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Bad Adapter Caused Malfunctioning Of Blue Tooth/USB/FM Player

By on November 3, 2020
blue tooth speaker repair

blue tooth usb fm speaker repair

This is a commonly available USB/FM/Blue Tooth player generally bought for fitting as Car Stereos. These are available as separate module as well as fit in a case like this. The box used is similar to those used for Electronic Choke. I bought this one for my testing as it has Blue Tooth too. Though this was giving some problems, I had no time to look into it and managed. When my son brought his Sony Component System, and wanted to have this module fit in the front case of CD Unit, as he did not want it, I removed this unit and fit it there.

Afterwards I bought a new module and fit it in this case and looked for the causes of power supply related problems. I opened the Adapter, which was luckily fit with four screws. I was surprised to see that a 1000mfd/10V capacitor, though the marking on the Adapter showed 12V. See the pictures below:

power adapter repair

Just two diodes were found used along with this capacitor, on a centre tap transformer, the former of which was rusted already, though I bought this only a few months back. That’s the kind of quality of this cheap Adaptor. Anyhow, my job was to make it work perfectly and I went ahead with my usual rectification job. I replaced the diodes with new ones, connected 103 (0.01uF) fixed capacitor across the diodes, used a 2200/25V cap, used an SMD 5V regulator and soldered the heat zinc portion on the core, after scraping it clean. Added a 220/25V cap to the 5V output. Applied power and found that the 5V was perfect! Checked in Oscilloscope and found that there was no ripple! The DC was perfect!

As the DC jack was found loose, I replaced it with a better one that would fit tightly on the socket. Powered the Unit and found it to be working very well. I isolated the antenna wire and re-routed it through the top, ensuring that the wire does not come anywhere near the power supply or Audio output sockets. This was to ensure that the antenna is isolated and kept as straight as possible to avoid problems in FM reception. Here are a few pictures.

how to repair power adapter from India Technician

how to fix and repair power adaptor

No, no, I would not forget to say ‘Mission accomplished and satisfaction got added to its ……………………….’ (LOL).

This article was prepared for you by Parasuraman Subramanian from India. He is 70 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.

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You may check on his previous repair article below:



  1. Hirari Tech

    November 3, 2020 at 6:20 pm

    thanks too much.very helpfull

    • Parasuraman S

      November 3, 2020 at 9:55 pm

      Many thanks!

  2. Albert van Bemmelen

    November 3, 2020 at 8:15 pm

    Perfect solution like you managed to solder a regulator to the metal core before!
    Of course you only scraped of the rust of the Transformer core where no slats reduce the eddy currents. This way leaving the transformer stacked iron plates packed side with the isolator plates inbetween intact. On the tiny photos it is just hard to see. I believe that on certain AC motors we often do see that on that side the plates are partly welded together. In Audioamplifiers they often reduce the generated transformer field by using a copper encapsulated transformer (Like in expensive Sony audio sets). Or they use the anti-magnetic mu-metal to short the generated field currents to reduce them. Like in oscilloscopes where those fields could influence the direction of the crt emitted electron beam.

    • Parasuraman S

      November 5, 2020 at 12:12 am

      Very keen observation as usual! Many thanks for your detailed analysis and comments!

  3. Lynn Blakely

    November 3, 2020 at 10:50 pm

    Sir Parasuraman: As usual and excellent repair and pictures.

    • Parasuraman S

      November 5, 2020 at 12:13 am

      Many thanks!

  4. Waleed Rishmawi

    November 4, 2020 at 5:22 pm

    it sounded like an intensive surgery was done to this transformer but as always you are in love with such repair job and therefore you are doing your best in everything you do. good job my friend, if it was me, I just buy a 5 volts transformer and get it over with. LOL. have a blessed day and thanks for sharing

    • Parasuraman S

      November 5, 2020 at 12:15 am

      People like me are crazy about servicing and putting back the device to work! And we do a lot of laborious works, without bothering about the time and cost involved! Many thanks for your observation and comments!

  5. Humberto

    November 7, 2020 at 10:46 am

    Good repair, Parasuraman. And of course, satisfaction got added to ……………………. (LOL)

  6. Yogesh Panchal

    November 7, 2020 at 8:13 pm

    Excellent repair! Sir,


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