What An Ingenius Way To Solve A Power Supply With Burnt Components
This Urban Disco active speaker came in with the complaint of no power. The first thing to do is to open up the cover and check if the main fuse is ok or not. There are five circuit boards in this set and my concentration was in the power supply board.
The power supply output power is 16 volt with 3 ampere-see the photos below:
The main fuse was heavily burnt due to that you can see the fuse glass is in dark color-see the photo below:
There must be components that had caused the main fuse to burnt badly. So I removed the power supply to check on the suspected component such as the bridge rectifier. Before I could check on the bridge rectifier, I found the power supply primary side had few burnt to crisp SMD components-see the photos below:
In order to know if only the power supply fault or if other boards have problem, I have connected an external 16 volt power supply to test out the whole unit.
After connected with the external power supply, the active speaker came back to life. This also means only the power supply have problem.
Since I can’t find the service manual or the schematic diagram of this power supply, I won’t be able to know the exact value of the burnt components. This situation made me had to come out with a solution which is to make my own power supply to power up the set. I bought a linear transformer, two diodes (1n5408), a filter cap (2200uf 50 volt) and a main fuse to fix it to become a power supply unit to replace the original power supply. You can Google for center tapped fullwave linear power supply schematic.
Once done fixing the new power supply and Powered On, the set came back to life again. I purposely turned the volume to max and see if there is any drop in the sound and it was perfectly fine.
I even tested this active speaker with my phone to blue-tooth and all worked superb.
Conclusion- Sometimes in electronics repair we just could not repair a broken item/section due to the unavailability of parts or service info. The best is to use the modification method. If you are thinking to learn modification method in small switch mode power supplies you can check out Jestine’s Ebook HERE.
This article was prepared for you by Suranga Bandara who owns an Electronics repair shop in Anuradapura, Sri Lanka.
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Note: You may check out his previous post in the below links:
https://jestineyong.com/guess-which-component-that-had-caused-vibration-sound-in-telesonic-speaker/
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Parasuraman
July 16, 2018 at 9:30 pm
Excellent novel solution!
Albert van Bemmelen
July 17, 2018 at 4:36 am
Removing the old bad 16V 3A smps power supply and replacing it by a linear power supply seems to be the best option. Since cheap 16V 3A smps adapters are hard to find. Hopefully the load is safely capable to limit the open voltage to max 16V at 3A all the time.
Suranga Electronics
July 18, 2018 at 1:49 pm
yes Mr, Albert.
Thank You!
James
July 17, 2018 at 2:44 pm
"Improvise" good job'
Justice
July 17, 2018 at 9:27 pm
Thanks Suranga, interesting information.
Parasuraman S
July 21, 2018 at 12:54 pm
You can use a Universal Module, which I have described in my many articles on repair of CRT TV and others, and just connect it in place of the PWM, and then adjust the voltage to the required level. By this way, we ensure that the original secondary is sustained, which is more important.