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The AC-DC-AC Inverter Repaired

By on November 23, 2015
ac dc ac inverter repair








This is a local brand  AC- DC- AC INVERTER  that has the ability to convert 12 volt car battery to 220 VAC. It can also charge the car battery with 220 AC.


This machine is good either for charging the battery of car as well as to use it as a source of 220 Ac in places that no electricity is available like sea sides or mountains and out-doors places and etc.

The problem of this inverter was after many years of services, it stopped to work and want to be retired. With no diagram available, I started to repair it after opening the cover:

inverter repair

I found many cold solder joints  and believe this could be the problem. So I resoldered all the dry joints. After done the resoldering work, I started to turn On this device but unfortunately this device refuse to work. I proceeded to check all the transistors and still could not locate any bad transistors on the board either !

Then  next step was to check on all electrolytic  capacitors in the circuit board. I found five bad small caps out of the range with high ESR caps. Some have low capacitance like 10 micro farad 16 volt and 10 micro with 100 volts. The big none polarized cap 0.07 micro 1000 volts that is in series with AC input line checked to be good but ESR value showed open circuit. I replaced this one as well but the device still refuse to work.

This device has a big transformer with 6 big power transistors 2n3055 that converting the 12 volt DC of car battery to 220 AC and one smaller transformer and all were tested good too.

The next test was the relay (HH54S) and when I pumped in the external 12 volt dc to check it, it seems that it was totally dead and no sign of life. I replaced the relay and the device started to work again.




Conclusion: This device had multiple problems:

1-Bad soldering joints

2-Bad caps with high ESR value and

3-A bad relay



This article was prepared for you by Mr Beh from Iran.

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  1. Robert Calk

    November 23, 2015 at 10:22 pm

    Good job, Beh. Thanks for the article.

    • beh

      November 24, 2015 at 12:28 pm

      My friend Robert
      thanks for supports.

  2. Yogesh Panchal

    November 24, 2015 at 12:46 am

    Beh, Good job please keep sharing.

    • beh

      November 24, 2015 at 12:32 pm

      Hi Yogesh
      thanks for your supports . also i always enjoyed of your articles.

  3. Bernie Scott

    November 24, 2015 at 1:16 am

    Good troubleshooting.....Great article......Keep up the good work.....

    • beh

      November 24, 2015 at 12:33 pm

      Hi Bernie
      i am happy you liked the article and thanks

  4. Paris Azis

    November 24, 2015 at 1:27 am

    Hi Beh

    Interesting repair. I always like to work with power supplies and inverters. Many years ago I had one inverter- charger like this one. It looked like this one you repaired and it also used the same power transistors (2N3055).
    Anyway, despite its robust and heavy construction, its output was a non regulated pure rectangular waveform making its practical use very limited as regards sensitive electronic equipment. For ordinary lighting purposes (for resistive loads) it was perfect.
    Apart from that, these “classical” power transistors are really terrible for switching applications due to their very bad (=high) saturation voltage which is well beyond 2,8V at around 8-10A flowing through their C-E terminals, rendering them real “stoves” during their operation and without the use of a “monster” heatsink or an assisting fan they fail very easily because of overheating…
    You brought to me good old memories with your present repair…
    As regards the ESR measurements, please keep in mind that these are meaningless in capacitances below 100nF (or 0,1μF if you prefer). So trying to evaluate that 0,07 bipolar cap (strange capacitance marking anyway!) is beyond the measuring capability of any ESR meter if it operates in 100KHz frequency. It will display an open circuit (meaning above 100Ω of ESR).


    • beh

      November 24, 2015 at 12:46 pm

      Hi Paris
      i always liked your very comprehensive articles specially those about ups s
      about this old invertor i have to say it is about 20-25 years old and as you told does not have very good performances like new ones. same equipment like this recently are made much smaller and lighter and with much better performances . about that none polar cap i have to tell you it was suspected to be culprit and with testing with different ESR meter i gave different result that is why i replaced it . regards beh

  5. Dennis Breda

    November 24, 2015 at 2:00 am

    Thank you for sharing your success on this repair. And thanks to Jestine for providing this platform.

    • beh

      November 28, 2015 at 12:13 pm

      Hi Dennis
      you are most welcome.

  6. Albert van Bemmelen

    November 24, 2015 at 2:15 am

    Good work Beh ! I believe I also saw an older SMPS repair you had fixed in the past. You had worked out that article in great detail. Well done!

    • beh

      November 24, 2015 at 12:49 pm

      Hi Albert
      i always enjoyed of your very scientific articles and i am very happy you liked this one

  7. Joop

    November 24, 2015 at 2:32 am

    Good work!

    • beh

      November 24, 2015 at 12:50 pm

      JOOP thank you

  8. Hermann

    November 24, 2015 at 3:14 am

    Oh, the beloved vintage gear. You never get away with just one fix! In this case, it surprises me how the device worked with all the dead caps until finally the relay broke 😮

    • beh

      November 25, 2015 at 3:06 pm

      Hi HERMAN
      this machine is belong to me and since many years was forgotten but
      due to malfunctioning the battery of my car i decided to bring it back to duty and recharge the battery of my car unfortunately did not helped my car .during those forgotten years of this machine the chines electrolyte of the caps dried out and on that very serious time did not helped me any

  9. Parasuraman S

    November 24, 2015 at 6:54 am

    Good job! I appreciate the 'resurrection' work done by you! In all inverters and UPS, the relay is a common culprit, as it takes the load and over a period of time, the contacts become worn out and/or coil becomes weak. You need to change the parallel diode as well, as a precaution. Best of luck!

    • beh

      November 24, 2015 at 12:55 pm

      i also enjoyed and benefited of your very detailed articles .and thanks for your valuable supports .

  10. Peter O

    November 24, 2015 at 7:33 am

    Good job with sound plan of attack.
    I'd like to hear more about cold soldered joints, how you identify, is there a simple test?
    I once had a CRT TV repaired & the technician said he re-soldered 35 joints "just to be sure"; the main fault lay elsewhere!!

  11. beh

    November 24, 2015 at 1:03 pm

    Hi Peter
    the simple test to verify the cold joints from others is if you bring the tip of your hot solder iron to cold joint on the pcb your solder iron can not melt the cold joint and this need to add some more fresh solder to that point or some solder past to melt the solder actually the equipment older that 5 years show this symptom s in humid part of the world this symptoms are much more makes the problems
    thanks beh

  12. Suranga Electronics

    November 24, 2015 at 3:49 pm

    Good Working...!!!! Thanks.

    • beh

      November 25, 2015 at 3:09 pm

      thanks for supports

  13. mmoni Diphera

    November 24, 2015 at 6:48 pm

    very very interesting plz keep it up

    • beh

      November 25, 2015 at 3:08 pm

      MMONI you are most welcome.

  14. reza

    November 25, 2015 at 3:54 am

    hi beh
    thank u for this good article.

  15. beh

    November 25, 2015 at 3:07 pm

    you are welcome MR REZA.

  16. Bhupendra Thakur

    November 25, 2015 at 10:32 pm

    Dear Beh,Nice work,Keep it up.

  17. beh

    November 28, 2015 at 12:11 pm

    Dear thakur you are welcome

  18. zed

    December 23, 2015 at 4:05 pm

    nice job beh!!!!


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