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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Parasuraman S
January 14, 2023 at 10:57 am
A very detailed report on a professional and successful repair with a unique manuscript diagram! Many thanks for sharing!
Waleed Rishmawi
January 14, 2023 at 3:13 pm
great repair work. the only issue I have with such repair is when I try to solder off the bad LED's because it is mounted on a metal piece for cooling and when applying heat to take off the bad LEd it does not come off eaily without making marks on the board. thanks for sharing and have a blessed day
Albert van Bemmelen
January 14, 2023 at 5:49 pm
I know what you mean and have experienced that issue with other boards (especially those from Led lightbulbs). Removing the bad led on this stairway light with hot air however was very easy and done in only a few seconds.
Yogesh Panchal
January 14, 2023 at 4:44 pm
Good Job! Albert
Henrique J. G. Ulbrich
January 14, 2023 at 10:25 pm
Great job, Albert. Thanks for sharing.
In my case, I am in recent times dealing with LED lighting. The truth about LED lifetime is already known: the component itself (the LED) can have 40,000 hours lifetime according to its manufacturer, but this is only true if it works cool! During operation, the LED dissipates a considerable amount of heat, and a proper cooling system must be provided. In commercial products (most part chinese, of course), in order to lower production costs, the required aluminum area is not sufficient, leading to a lack of dissipation. To make things worse, the manufacturer also saves in thermal paste quantity, i.e., they put few thermal paste between the LED and the dissipation mass. With this, the heat generated by the LED is not transferred properly, causing the LED to work warmer than normal. Of course, in this condition the manufacturer's 40,000 hours lifetime is invalidated.
When I am dealing with these lighting products, I always (when possible) remove the LED, wipe off the old (and commonly insufficient and/or dry) thermal paste and put a new thermal paste, covering uniformly the LED and the aluminum surface. This can be considered a preventive maintenance and surelly improves lifetime.
Albert van Bemmelen
January 18, 2023 at 2:08 pm
Thanks for your valued info Henrique. Sadly there was no aluminium cooler nor any thermal paste applied to this ledkia indoor stairway led light. So hopefully the 6 other lights won't suffer from the same defect.
Mohamed Kikia
January 15, 2023 at 12:45 am
Well done! These leds often fail in all sorts of lighting. You'll probably find the ic is a common ic with markings branded specifically for the manufacture of the light. It's not listed on any datasheet site which I've seen. It's sad that often devices have to be scrapped because a component cannot be found.
Kind regards
Albert van Bemmelen
January 18, 2023 at 2:18 pm
Indeed Mohamed. I've seen not listed asics from manufacturers of certain products before too. And that was a 6 pin smd pwm controller in another indoor device too. Like the Melexis mlx02367A chip with smd code '67A'. Luckily the unknown pwm controller was still working fine here! And the smd code used here therefore probably wasn't any valid useful code.