DragonX 4 Bar LED mobile DJ Stage Lighting Packages/Portable Par Can Kit Gig Spotlight Bar Set/ Sound Activated Wash Flex Light Party System
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| Cracking the lid |
I purchased this last year for my son's school to use in productions with good result. This year during practice, the light tree was knocked over after it had been on for an hour or so and when it hit the floor, two of the four light pods went out. What is this, an incandescent bulb? No, just some poor engineering.
After I found out about the accident, I brought the pods home and opened them up, six screws around the ring and three on the front plate (the center one can stay in as that holds the lenses into the support ring.
Inside the box is quite straightforward, there's a single layer flexible printed circuit board (FPC) bonded onto a 2mm aluminum plate, and 5 wires coming in from the light tree with a GND, +12v, and RGB signal wires. The circuit is three parallel PWM circuits for each of the RGB, you can see the power transistors and inductors quite easily.
In not too much time, I discovered the cause of the blackout, the LEDs had been dislodged from the respective traces on the FPC (LED1 for instance).
On looking at the LED package, it's quite hefty with a large metal back for heat sinking. I realized the FPC had holes cut underneath the LED to thermally bond to the aluminum plate for a heat-spreader. Then I discovered what had happened. With little to no heat-sink compound, the LED package had no place to dump heat other than through the leads, and being a thin FPC, there was not much copper in the traces to pull away the heat. After some period of operation, the LED package go hot enough to MELT THE SOLDER, and when it fell over, the weight of the lens package just above was enough to dislodge the LED in the crash.
I had some Arctic Silver 5 thermal compound around from a recent computer CPU replacement, so after a small dab of that, reset the LED and soldered it back in. If it came completely off, I found a quick check of the LED with a diode check meter was enough voltage/current to just light the RGB emitters inside and verify polarity/operation.
Once back together, I powered it up and found I was still missing blue on that lamp. Closer inspection of the circuit, I found an open between LED1 and LED2 on the FPC, so I soldered a wire jumper directly to the LED lead to fix the trace. I suspect the long high-temp operation may have dissolved the FPC copper trace into the solder bond and what looked like a reasonable re-solder joint was not.
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| Repaired DragonX light bar |
