DC which was then pwm'd with a fet or transistor to drive the LEDs. The new style use one or more SMPSUs so lots more to break. The failure on mine was down to the nut from the back of the DMX socket coming loose and falling onto the PCB where it fried something. And the same fault happened to a friend as well so it's not a one-off. Link to comment Share on other sites More sharing options...
deskkky Posted May 4, 2012 Author Share Posted May 4, 2012 All well, thanks anyway! Link to comment Share on other sites More sharing options...
Nicktaylor Posted May 4, 2012 Share Posted May 4, 2012 All well, thanks anyway!All well or Ah well? If fixed what was it? Link to comment Share on other sites More sharing options...
deskkky Posted May 5, 2012 Author Share Posted May 5, 2012 All well, thanks anyway!All well or Ah well? If fixed what was it? Sorry, Ah well. Still broke, ordered a new one! Link to comment Share on other sites More sharing options...
dbuckley Posted May 6, 2012 Share Posted May 6, 2012 So did you check the outpur mosfets? Two minute job with any old multimeter once you're inside. It really is the most likely fault. Link to comment Share on other sites More sharing options...
deskkky Posted May 6, 2012 Author Share Posted May 6, 2012 So did you check the outpur mosfets? Two minute job with any old multimeter once you're inside. It really is the most likely fault. I havn't no, I would like to try though, but not sure what I would check, cont against them and -?Thanks Link to comment Share on other sites More sharing options...
dbuckley Posted May 6, 2012 Share Posted May 6, 2012 Below is a (unfortunately, blurry) pic of the inside of a LED parcan. The red box indicates one of the mosfets, of which there are three (though this parrticular board allows for four for RGBY use, the fourth not being fitted), and the yellow boxes indicate the important connectors, the left being the feed to the LEDs, the right being the power supply. The LEDs are connected so that their positive (+ve) sides go to the +ve of the power supply, and the mosfets switch the -ve side, this is called low side switching. The microprocessor on the board switches the mosfets on and off many times a second, and the ratio of on to off determines the brilliance of the LEDs. So, one leg of the mosfet goes to -ve, another to the LED chain, and the third is the control pin that is connected to the microprocessor. To find out whats wrong, set your multimeter to measure ohms, using the lowest range it has. Place one probe on the-ve powe supply connector. Place the other probe on each of the pins of each mosfet in turn. One pin of each mosfet will always read close to zero ohms, as its connected to the -ve supply. The others should be many (if not infinite) ohms. If one mosfet has close to zero on two pins, then there is the shorted mosfet. Having said that, the next challenge is to get the busted mosfet out... http://davidbuckley.name/pix/led_pcb_marked_up.jpg Link to comment Share on other sites More sharing options...
timsabre Posted May 6, 2012 Share Posted May 6, 2012 Having said that, the next challenge is to get the busted mosfet out... Judicious use of a hot air gun (paint stripper type) will get it off for you, you will see the solder melt, then whip it off quick with some tweezers.Be careful not to dislodge any other components while the solder is melted and keep the board horizontal. I fixed quite a few things this way before buying a proper hot air rework station. Link to comment Share on other sites More sharing options...
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