Stairway Recessed Indoor Lighting Repair- Randy LED 1.5W White-Ledkia
One of the 7 recessed indoor stairway lightings in my nephew’s home no longer worked. And my brother asked to see what may have happened to the circuit. My nephew brought it with him after he had removed it from his stairs for further investigation. These led lights in his home were also automatically activated by remote proximity sensors.
It was a white Randy model from this online link: https://www.ledkia.com/nl/kopen-led-inbouwarmatuur/466-randy-led-trapverlichting-met-grijze-finish.html
According to the specifications on that website these lights are guaranteed to work for at least 40.000 hours which is everything but true because these brandnew lights were installed only a few months ago and already one of them no longer works!
One side of the small board (marked JM-3902) with the brown phase and blue null 230VAC input wires is shown above with the 2.2uF 400V DC e-cap and L1 coil.
On the other side of this board eight warm white 3V leds in series are soldered. And also an ES12 diode, another small capacitor, R1 with code 120 (12 ohm) and a bridge rectifier BD1 marking MB10F, plus a unknown soic-7 smd chip with marking 77SKL0D1JC.
And clearly only one of the eight 3V leds showed a black spot on its yellow top. And this led now measured being a burned open connection.
Why now obviously none of the leds in this Randy model lighting worked anymore.
Notice the second yellow led with black spot on the right in above photo. None of the other components showed any burn marks and also bridge rectifier, diode D1, L1 , R1, C1 and C2 measured fine. The only question now was if also ic U1 was still okay since no datasheet or any other information could be found on this chip.
This chip no doubt controlled the voltage and current that goes through the leds in this circuit. In next photo the – and + voltage sides on all 8 leds are marked with a red marker. We first checked all leds individually with our WanPtek power supply set at 3V and indeed saw that all leds were okay except the led with the black burn mark on top.
After the defect led was replaced with another Samsung 3V led the series circuit of leds was tested with the WanpTek 30V 6A adjustable power supply set on to 23.9V and at a maximum current of about 30mA. And now all 8 leds worked showing a very bright light!
The Samsung led that was used here to replace the defect led probably was a 2828 or 3228 led type 1.5-3W with built-in zener diode. Because we didn’t have the exact same original led. And this replacement led had very small leads which maked soldering less problematic. The original defect led however was easily and quickly desoldered with my old trusted Gordak 952-A hot-air station.
The only thing left to do was checking if the unknown controller chip was still okay without blowing up the entire circuit by just connecting it unsafely directly onto the dangerous 230VAC powerline. So like explained in a previous article I used my great Led backlight tester that outputs up to 322V DC safely and connected it to the 230V AC phase and null wires of the stairway indoor lighting circuit.
Next photos show the circuit under test safely powered by my led backlight tester.
And to make sure that also the voltage over the 8 leds was correct and not higher than about 24V DC (8 x 3V) that voltage was also measured. Which also will reveal if our unknown controller soic-7 ic is still okay outputting the correct maximum voltage of about 24V DC.
Above shows how the output of unknown ic U1 was measured. (- and + on all 8 leds in series).
After measuring 22,7V DC we knew that ic U1 was still okay and it confirmed that the circuit worked splendidly. After this we also double checked the circuit with a lightbulb in series on the Stairway lighting circuit directly connected to 230V AC power line.
The light bulb never glowed. So the circuit was indeed completely fixed and again at little cost.
Below the quick handdrawn circuit of this small board.
Although the only culprit here was one of the 3V leds, the question here remains why a brand new lighting went out of order when 40.000
hours of operating time were promised. And if the 6 other identical stairway indoor lights of my nephew will fail soon too, or will keep on working?
Albert van Bemmelen, Weert, The Netherlands
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