LED Spotlight Repair (With Video)
When a customer brings in an electronic item for repair, you have to listen carefully to what the symptoms of the fault are as well as any ‘back-story’ that the customer may provide. Sometimes they give you a clue of the origin of the fault and other times they distract you from the correct diagnostic path.
In this case, a customer brought in a big LED spotlight. Some vital information that he included was:
- It didn’t come with a power supply
- He found a power supply with the correct barrel jack plug
- It stopped working soon after he plugged it in
Although I didn’t fully understand how this system worked at the time, I was now armed with the information that the customer had provided. I firstly examined the power supply and checked its operation.
It is a variable power supply, with available voltage of 1.5 – 12 Volts. At this point, I noticed that it was set to 9 Volts – an important point to keep in mind. After testing, no power was present at the output jack.
While disassembling the power supply a fuse was found at the positive input connection. Yes, the fuse was blown and so replacing it would naturally bring back the supply to life – right? No, it did not. Not only that, what caused the fuse to blow? High current must have been present at some point to cause the fuse to blow.
Further testing needed to be done.
My next thought process was to examine the LED light itself. Would it work? Did it have a fault that caused the fuse to blow in the power supply? As I disassembled the spotlight, a vital clue to the failure of the power supply raised its hand.
The LED spotlight contained a rechargeable battery and the required voltage was not 9 Volts as the customer had guessed, but a much lower 3.7 Volts. No wonder the fuse had blown!
After providing 3.7 Volts from a bench variable power supply to the LED input jack, the light came to life!
This proved several things:
- The LED itself was working
- The circuitry within the circuit board was OK
- The switch was operating
So rather than using an appropriate battery charger, the customer had used a voltage supply with a much higher than rated voltage which created the fault in the beginning.
I decided to use a phone battery charger out of my huge collection that I have in my workshop.
After charging the battery all night, the charger indicated a full charge. This was good news.
The next logical step was to find out what damage had been done to the power supply.
This was a learning curve for me at the time. This was a repair that I carried out over 2 years ago and I have learned many things since then. Most importantly, if you have strange readings that indicate a faulty component, take them off-board and retest. At the time, I made several assumptions that led me to incorrect conclusions. As they say, ‘you never stop learning’!
The LED indicator light on the power supply must have had a dry solder joint as after testing it off-board and refitting it, changed it from a non-working component to a working LED.
I removed a suspect transistor from the board and tested it – it also was working correctly.
I tested the electrolytic capacitors using my Blue ESR meter and they also proved to be operational.
I then noticed that the ceramic capacitor at the end of the board was discoloured. Upon further investigation I could see a small split at the top. This was a 2A102K, 1000pF or 1nF capacitor, yet under testing, it was well in the 10nF range. In comparison with the new one, the burnt colour difference was easy to see.
Maybe now I was heading in the right direction!
After replacing the faulty capacitor, another fault raised its hand! Part of the circuit track had been damaged, no doubt due to the higher than acceptable voltage that had been forced into it. This was repaired by bypassing the track with a wire.
At the completion of the repairs, I was able to run the power supply through its full range successfully – 1.5, 3, 4.5, 6, 7.5, 9, 12 Volts. This was tested without load and so the voltages were higher than what the switched voltages were.
That being said, it was handed back to a very happy customer. He now had a LED spotlight that worked, a battery charger rated to the battery requirements and also a repaired power supply that could be used for anything – except the LED Spotlight!
If you are interested in this repair, you can see a video on my channel following the link below.
This article was prepared for you by Mark Rabone from Australia.
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Note: You can check out his previous repair article below:
September 7, 2019 at 12:21 pm
Hi Mark !
Good article and video. Thank's for sharing !
September 7, 2019 at 3:39 pm
September 7, 2019 at 6:46 pm
An article packed with good experience and tips. Many thanks for sharing this. People like you are always an admiration and role model for electronic kids like me! I liked the way, you have presented the case! Deserves special applause!
September 8, 2019 at 4:00 pm
The main thing I learned from this is how little I knew 2 years ago, how much I have learnt in the 2 years since and how much I yet have to learn! 🙂
September 9, 2019 at 12:46 am
Yes, that means we are progressing well!
Robert Calk Jr.
September 8, 2019 at 3:51 am
Good job, Mark!
September 8, 2019 at 4:01 pm
Thanks Robert 🙂
Albert van Bemmelen
September 11, 2019 at 5:31 am
Leaving any comment was before not possible for some strange reason. The Reply function was just missing previously!
Good job Mark. Sadly too many devices get destroyed by using wrong adapters. I even did it myself with an adapter that was unstabilized giving a bit too high 6V output DC voltage to my DY294 Meter/tester. Of course I was able to fix the DY294 and at the same time produced a service manual of the repair afterwards.
September 13, 2019 at 7:14 am
Thanks for your comments. Well done on your meter repair and manual.
Actually I have to raise my hand as well! The very first video I did on my channel, I was testing a microwave oven and didn't realise the very high voltage they produce and you guessed it, my beloved multimeter blew up! A very sad day.... 🙂