Weekend project - Chinese kaleidoscope light

[Bud]

Back to Christmas time a month ago I bought a pack of two chinese Christmas kaleidoscope lights. They have a small slow rotation motor with a bubbled clear plastic wheel on the shaft and an aluminum PCB behind it with 3 high power LEDs (RGB) shooting through the wheel. Then the light go through the clear faceted spherical cover and creates a moving RGB pattern on the surface you project it to.



The Red LED on both lights soon failed. One right after I unpacked the light and turned it on, the second one failed in 3 nights. This was a quick weekend evening project to fix them.

The lights have a small constant current driver board inside with a 5W LED driver chip CL1221. The circuit is very simple and the load current is set by the resistor on pin 1:



The resistor value can be calculated from the formulas in the datasheet. The datasheet is in Chinese but I at some point found the English version but did not keep the link. Anyways, you basically just need the reference schematic and the formulas. The chip has two 4.7 Ohm resistors connected in parallel and connected to pin 1. That sets approximately 275mA load current (I figured the Np/Ns ratio of the transformer windings is ~5.2). The green and blue LEDs work OK with this current but the red LEDs failed.

The 3 LEDs are mounted on an aluminum board. To get access to the board I removed the wheel and a retaining washer that held it to the motor shaft. It was the LED1 that failed, I unsoldered it.



I ordered a more beefy red LED from Digikey (350mA max current)



It is a bit larger than the failed one but fits the PCB pads just fine.



Soldered on the PCB, watching the proper polarity. The three LEDs are all connected in series. I also put a bit of thermal paste on the LED bottom.



That did the trick and the lights are now ready for the next Christmas season.

[floobydust]

Those 1W and 3W bead LED's need the thermal-pad soldered to the MCORE pc board, for heatsinking.
I notice originally there was no paste, the factory just hand-soldered the leads down but no solder for the thermal pad? I would expect them to overheat and have a short life.
I find it takes a ton of hot air to heat up MCORE enough to solder/desolder these LEDs.

[Bud]

The  bottom pad on the original LEDs was not soldered to the board but there was some sort of thin plasticy gasket between the board and the LED which i replaced with thermal paste. The failure mode however seemed  to have something with overcurrent i believe, as one of the lights quit right when i brought itfrom the store and swithed on for the first time. The other one was outside in winter,  i guess cold weather naturally helped with cooling. Likely the red LEDs were 200mA or 250mA ones andthe driver was pushing 275mA. Will find out next Christmas