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KD -120-12 Power Supply Repaired (Replaced Few Bad Components) 

By on May 17, 2019
power supply repair












I received this power supply for repair.

how to repair power supply

how to fix power supply

The owner of the machine told me this accident has happened:

While he was giving water to plants, water was spilled on this power supply and caused not working any more. This power supply was the source of energy for the LED S that is giving light for growing the plants. I started to repair it.

how to fix and repair power supply

The cover opened by two screws. Inside the machine was a button that by rotating one can set the entrance voltage from 110 to 220v and set voltages.

This is a SMPS power supply and all the major component of such design were present on pcb such as transformers, Schottky diode regulator ic, and so on…  by looking I just found 1 watt resistor with this color coding red, red, gold, gold bands this is a 2.2 ohms  5% and ½ watt .

2.2 ohm resistor burnt

The color bands over this resistor was cracked and showed something happened for it and yes it was opened circuit.  Near to this resistor there were two big transistors that I decided to check them too.

My multi meter proved that these transistors were shorted D13007K. The rest of the semiconductors and other components were found good. I replaced all bad components and started to turn on this machine. Before I restart the machine with the wires of 220 volt I install 100-watt lamp in the place of entrance fuse to test and see if there are more shorted components in the machine or not? The lamp just blinked in a second and then turned off this means no more shorted components in the circuit exist.

power supply series light bulb test

Then I powered up the machine and I received 12 DC volts in output s and the machine returned to service again.

bad components in power supply

Note 1: In this repair I just used the ohm check method and ATLAS DC 75 was proved all the multimeter founding’s and was helpful too. And also Blue Ring tester confirmed that the transformer was good and the repair of the machine was reasonable and economical and the cost was only 50 cents.

NOTE 2:  I also replaced the weak green power indicator LED to a stronger red one.

Note 3: Let me tell you that the 5-amp fuse was intact and showed that this fuse installed just for any entrance AC over amperage and does not care about any shortage inside the circuit actually this machine does not have any protection component against any internal short circuit-bad design.


beh from iran

This article was prepared for you by Mr Beh from Iran

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  1. Albert van Bemmelen

    May 17, 2019 at 7:12 pm

    Very professional repair beh! Like you wrote the 5-amp fuse was still fine and just installed for any entrance AC over-amperage which does not protect against short period shorting currents inside the unit. As you surely know this is the case with many defect SMPS units and they are not only required but also mandatory to prevent against any continuing shorting current that could cause risk of fires if parts get overheated.

    • beh

      May 18, 2019 at 12:03 pm

      yes i also my recommend to use multi fuses or PPTC in such circute for more protection against shorty .And thanks

      • Albert van Bemmelen

        May 19, 2019 at 5:30 pm

        I have installed two 2.5A PPTC's in serie with both Westron Base Speakers in my Elac 50 Watt speaker boxes. This way preventing blowing up and losing my valued Westra kw-160-1324 bass speakers again. I used this PTC calculator:
        And bought two SE250 PPTC's from them for about 20 Euro including shipping. Only shipping made those PPTC's rather expensive but this is always better than replacing the Westra speakers that aren't made anymore sadly. And therefore can't be replaced by equally sounding speakers from other firms because they go higher in frequency and have less Base.

        • beh

          May 21, 2019 at 9:32 pm

          Hi Albert
          Thanks for this very useful link :


  2. Ghashaan

    May 18, 2019 at 12:40 pm

    Great read! It's good that you mentioned about the test equipments that you've used solve this problem. Newbies like I could learn a lot from it.

    • beh

      May 19, 2019 at 1:03 am

      You are welcome
      Yes .also consumed time during repair is important because this effect the cost of repair. And thanks .

  3. Yogesh Panchal

    May 18, 2019 at 9:00 pm

    Well done ! Beh

  4. Raja

    May 18, 2019 at 10:17 pm

    I have etaon 3kva ups in that FET failed, not able find FET part number, any other way to find correct FET.

    • Beh

      May 19, 2019 at 10:13 am

      Ok send s photo from pcb and the fet

  5. beh

    May 19, 2019 at 1:06 am

    Hey Yogesh long time no news from you ?. And you are welcome.

  6. Devon Wilson

    May 20, 2019 at 7:13 am

    Interesting! I didn't know that connecting two fuses in series would cause the amperage to increase. I do know that two resistors connected in series would give a value that is the combined values of the individual resistors.

  7. Justice

    May 20, 2019 at 4:05 pm

    Thank you Beh. You are a star once more. You people do not know how beneficial are your articles not only to me but to the world electronic faternity. keep up the good work.

    • BEH

      May 21, 2019 at 1:39 pm

      Thanks Justice for your warm words. And you are welcome.

  8. Parasuraman Subramanian

    May 20, 2019 at 4:57 pm

    Well done! A professional approach with systematic presentation making the article highly attractive to read!

  9. beh

    May 21, 2019 at 1:41 pm



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